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An ideal resource for the classroom or clinical setting, Sectional Anatomy for Imaging Professionals, 4th Edition provides a comprehensive, and highly visual approach to the sectional anatomy of the entire body. Side-by-side presentations of actual diagnostic images from both MRI and CT modalities and corresponding anatomic line drawings illustrate the planes of anatomy most commonly demonstrated by diagnostic imaging. Easy-to-follow descriptions detail the location and function of the anatomy, while clearly labeled images help you confidently identify anatomic structures during clinical examinations. In all, it’s the one reference you need to consistently produce the best possible diagnostic images.

Key Features

  • • Side-by-side presentation of anatomy illustrations and corresponding CT and MRI images clarifies the location and structure of sectional anatomy.
  • • More than 1,500 high-quality images and detailed line drawings demonstrate sectional anatomy for every body plane commonly imaged in the clinical setting.
  • • Updated summary tables are used to simplify and organize key information in each chapter.
  • • CT or MR images of special interest are featured on the opening page in each chapter to pique readers’ interest in the area about to be covered in the text.
  • • Reference drawings and corresponding scanning planes appear on appropriate pages with the actual images, so they are easily referenced for correlation between the scanning planes and the resulting images.
  • • Introductory chapter lays a foundation of the terminology that is related to sectional anatomy.
Year:
2018
Edition:
4th
Publisher:
Elsevier
Language:
english
Pages:
792 / 794
ISBN 13:
9780323414876
File:
PDF, 724.59 MB
Download (pdf, 724.59 MB)

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SECTIONAL
ANATOMY
For Imaging
Professionals
FOURTH
EDITION
LORRIE L. KELLEY, MS, RT(R)(MR)(CT)
Associate Professor Emeritus
Boise State University
Boise, Idaho

CONNIE M. PETERSEN, MS, RT(R)(CT), MS, LPC
Former Adjunct Instructor, Radiologic Sciences Program
Boise State University
Boise, Idaho

3251 Riverport Lane
St. Louis, Missouri 63043

SECTIONAL ANATOMY FOR IMAGING PROFESSIONALS, FOURTH EDITION

ISBN: 978-0-323-41487-6

Copyright © 2018, Elsevier Inc. All Rights Reserved.
Previous editions copyrighted 2013, 2007, 1997
No part of this publication may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission and further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center
and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.
This book and the individual contributions contained in it are protected under copyright by the Publisher (other
than as may be noted herein).

Notices
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and
using any information, methods, compounds or experiments described herein. Because of rapid advances
in the medical sciences, in particular, independent verification of diagnose; s and drug dosages should be
made. To the fullest extent of the law, no responsibility is assumed by Elsevier, authors, editors or contributors for any injury and/or damage to persons or property as a matter of products liability, negligence
or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in
the material herein.
Library of Congress Cataloging-in-Publication Data
Names: Kelley, Lorrie L., author. | Petersen, Connie M., author.
Title: Sectional anatomy for imaging professionals / Lorrie L. Kelley, Connie
M. Petersen.
Description: Fourth edition. | St. Louis, Missouri : Elsevier, [2018] |
Identifiers: LCCN 2017056253 (print) | LCCN 2017056842 (ebook) | ISBN
9780323595377 (Ebook) | ISBN 9780323414876 (pbk. : alk. paper)
Subjects: | MESH: Anatomy | Magnetic Resonance Imaging | Tomography | Atlases
Classification: LCC QM25 (ebook) | LCC QM25 (print) | NLM QS 17 | DDC
612.0022/3—dc23
LC record available at https://lccn.loc.gov/2017056253

Executive Content Strategist: Sonya Seigafuse
Content Development Manager: Lisa Newton
Senior Content Development Specialist: Danielle M. Frazier
Publishing Services Manager: Deepthi Unni
Senior Project Manager: Manchu Mohan
Design Direction: Brian Salisbury

Printed in the United States of America
Last digit is the print number: 9 8

7

6

5

4

3

2

1

Til James,
Min beste venn og evig ledsager. Jeg smil hver dag på grunn av deg.
Your strength sustains me, your
love elevates me, and your faith inspires me.
To my greatest treasures:
Kristina, Matt, Jennifer, John, Michael, Natalie, Angela, Blair and Jamers, Daniel,
Dean, Maren, Evelyn, McKenzie, Jakob, Anders, Alyssa, Margalit, and Porter
Your laughter brings me joy, your enthusiasm for learning is contagious,
and your support and love for each other is the grandest example of selfless service.
Thanks for reminding me to dream.
To my parents, Bill and Darhl Buchanan,
for sharing your wisdom and encouragement
in ways that strengthen and inspire me.
To Connie,
for your perseverance in collaborating with me
through four editions while keeping your sense of humor.
And to the many medical professionals who elevate their professions by serving with
humility, compassion, and a reverence for life.
LLK

Thank you to my family and friends whose guidance, love, and support carried me through
my most trying times.
I dedicate this book to:
My family, Mom, Dad, Brayden, Trinity, Grant, Scott, Kendra, Colton, and Jayden,
who are my greatest blessings and who deeply enrich my life with laughter, joy, support,
and true love. When I need you most, you never fail to show up with a hug, smile, or words of
encouragement. Thank you for your understanding as I focused much of my time working
on this fourth edition.
You are my heart and soul and I love you dearly.
To Lorrie,
my friend and colleague for whom I have the utmost admiration. What a true pleasure it has been
to work with you all these years. You truly kept me motivated and even when I was most frustrated,
you somehow made me laugh. You are amazing.
To my colleagues for their gifts of support and wisdom. And to my clients and a group
of extraordinary young women who amaze me with their bravery and strength as they strive
for greater wellness in their lives. You are truly special.
And to the medical professionals who utilize this book in their pursuit of knowledge to improve patient
care and advance the field of radiologic sciences.
CMP

Reviewers
Lisa Fanning, MEd, RT(R)(CT)
Chair
School of Medical Imaging
& Therapeutics
Massachusetts College of Pharmacy
and Health
Sciences University
Boston, MA
Rebecca Farmer, MSRS, RT(R)(M)
Associate Professor of Allied Health
and Radiologic Science
School of Allied Health
Northwestern State University
Shreveport, LA

iv

Kathy Kienstra, MAT, RT(R)(T)
Associate Professor
Program Director, Radiation Therapy
Program
Doisy College of Health Sciences
Saint Louis University
St. Louis, MO

Kenneth A. Roszel, MS, RT(R)
Program Director
Radiology
Geisinger Medical Center
Danville, PA

Preface
This text was written to address the needs of today’s
practicing health professional. As technology in diagnostic imaging advances, so does the need to competently
recognize and identify cross-sectional anatomy. Our goal
was to create a clear, concise text that would demonstrate in an easy-to-use yet comprehensive format the
anatomy the health professional is required to understand to optimize patient care. The text was purposely
designed to be used both as a clinical reference manual
and as an instructional text, either in a formal classroom
environment or as a self-instructional volume.
Included are close to 1000 high-quality MR and CT
images for every feasible plane of anatomy most commonly imaged. An additional 350 anatomic maps and
line drawings related to the MR and CT images add to
the learner’s understanding of the anatomy being studied. In addition, pathology boxes describe common pathologies related to the anatomy presented, assisting the
reader in making connections between the images in the
text and common pathologies that will be encountered
in clinical practice. Updated tables are used to summarize and organize key information in each chapter. For
example, tables that summarize muscle group information include points of origin and insertion, as well as
functions, for the muscle structures pertinent to the images the reader is studying.

NEW TO THIS EDITION
• Updated content to reflect the latest ARRT and ASRT
curriculum guidelines
• Expanded images in the lymphatic system
• Second color added to the design to make difficult
content easier to digest

identifying the desired anatomy during actual clinical
examinations. The narrative accompanying these images
clearly and concisely describes the location and function
of the anatomy in a format easily understood by health
professionals. The text is divided into chapters by
anatomic regions. Each chapter of the text contains an
outline that provides an overview of the chapter’s contents, pathology boxes that briefly describe common
pathologies related to the anatomy being presented,
tables designed to organize and summarize the anatomy
contained in the chapter, and reference illustrations that
provide the correct orientation for ease of locating the
anatomy of interest.

ANCILLARIES
A Workbook and an Evolve site complement the text.
When used together, these additional tools create a
virtual learning system/reference resource.
Workbook: The Workbook provides practice opportunities for the user to identify specific anatomy. The
Workbook includes learning objectives that focus on the
key elements of each chapter, a variety of practice items
to test the reader’s knowledge of key concepts, labeling
exercises to test the reader’s knowledge of the anatomy,
case studies to provide relevance for clinical applications, and answers to exercises.
Student Resources on Evolve: An image collection
with approximately 1000 images.
Instructor Resources on Evolve: These resources include
a test bank with approximately 500 questions and an
image collection with approximately 1000 images.
Lorrie L. Kelley
Connie M. Petersen

CONTENT AND ORGANIZATION
The images include identification of vital anatomic structures to assist the health professional in locating and

v

This page intentionally left blank

Acknowledgments
Many provided encouragement and direction as the
compilation of this text commenced. Danielle Frazier
and Manchu Mohan had the tiresome duty of encouraging us to meet deadlines, which they did with grace and
patience. Sonya Seigafuse had the daunting task of strategically pulling it all together. We are indebted to them
for their editorial assistance in seeing this project through
completion. We wish to extend our gratitude to everyone
who thought the first, second, and third editions had
value and to those who took the time to provide constructive criticism and suggestions for further improvements and increased accuracy. And to the many students,
peers, and colleagues for providing feedback so that we
could see the text from many different perspectives.
The following individuals and institutions deserve
special acknowledgment:
• Chris Hayden for his tremendous patience, knowledge, and time invested in helping us find and create

all of the new CT images for the third edition. And
St. Alphonsus Regional Medical Center for providing
the CT images.
• Mary Pullin from Philips Medical Systems for providing
some beautiful MR images.
• Dave Arnold and St. Luke’s Regional Medical Center,
as well as Kevin Bean and Intermountain Medical
Imaging, for providing the majority of the MR
images.
We owe a debt of gratitude to Marie Dean who provided numerous new illustrations and revised many old
drawings creating more accuracy and consistency in the
visual presentation of the artwork throughout the text.
Lorrie L. Kelley
Connie M. Petersen

vii

This page intentionally left blank

Table of Contents
1

Introduction to Sectional
Anatomy, 1

2

Cranium and Facial Bones, 13

3

Brain, 86

4

Spine, 172

5

Neck, 250

	  6

Thorax, 309

	  7

Abdomen, 399

	  8

Pelvis, 497

	  9

Upper Extremity, 568

10

Lower Extremity, 659

ix

This page intentionally left blank

CHAPTER

1

Introduction to Sectional
Anatomy
Iliopsoas
muscle Sartorius
muscle Femoral
Acetabulum
head

Tensor fasciae
latae muscle
Gluteus medius
muscle

R
Coccygeus muscle

L
Rectum

Coccyx

Gluteus maximus
muscle

FIG. 1.1 Axial CT of hips.

Sectional anatomy has had a long history. Beginning as
early as the 16th century, the great anatomist and artist
Leonardo da Vinci was among the first to represent the
body in anatomic sections. In the following centuries,
numerous anatomists continued to provide illustrations of
various body structures in sectional planes to gain greater
understanding of the topographical relationships of the
organs. The ability to see inside the body for medical purposes has been around since 1895, when Wilhelm Conrad
Roentgen discovered x-rays. Since that time, medical imaging has evolved from the two-dimensional (2D) image
of the first x-ray to the 2D cross-sectional images of computed tomography (CT) and magnetic resonance imaging
(MRI), then to the three-dimensional (3D) imaging techniques used today. These changes warrant the need for
medical professionals to understand and identify human
anatomy in both 2D and 3D images.
Sectional anatomy emphasizes the physical relationship
between internal structures. Prior knowledge of anatomy
from drawings or radiographs may assist in understanding
the location of specific structures on a sectional image. For
example, it may be difficult to recognize all the internal
anatomy of the pelvis in cross-section, but by identifying
the femoral head on the image, it will be easier to recognize soft tissue structures adjacent to the hip (Fig. 1.1).

OBJECTIVES
• Define the four anatomic planes.
• Describe the relative position of specific structures
within the body using directional and regional
terminology.
• Identify commonly used external landmarks.
• Identify the location of commonly used internal
landmarks.

• Describe the dorsal and ventral cavities of the body.
• List the structures located within the four abdominal
quadrants.
• List the nine regions of the abdomen.
• Describe the gray scale used in CT and MR imaging.
• Describe MPR, CPR, SSD, MIP, and VR.
• Differentiate between 2D and 3D images.

OUTLINE
ANATOMIC POSITIONS
AND PLANES, 2
TERMINOLOGY AND
LANDMARKS, 2
External Landmarks, 4
Internal Landmarks, 4
BODY CAVITIES, 4

ABDOMINAL AND PELVIC
DIVISIONS, 4
Quadrants, 6
Regions, 6
IMAGE ACQUISITION, 7
IMAGE DISPLAY, 7

Copyright © 2019, Elsevier Inc.

MULTIPLANAR REFORMATION
AND 3D IMAGING, 8
Multiplanar Reformation
(Reformat) (MPR), 8
Curved Planar Reformation
(Reformat) (CPR), 8
3D Imaging, 8
1

CHAPTER 1 Introduction to Sectional Anatomy

2

S

ANATOMIC POSITIONS AND PLANES
For our purposes, sectional anatomy encompasses all the
variations of viewing anatomy taken from an arbitrary
angle through the body while in anatomic position.
In anatomic position, the body is standing erect, with
the face and toes pointing forward and the arms at the side,
with the palms facing forward. Sectional images are commonly acquired and displayed according to one of the four
fundamental anatomic planes that pass through the body
(Fig. 1.2). The four anatomic planes are defined as follows:
1. Sagittal plane: a vertical plane that passes through the
body, dividing it into right and left portions
2. Coronal plane: a vertical plane that passes through
the body, dividing it into anterior (ventral) and posterior (dorsal) portions
3. Axial (transverse) plane: a horizontal plane that
passes through the body, dividing it into superior and
inferior portions
4. Oblique plane: a plane that passes diagonally between
the axes of two other planes
Medical images of sectional anatomy are, by convention, displayed in a specific orientation. Images are
viewed with the right side of the image corresponding to
the viewer’s left side (Fig. 1.3).

Median sagittal plane

P

Median coronal plane

A

I
Sagittal
A

ial
Ax ne
l
pa

R

L

P

Oblique
plane

Axial (transverse)
S

r
rio
te al)
s
o rs
r P do
R
io l) (
r
te ra
An ent
(v

L

I
Coronal

TERMINOLOGY AND LANDMARKS

FIG. 1.2 Anatomic position and planes of the body.

Directional and regional terminology is used to help describe the relative positions of specific structures within
the body. Directional terms are defined in Table 1.1, and
regional terms are defined in Table 1.2 and demonstrated in Fig. 1.4.

Sacrum S
Liver

Lumbar
vertebra

Ilium

Stomach

A

R

L

L

R

Inferior
vena cava

B
A
P

Aorta

Spleen

A = anterior L = left
P = posterior S = superior
R = right
I = inferior

FIG. 1.3 (A) Axial CT of abdomen. (B) 3D CT of pelvis (anterior view).

I

Femur

CHAPTER 1 Introduction to Sectional Anatomy
TABLE 1.1

Directional Terminology

Direction

Definition

Superior
Inferior
Anterior/ventral
Posterior/dorsal
Medial
Lateral
Proximal
Distal
Superficial
Deep
Cranial/cephalic
Caudal
Rostral
Ipsilateral
Contralateral
Thenar
Volar

Above; at a higher level
Below; at a lower level
Toward the front or anterior surface of the body
Toward the back or posterior surface of the body
Toward the midsagittal plane
Away from the midsagittal plane
Toward a reference point or source within the body
Away from a reference point or source within the body
Near the body surface
Farther into the body and away from the body surface
Toward the head
Toward the feet
Toward the nose
On the same side
On the opposite side
The fleshy part of the hand at the base of the thumb
Pertaining to the palm of the hand or flexor surface of the wrist or the sole
of the foot
The front or palm of the hand
The sole of the foot

Palmar
Plantar

TABLE 1.2

Regional Terminology

Direction
Abdominal
Antebrachial
Antecubital
Axillary
Brachial
Buccal
Carpal
Cephalic
Cervical
Costal
Crural
Cubital
Cutaneous
Femoral
Flank
Frontal
Gluteal
Inguinal
Lumbar
Occipital
Ophthalmic
Otic
Pectoral/mammary
Pedal
Pelvic
Perineal
Plantar
Popliteal
Sacral
Sternal
Sural
Tarsal
Thoracic
Umbilical
Vertebral

Definition
Abdomen
Forearm
Front of elbow
Armpit
Upper arm
Cheek
Wrist
Head
Neck
Ribs
Leg
Posterior surface of elbow area of the arm
Skin
Thigh, upper portion of leg
Side of trunk adjoining the lumbar region
Forehead
Buttock
Groin
Lower back between the ribs and hips
Back of the head
Eye
Ear
Upper chest or breast
Foot
Pelvis
Perineum
Sole of foot
Back of knee
Sacrum
Sternum
Calf
Ankle
Chest
Navel
Spine

3

4

CHAPTER 1 Introduction to Sectional Anatomy

Cephalic

Ophthalmic
Buccal

Frontal
Otic
Oral

Occipital
Cervical

Sternal
Brachial
Antecubital
Antebrachial
(cubital)

Pectoral/
mammary

Axillary
Thoracic

Vertebral
Cubital

Costal
Abdominal

Carpal

Lumbar

Flank

Sacral

Pelvic

Palmar

Gluteal
(buttock)

Umbilical
(navel)

Inguinal
(groin)

Perineal
Femoral
(thigh)
Crural

Tarsal

Popliteal

Sural

Cutaneous
(skin)

Plantar

Pedal

FIG. 1.4 Regional terminology of the body.

External auditory meatus (EAM)

External Landmarks
External landmarks of the body are helpful in identifying
the location of many internal structures. The commonly
used external landmarks are shown in Figs. 1.5 and 1.6.

Internal Landmarks
Internal structures, in particular, vascular structures,
can be located by referencing them to other identifiable
regions or locations, such as organs or the skeleton
(Table 1.3).

Nasion
Mastoid
tip

C1

Acanthion
Gonion

BODY CAVITIES
The body consists of two main cavities: the dorsal and
ventral cavities. The dorsal cavity is located posteriorly
and includes the cranial and spinal cavities. The ventral
cavity, the largest body cavity, is subdivided into the thoracic and abdominopelvic cavities. The thoracic
cavity is further subdivided into two lateral pleural
cavities and a single, centrally located cavity called the
mediastinum. The abdominopelvic cavity can be subdivided into the abdominal and pelvic cavities (Fig. 1.7). The
structures located in each cavity are listed in Table 1.4.

ABDOMINAL AND PELVIC DIVISIONS
The abdomen is bordered superiorly by the diaphragm
and inferiorly by the pelvic inlet. The abdomen can be

C3
C5

Thyroid
cartilage

C7

Vertebral
prominens

Jugular
notch

FIG. 1.5 External landmarks of the head and neck.

divided into four quadrants or nine regions. These divisions are useful in identifying the general location of
internal organs and provide descriptive terms for the
location of pain or injury in a patient’s history.

CHAPTER 1 Introduction to Sectional Anatomy
TABLE 1.3
C5 and thyroid cartilage
T1
T2, T3, and jugular notch
T4, T5, and sternal angle

T10 and xiphoid process

Internal Landmarks

Landmark

Location

Aortic arch
Aortic bifurcation
Carina
Carotid bifurcation
Celiac trunk
Circle of Willis
Common iliac vein
bifurcation
Conus medullaris
Heart—apex

2.5 cm below jugular notch
L4–L5
T4–T5, sternal angle
Upper border of thyroid cartilage
4 cm above transpyloric plane
Suprasellar cistern
Upper margin of sacroiliac joint

L3 and costal margin

Heart—base

L3, L4, and level of umbilicus
L4 and crest of ilium

Inferior mesenteric artery

S1 and anterior
superior iliac spine

Inferior vena cava
Portal vein
Renal arteries

Coccyx, symphysis pubis,
and greater trochanters

5

Superior mesenteric artery
Thyroid gland
Vocal cords

FIG. 1.6 External landmarks of the body.

T12–L1, L2
5th intercostal space, left
midclavicular line
Level of 2nd and 3rd costal
cartilages behind sternum
4 cm above bifurcation of
abdominal aorta
L5
Posterior to pancreatic neck
Anterior to L1, inferior to superior
mesenteric artery
2 cm above transpyloric plane
Thyroid cartilage
Midway between superior and
inferior border of thyroid
cartilage

Brain in
cranial cavity
Spinal cord
in vertebral canal
(spinal cavity)

Trachea

Mediastinum

Lung

Thoracic
cavity

Thoracic
cavity

Heart

Pleural
cavity

Dorsal
cavities

Abdominal
cavity

Diaphragm
Ventral
cavities

Diaphragm

Spleen

Liver

Abdominal
cavity

Stomach

Pancreas

Transverse
colon

Small
intestine

Descending
colon

Ascending
colon
Pelvic
cavity

A

B

Appendix

Pelvic
cavity

FIG. 1.7 (A) Lateral view of body cavities. (B) Anterior view of body cavities.

Abdominopelvic
cavity

CHAPTER 1 Introduction to Sectional Anatomy

6

TABLE 1.4

Main Body Cavities
Dorsal
Cranial
Spinal
Ventral
Thoracic
• Mediastinum
• Pleural
Abdominopelvic
• Abdominal

• Pelvic

For a description of the structures located within each
quadrant, see Table 1.5.

Body Cavities
Contents

Regions

• Brain
• Spinal cord and vertebra

The abdomen can be further divided by four planes into
nine regions. The two transverse planes are the transpyloric and transtubercular planes. The transpyloric plane is
found midway between the xiphisternal joint and the umbilicus, passing through the inferior border of the L1
vertebra. The transtubercular plane passes through the
tubercles on the iliac crests, at the level of the L5 vertebral
body. The two sagittal planes are the midclavicular lines.
Each line runs inferiorly from the midpoint of the clavicle
to the midinguinal point (Fig. 1.8B). The nine regions can
be organized into three groups:

• Thymus, heart, great vessels,
trachea, esophagus, and
pericardium
• Lungs, pleural membranes
• Peritoneum, liver, gallbladder,
pancreas, spleen, stomach,
intestines, kidneys, ureters, and
blood vessels
• Rectum, urinary bladder, male
and female reproductive system

Quadrants
The midsagittal and transverse planes intersect at the
umbilicus to divide the abdomen into four quadrants
(Fig. 1.8A):
Right upper quadrant (RUQ)
Right lower quadrant (RLQ)
Left upper quadrant (LUQ)
Left lower quadrant (LLQ)

Superior
• Right hypochondrium
• Epigastrium
• Left hypochondrium
Middle
• Right lateral
• Umbilical
• Left lateral
Inferior
• Right inguinal
• Hypogastrium
• Left inguinal

Right
midclavicular
plane

Midsagittal
plane

Left
midclavicular
plane

Epigastrium
Right
hypochondrium

Left
hypochondrium
Transpyloric plane

RUQ

LUQ

Right lateral

Transverse
plane

Hypogastrium
RLQ

A

Umbilical

LLQ

Right inguinal

B
FIG. 1.8 (A) Four abdominal quadrants. (B) Nine abdominal regions.

Left lateral
Transtubercular
plane
Left inguinal

CHAPTER 1 Introduction to Sectional Anatomy
TABLE 1.5

7

Organs Found Within Abdominopelvic Quadrants

Quadrant

Organs

Right upper quadrant (RUQ)
Left upper quadrant (LUQ)
Right lower quadrant (RLQ)
Left lower quadrant (LLQ)

Right lobe of liver, gallbladder, right kidney, portions of stomach, small and large intestines
Left lobe of liver, stomach, tail of the pancreas, left kidney, spleen, portions of large intestines
Cecum, appendix, portions of small intestine, right ureter, right ovary, right spermatic cord
Most of small intestine, portions of large intestine, left ureter, left ovary, left spermatic cord

IMAGE ACQUISITION
The images displayed in this text are acquired from MRI
and CT scanners. MRI uses a strong magnetic field
in conjunction with nonionizing radiofrequency (RF)
energy to acquire images. CT uses ionizing radiation to
acquire images. Both modalities are capable of creating
2D and 3D images.

IMAGE DISPLAY
Each digital image can be divided into individual regions called pixels or voxels that are then assigned a
numerical value corresponding to a specific tissue property of the structure being imaged (Fig. 1.9). The
numerical value of each voxel is assigned a shade of
gray for image display. In CT, the numerical value (CT
number) is referenced to a Hounsfield unit (HU), which
represents the attenuating properties or density of each
tissue. Water is used as the reference tissue and is given

a value of zero. A CT number greater than zero will
represent tissue that is denser than water and will
appear in progressively lighter shades of gray to white.
Tissues with a negative CT number will appear in progressively darker shades of gray to black (Fig. 1.10). In
magnetic resonance (MR), the gray scale represents the
specific tissue relaxation properties of T1, T2, and proton density. The gray scale in MR images can vary
greatly because of inherent tissue properties and can
appear different with each patient and across a series of
images (Fig. 1.11).
The appearance of digital images can be altered to
include more or fewer shades of gray by adjusting the
gray scale, a process called windowing. Windowing is
used to optimize visualization of specific tissues or lesions. Window width (WW) is a parameter that allows
for the adjustment of the gray scale (number of shades of
gray), and window level (WL) basically sets the density
of the image or the center of the gray scale (Fig. 1.10).

Pixel
Voxel

FIG. 1.9 Representation of a pixel and voxel.

8

CHAPTER 1 Introduction to Sectional Anatomy

Gray scale
display

CT number (HU)
White

256
gray
shades

Black

1000
900
800
700
600
500
400
300
200
100
0
–100
–200
–300
–400
–500
–600
–700
–800
–900
–1000

Bone
window

WW 2000
WL 250

Dense
bone

Bone

Mediastinal
Muscle
Soft
window
Water = 0
tissue

WW 350
WL 50

Fat

Lung
tissue

Air

Lung
window

WW 1500
WL 500

FIG. 1.10 CT numbers and windowing on axial CT of chest.

MULTIPLANAR REFORMATION AND
3D IMAGING

Curved Planar Reformation
(Reformat) (CPR)

Several postprocessing techniques can be applied to the
original 2D digital data to provide additional 3D information. All current postprocessing techniques depend
on creating a digital data stack from the original 2D
images, thereby generating a cube of digital information
(Fig. 1.12).

Images are reconstructed from data obtained along
an arbitrary curved projection through the cube
(Fig. 1.15).

Multiplanar Reformation
(Reformat) (MPR)
Images reconstructed from data obtained along any projection through the cube result in a sagittal, coronal,
axial, or oblique image (see Figs. 1.13 and 1.14).

3D Imaging
All 3D algorithms use the principle of ray tracing in
which imaginary rays are sent out from a camera viewpoint. The data are then rotated on an arbitrary axis,
and the imaginary ray is passed through the data in
specific increments. Depending on the method of reconstruction, unique information is projected onto the
viewing plane (Fig. 1.16).

Transverse magnetization

T1 (63% recovery
to equilibrium)
90°

A

B

Lo
ng
T

t
or
Sh

Longitudinal magnetization

CHAPTER 1 Introduction to Sectional Anatomy

T2

(e
.g

2 (e

., s
o

.g.,

C

wat

9

D

er )

lid t
issue
)

TE
Time
T1 for solid tissue
T1 for free water
T1 Relaxation

T2 Relaxation

T1-weighted

T2-weighted

Proton density–weighted

FIG. 1.11 MR tissue relaxation and image contrast.

2

4
1

7

5

7

2
7

7

8

7

8

8

6

7

7

9

4

7

7

7

2

3

1
9

4

7

3

8
7
9
7
4

Sagittal
plane

3

Oblique
plane

7
9

8

1

5

A

6

2
7
6

7

4
5

2

5
Coronal
plane

B

Axial
plane

FIG. 1.12 (A) Digital cube. (B) Stack of axial image data.

CHAPTER 1 Introduction to Sectional Anatomy

10

Overview

Shaded surface
display

Axial

Volume rendering

Sagittal

Coronal

MIP

FIG. 1.13 Multiplanar reformation and 3D.
P

P
2

4
1
1
6
4
5

6
7

5

7

2
7

7

8

7

8

7

7

7

7

2

3

R

8
8
9
7
4

1
9

7

7
9

4

1

7

1

4

6

5
2

4

5

5

6

2

4
2

6
7

3

7

9

8

7

3

7

5

7
7

7

7

7

2

7

7

8
8

7

2

3

P
1
9

8
8
9
7
4

7

7
9

4

4

Sagittal

6

5
2

4

5

R
A

1

A

Axial (transverse)

FIG. 1.14 Multiplanar reformations of brain.

R

5

7

5

7

1

7

6

2

4
2

6
7

3

7

9

8

7

3

7

2

8
8

7

7

7

7

2

7

7

3
A

Coronal

8
8
9
7
4

1
9

7

7
9

4

2
7
6

7
5

3

7

9

8

7

3

4
5

2

CHAPTER 1 Introduction to Sectional Anatomy

11

Voxels
2

4
1
1
6

6
7

5

7
7
7

2
7

7

8
8
7

8
8
9

4

7

7

7

5

2

3

4

1
9

7

7
9

4

2
7
6

7

3

7

9

8

7

3

4

MPR

5
2

5

CPR

FIG. 1.15 Image reformation. MPR, Multiplanar reformation; CPR,
curved planar reformation.

Shaded Surface Display (SSD). A ray from the

camera’s viewpoint is directed to stop at a particular
user-defined threshold value. With this method, every
voxel with a value greater than the selected threshold is
rendered opaque, creating a surface. That value is then
projected onto the viewing screen (Fig. 1.17).

Maximum Intensity Projection (MIP). A ray from

the camera’s viewpoint is directed to stop at the voxel
with the maximum signal intensity. With this method,
only the brightest voxels will be mapped into the final
image (Fig. 1.18).

Pix
els
alo
ng
ray
Displayed pixel

FIG. 1.16 Ray tracing.

Volume Rendering (VR). The contributions of each

voxel are summed along the course of the ray from the
camera’s viewpoint. The process is repeated numerous
times to determine each pixel value that will be displayed
in the final image (Fig. 1.19).

S

Pix
els
alo
ng
ray

Displayed pixel
I

FIG. 1.17 Shaded surface display (SSD).

12

CHAPTER 1 Introduction to Sectional Anatomy
S

Projected
value
Maximum
intensity

Pix
els
alo
ng
ray

I

FIG. 1.18 Maximum intensity projection (MIP).
S

Pix
els
alo
ng
ray
Displayed pixel
I

FIG. 1.19 Volume rendering (VR).

REFERENCES
Curry, R. A., & Tempkin, B. B. (2010). Sonography: Introduction
to normal structure and functional anatomy (3rd ed.).
St. Louis: Saunders.
Frank, E., & Long, B. (2011). Merrill’s atlas of positioning and
radiographic procedures (12th ed.). St. Louis: Mosby.

Seeram, E. (2008). Computed tomography; physical principles,
clinical applications, and quality control (3rd ed.). Philadelphia:
Saunders.

CHAPTER

2

Cranium and Facial Bones
Gentlemen, damn the sphenoid bone!
Oliver Wendell Holmes (1809–1894),
Opening of anatomy lectures at Harvard Medical School

The complex anatomy of the cranium and facial bones
can be intimidating. However, with three-dimensional
(3D) imaging and multiple imaging planes, the task of
identifying these structures can be simplified. It is important to understand the normal sectional anatomy of the
cranium and facial bones to identify pathologic disorders and injuries that may occur within this area
(Fig. 2.1). This chapter demonstrates the sectional anatomy of the structures listed in the outline.

FIG. 2.1 3D CT of skull. Trauma resulting from a gunshot wound.

OBJECTIVES
• Differentiate between the three cranial fossae.
• Identify the location and unique structures of each
cranial and facial bone.
• Identify the structures of the external, middle, and
inner ear, and describe their functions.
• Identify the cranial sutures.
• Describe the six fontanels in the infant cranium.
• Describe the structures that constitute the
temporomandibular joint.

• Identify the location of each paranasal sinus and the
meatus into which it drains.
• Identify the structures of the osteomeatal unit.
• Identify the bones that form the orbit and their
associated openings.
• Describe the structures that constitute the globe of
the eye.
• List the muscles of the eye, and describe their
functions and locations.

OUTLINE
CRANIUM, 14
Parietal Bone, 18
Frontal Bone, 18
Ethmoid Bone, 21
Sphenoid Bone, 23
Occipital Bone, 27
Temporal Bone, 30
Structures of the External,
Middle, and Inner Ear, 35
Sutures, 44
Fontanels, 47
FACIAL BONES, 49
Nasal Bones, 50

Lacrimal Bones, 50
Palatine Bones, 50
Maxillary Bones, 50
Zygomatic Bones, 53
Inferior Nasal Conchae, 56
Vomer, 56
Mandible, 57
TEMPOROMANDIBULAR
JOINT, 60
Bony Anatomy, 60
Articular Disk and
Ligaments, 61
Muscles, 63
Copyright © 2019, Elsevier Inc.

PARANASAL SINUSES, 66
Ethmoid, 67
Maxillary, 69
Sphenoid, 70
Frontal, 71
Osteomeatal Unit, 72
ORBIT, 73
Bony Orbit, 73
Soft Tissue Structures, 77
Optic Nerve, 79
Muscles of the Eye, 81
Lacrimal Apparatus, 84

13

14

CHAPTER 2 Cranium and Facial Bones

CRANIUM

Coronal suture

The cranium is composed of eight bones that surround
and protect the brain. These bones include the parietal
(2), frontal (1), ethmoid (1), sphenoid (1), occipital (1),
and temporal (2) (Figs. 2.2–2.5). The cranial bones are
composed of two layers of compact tissue known as the
internal (inner) and external (outer) tables. Located between the two tables is cancellous tissue or spongy
bone called diploe (Figs. 2.6–2.9). The base of the cranium houses three fossae called the anterior, middle, and
posterior cranial fossae. The anterior cranial fossa (frontal fossa) is composed primarily of the frontal bone,
ethmoid bone, and lesser wing of the sphenoid bone and
contains the frontal lobes of the brain. The middle cranial fossa (temporal fossa) is formed primarily by the
body of the sphenoid and temporal bones and houses the
pituitary gland, hypothalamus, and temporal lobes of
the brain. The posterior cranial fossa (infratentorial
fossa) is formed by the occipital and temporal bones and
contains the cerebellum and brainstem (Figs. 2.6 and
2.7). For additional details of the contents found within

Frontal bone
Parietal
bone

Supraciliary
arch

Glabella

Optic
canal

Sphenoid
bone

Sphenoid
bone
(greater
wing)

Superior
orbital fissure
Temporal
bone

Optic
strut

FIG. 2.2 Anterior view of skull.

Bregma

Coronal suture

Pterion
Sphenoparietal
suture

Frontal bone

Parietal bone

Parietomastoid
suture

Sphenofrontal
suture
Glabella
Ethmoid
bone
Sphenosquamosal
suture

Supraorbital
foramen

Sq

ua
m
id
ou
o
n
s
e
h ne
p
Temporal bone sutu
S bo

Asterion
Lambda

re

id
to s
as es
M roc
p

External auditory meatus
Styloid process

FIG. 2.3 Lateral view of skull.

Lambdoidal
suture
Occipital bone
External occipital
protuberance
(inion)

Occiptomastoid
suture

CHAPTER 2 Cranium and Facial Bones

15

Coronal suture

S

Frontal
bone

Parietal
eminence

Parietal
bone
Superior
orbital
fissure

Glabella

Temporal
bone

Supraciliary
arch
R

L

Ethmoid
bone

Sphenoid
bone
Zygoma

Inferior nasal
concha

Maxilla

Vomer

Mandible

FIG. 2.4 3D CT of anterior skull.
I
Parietal bone

S

Vertex

Coronal suture
Frontal
bone

Squamous
suture
Pterion
Lambdoidal
suture

Sphenofrontal
suture

Occipital
bone

Sphenoid
bone
Nasal bone
A
Ethmoid
bone

P
External
occipital
protuberance
Asterion

Zygomatic
arch

Parietomastoid
suture

Zygoma

Occipitomastoid
suture

Maxilla

Temporal
bone

Mandible

Mastoid
process

FIG. 2.5 3D CT of lateral skull.
I

CHAPTER 2 Cranium and Facial Bones

Internal
table

Diploë

External table

Ethmoid notch of
frontal bone
Orbital plate of
frontal bone

FRONTAL BONE

Crista galli

ETHMOID BONE

Anterior cranial fossa

Cribriform plate
Lesser wing of
sphenoid bone

Sella turcica

SPHENOID BONE
(greater wing)

Foramen rotundum

End of carotid
canal

Middle cranial fossa

Foramen ovale
Foramen lacerum

TEMPORAL BONE

Foramen spinosum
Internal auditory canal
Jugular foramen

Posterior cranial fossa

Mastoid foramen
Hypoglossal canal

OCCIPITAL BONE
Foramen magnum

Internal occipital protuberance

FIG. 2.6 Superior view of cranial fossae.

Ethmoid notch of
frontal bone

Crista
galli

A

Cribriform
plate

Orbital plate of
frontal bone

Middle
cranial
fossa

Anterior
cranial
fossa

Frontal bone

Sella turcica

Ethmoid bone
Foramen ovale

Lesser wing of
sphenoid bone

Foramen
spinosum

Sphenoid bone
(greater wing)
Foramen lacerum

Temporal bone

Petrous
portion of
temporal bone
Posterior
cranial
fossa

16

External table
Occipital
bone

Diploë

Clivus

P

Foramen
magnum

Internal table

FIG. 2.7 3D CT of cranial fossae, superior view.

CHAPTER 2 Cranium and Facial Bones
Meningeal grooves

Vertex

Sphenosquamosal suture
Parietal bone

Coronal suture

External table
Diploë

Sphenofrontal
suture

Internal table
FRONTAL BONE

Lambdoidal
suture
Sella turcica

Frontal sinus

Squamous suture

Crista galli
SPHENOID BONE

OCCIPITAL BONE

NASAL BONE
TEMPORAL BONE

ETHMOID BONE

Occipitomastoid suture
Internal auditory canal

MAXILLARY BONE

Hypoglossal canal

Clivus
Styloid process

VOMER

Sphenoid sinus
MANDIBLE
PALATINE BONE

FIG. 2.8 Lateral view of inner skull.

Frontal bone

S

Meningeal
vessels

Vertex

Internal
table

Diploë
Crista galli
External
table

Frontal sinus
P

A
Nasal bone

Ethmoid bone

Occipital
bone

Sphenoid bone
Vomer
Anterior
clinoid
process

Sella
turcica

Dorsum
sella

I

Internal
auditory
canal

External
occipital
protuberance

FIG. 2.9 3D CT of inner skull, lateral view.

17

CHAPTER 2 Cranium and Facial Bones

18
TABLE 2.1

by corresponding meningeal vessels and cerebral gyri and
sulci (Figs. 2.8 and 2.9). The parietal bones articulate with
the frontal, occipital, temporal, and sphenoid bones. The
superior point between the parietal bones is the vertex,
which is the highest point of the cranium (Figs. 2.9 and
2.10). Each parietal bone has a central prominent bulge on
its outer surface termed the parietal eminence (Fig. 2.4).
The width of the cranium can be determined by measuring
the distance between the two parietal eminences.

Contents of the Cranial Fossae

Fossa

Contents

Anterior cranial
fossa
Middle cranial
fossa

Frontal lobes of cerebrum; olfactory nerve (I)
Temporal lobes of cerebrum, pituitary gland,
cavernous sinus, trigeminal ganglion,
internal carotid artery, hypothalamus, and
the following cranial nerves: optic nerves
(II) and chiasm, oculomotor (III), trochlear
(IV), trigeminal (V), abducens (VI)
Cerebellum, pons, medulla oblongata, midbrain, and the following cranial nerves:
facial (VII), vestibulocochlear (VIII),
glossopharyngeal (IX), vagus (X),
accessory (XI), hypoglossal (XII)

Posterior cranial
fossa

Frontal Bone
The frontal bone consists of a vertical and a horizontal portion. The vertical or squamous portion forms the forehead
and anterior vault of the cranium (Figs. 2.2–2.5). The vertical portion contains the frontal sinuses, which lie on either
side of the midsagittal plane (Figs. 2.8, 2.9, 2.11, and 2.12).
Two elevated arches, the supraciliary arches, are joined to
one another by a smooth area termed the glabella (Figs. 2.2
and 2.4). The horizontal portion forms the roof over each
orbit, termed the orbital plate, and the majority of the anterior cranial fossa (Figs. 2.6, 2.7 and 2.13). Located in the
superior portion of each orbit is the supraorbital foramen,
or notch, which exists for the passage of the supraorbital
nerve (Figs. 2.2 and 2.11). Between the orbital plates is an
area termed the ethmoid notch, which receives the cribriform plate of the ethmoid bone (Figs. 2.6 and 2.7).

the cranial fossa, see Table 2.1. Each cranial bone is
structurally unique, and thus identification of the physical components can be challenging.

Parietal Bone
The two parietal bones form a large portion of the sides of
the cranium. Prominent markings and grooves that are
found within the inner surface of the cranium are formed
Parietal eminence
Coronal
suture

S

Vertex
Sagittal
suture

Lambdoidal
suture
Frontal
bone

A

P

Temporal
bone
Asterion
Occipital bone
Pterion
Occipitomastoid
suture

Sphenofrontal
suture

Squamous
suture

I

Parietomastoid
suture

FIG. 2.10 3D CT of lateral surface of cranium.

CHAPTER 2 Cranium and Facial Bones

Supraorbital foramen

19

Squamous portion
of frontal bone

S

Frontal
sinus

Nasal bone
Perpendicular
plate of ethmoid

Maxilla

I

FIG. 2.11 Coronal CT of frontal bone.

Frontal bone

Sella turcica

S

Dorsum sella

Frontal sinus
P

A
Nasal bone
Ethmoid air cells

Inferior
nasal
concha

Hard
palate

Sphenoid
sinus

FIG. 2.12 Sagittal CT reformat of frontal sinus.

I

Clivus of
occipital
bone

Occipital
bone

20

CHAPTER 2 Cranium and Facial Bones

A

Anterior clinoid process
of sphenoid bone

P

Frontal
sinuses

Temporal
bone

FIG. 2.13 Axial CT of orbital plates.

Orbital plate of
frontal bone

Occipital
bone

CHAPTER 2 Cranium and Facial Bones

Ethmoid Bone
The ethmoid bone is the smallest of the cranial bones
and is situated in the anterior cranial fossa. This cubeshaped bone can be divided into four parts: horizontal
portion, vertical portion, and two lateral masses (labyrinths) (Figs. 2.14–2.17). The horizontal portion, called
the cribriform plate, fits into the ethmoid notch of the
frontal bone (Figs. 2.6 and 2.7). This plate contains
many foramina for the passage of olfactory nerve fibers
(Figs. 2.14 and 2.15). The crista galli, a bony projection stemming from the midline of the cribriform plate,

projects superiorly to act as an attachment for the falx
cerebri, which is the connective tissue that anchors the
brain to the anterior cranial fossa (Figs. 2.16 and 2.17).
The vertical portion of the ethmoid bone, called the
perpendicular plate, projects inferiorly from the cribriform plate to form a portion of the bony nasal septum
(Fig. 2.16). The lateral masses (labyrinth) incorporate
thin-walled orbital plates (lamina papyracea), which
create a portion of the medial orbit (Figs. 2.15 and
2.17). Contained within the lateral masses are many
ethmoid air cells (ethmoid sinuses), one of the largest
being the ethmoid bulla (Figs. 2.14–2.16). Projecting

Perpendicular
plate
Cribriform
Crista galli
plane
Anterior
ethmoid
air cells
Horizontal
portion

Ethmoid
bulla

Olfactory
foramina
Posterior
ethmoid
air cells

FIG. 2.14 Superior view of ethmoid bone.

Orbital plate of ethmoid bone
(lamina papyracea)

A

Anterior ethmoid air cells
Cribriform
plate
Zygoma
Perpendicular
plate of
ethmoid
bone

Ethmoid
bulla

Posterior
ethmoid air
cells

Sphenoid
sinus

P
Dorsum sellae
of sphenoid bone

21

Anterior clinoid
process of sphenoid bone

FIG. 2.15 Axial CT of ethmoid bone.

22

CHAPTER 2 Cranium and Facial Bones

from the lateral masses are two scroll-shaped processes called the superior and middle nasal conchae
(turbinates) and the uncinate process. Between the
uncinate process and ethmoid bulla is a narrow
groove called the infundibulum, which is an important landmark of the paranasal sinuses (Figs. 2.16
and 2.17).

Crista galli

The naso-orbitoethmoid (NOE) complex is the union of
the ethmoid sinuses, frontal bone and sinuses, anterior
cranial fossa, orbits, and nasal bones. Fractures of the NOE
may cause symptoms that include nasal and forehead swelling, diplopia (double vision), and cerebrospinal fluid (CSF)
rhinorrhea (leakage of CSF into the nose).

Superior nasal concha

Ethmoid
air cells

Ethmoid
bulla
Infundibulum
Uncinate
process
Middle nasal concha
Lateral mass
(labyrinth)

Perpendicular plate
(vertical portion)

FIG. 2.16 Anterior view of ethmoid bone.

S

Internal
table

Diploë

External
table
Crista galli

Orbital plate
of frontal bone

Cribriform
plate
Orbital plate
of frontal bone
Orbital plate
of ethmoid bone
(lamina papyracea)

Infundibulum
Superior nasal
concha
Uncinate process
of ethmoid bone

Middle nasal
concha

Middle nasal
meatus

Bony nasal
septum

Inferior nasal
concha
Vomer

I

FIG. 2.17 Coronal CT of ethmoid bone with crista galli.

Inferior nasal
meatus

CHAPTER 2 Cranium and Facial Bones

23

termed sphenoid sinuses (Figs. 2.15 and 2.19). The anterior portion of the sella turcica is formed by the tuberculum sellae, and the posterior portion by the dorsum sellae. The dorsum sellae give rise to the posterior clinoid
processes (Figs. 2.18 and 2.20–2.22). The triangularshaped lesser wings attach to the superior aspect of the
body and form two sharp points called anterior clinoid
processes, which, along with the posterior clinoid processes, serve as attachment sites for the tentorium cerebelli (Figs. 2.18, 2.20, and 2.22). The optic canal is
completely contained within the lesser wing and provides passage of the optic nerve and ophthalmic artery

Sphenoid Bone
The butterfly-shaped sphenoid bone extends completely
across the floor of the middle cranial fossa (Figs. 2.6 and
2.7). This bone forms the majority of the base of the
skull and articulates with the occipital, temporal, parietal, frontal, and ethmoid bones. The main parts of the
sphenoid bone are the body, lesser wings (2), and greater
wings (2) (Fig. 2.18). Located within the body of the
sphenoid bone is a deep depression called the sella turcica, which houses the hypophysis (pituitary gland). Directly below the sella turcica are two air-filled cavities
Optic groove

Greater wing

Lesser wing

Optic canal
Anterior clinoid
process
Foramen rotundum
Foramen ovale

Tuberculum sellae
Body of
sphenoid bone

Foramen spinosum
Sella turcica

Dorsum
sellae

Carotid sulcus

FIG. 2.18 Superior view of sphenoid
bone.

Posterior clinoid process

Sella turcica

Dorsum sella

S

Tuberculum
sella
A

P

Ethmoid
sinuses

Sphenoid
sinus

Clivus

I

Posterior
arch of C1

Occipital
bone

FIG. 2.19 Sagittal CT reformat of sella turcica.
Tuberculum
sella
Superior orbital fissure

Anterior clinoid processes
Posterior clinoid process

Dorsum sellae
Sella turcica
(contains pituitary
gland)

Greater wing
Medial pterygoid plate
Lateral pterygoid plate
Pterygoid hamulus

Foramen
rotundum

FIG. 2.20 Lateral view of sphenoid bone.

24

CHAPTER 2 Cranium and Facial Bones
S
Parietal
bone

Posterior
clinoid
process

Foramen
lacerum

Temporal
bone
L
Dorsum
sella

R

Condylar
process of
mandible

I

FIG. 2.21 Coronal CT of dorsum sella.

A
Zygoma
Ethmoid
sinuses
Superior
orbital fissure

Sphenoid
sinus

Sella turcica
Optic
canal

Greater wing
of sphenoid
Anterior
clinoid
process

Lesser wing
of sphenoid

Dorsum sella
Posterior clinoid
processes

P

FIG. 2.22 Axial CT of anterior clinoid processes and sphenoid bone.

(Fig. 2.22). The optic canal is separated from the superior orbital fissure by a bony root termed the optic strut
(inferior root) (Fig. 2.2, see bony orbit). The superior
orbital fissure is a triangular-shaped opening located
between the lesser and greater wings that allows for the
transmission of the oculomotor, trochlear, abducens, and
ophthalmic division of the trigeminal nerves, as well as
the superior ophthalmic vein (Figs. 2.2, 2.22, 2.24, also
see bony orbit). The greater wings extend laterally from

the sides of the body and contain three paired foramina—rotundum, ovale, and spinosum—through which
nerves and blood vessels course (Figs. 2.6, 2.18, and
2.23–2.25; Table 2.2). Extending from the inferior surface of each greater wing is a pterygoid process, which is
divided into medial and lateral pterygoid plates. The
pterygoid plates serve as attachment sites for the pterygoid muscles used in movements of the lower jaw.
The medial section is longer and has a hook-shaped

CHAPTER 2 Cranium and Facial Bones
projection on its inferior end termed the pterygoid hamulus, which provides support for the gliding motion of the
tendon of the tensor veli palatine muscle as it opens the
eustachian tube (Figs. 2.20, 2.24, and 2.25). At the
base of the pterygoid process is the pterygoid (vidian)
canal, an opening for the passage of the petrosal nerve
(Figs. 2.23–2.25). The pterygoid processes articulate with

25

the palatine bones and vomer to form part of the nasal
cavity.
The sphenoid bone is considered the keystone of the
cranial bones because it is the only bone that articulates with all the other cranial bones.

Sphenoid
sinus

A

Ethmoid
sinuses

Pterygoid (vidian)
canal

Greater
wing of
sphenoid
bone

Foramen
spinosum

Foramen
ovale

Carotid
canal
R

L

Jugular
fossa

P

FIG. 2.23 Axial CT of sphenoid bone with foramina ovale and spinosum.

Superior orbital fissure

Lesser wing

Greater
wing

Body

Foramen
rotundum

Pterygoid
(vidian) canal
Pterygoid
hamulus

Lateral
pterygoid
plate

Medial
pterygoid
plate
Pterygoid
process

FIG. 2.24 Anterior view of sphenoid bone.

26

CHAPTER 2 Cranium and Facial Bones
S
Anterior clinoid
process of
sphenoid bone
Sphenoid
sinus

Greater wing of
sphenoid bone

Foramen
rotundum

Zygomatic
arch
R

L

Ramus of
mandible

Pterygoid
(vidian)
canal

Lateral
pterygoid
plate

Medial
pterygoid
plate

Pterygoid
process

I

FIG. 2.25 Coronal CT of sphenoid bone.

TABLE 2.2

Foramina and Fissures of the Skull

Bone

Foramen/Fissure

Major Structures Using Passageway

Frontal

Supraorbital foramen (or notch)
Frontal foramen (or notch)
Cribriform plate
Foramen rotundum
Foramen ovale
Foramen spinosum
Pterygoid canal
Optic canal
Superior orbital fissure

Supraorbital nerve and artery
Frontal artery and nerve
Olfactory nerve (I)
Maxillary branch of trigeminal nerve (V2)
Mandibular branch of trigeminal nerve (V3)
Middle meningeal artery
Petrosal nerve
Optic nerve (II) and ophthalmic artery
Ophthalmic vein and the following cranial nerves: oculomotor (III),
trochlear (IV), ophthalmic branch of trigeminal (V1), abducens (VI)
Maxillary branch of trigeminal nerve (V2)
Medulla oblongata and accessory nerve (XI)
Hypoglossal nerve (XII)
Internal carotid artery
Air in canal conducts sound to tympanic membrane
Vestibulocochlear nerve (VIII) and facial nerve (VII)
Facial nerve (VII)

Ethmoid
Sphenoid

Sphenoid and maxillary bone
Occipital
Temporal

Temporal and occipital bone

Inferior orbital fissure
Foramen magnum
Hypoglossal canal
Carotid canal
External auditory meatus
Internal auditory canal
Stylomastoid foramen and facial
nerve canal
Jugular foramen

Temporal, sphenoid, and
occipital bones

Foramen lacerum

Maxillary
Lacrimal with maxilla
Mandible

Infraorbital foramen
Lacrimal groove, nasolacrimal canal
Mental foramen

Internal jugular vein, glossopharyngeal nerve (IX), vagus nerve (X),
and accessory nerve (XI)
Fibrocartilage, internal carotid artery as it leaves carotid canal to enter
cranium, nerve of pterygoid canal and a meningeal branch from the
ascending pharyngeal artery
Infraorbital nerve and maxillary branch of trigeminal nerve (V2)
Lacrimal sac and nasolacrimal duct
Mental artery and nerve

CHAPTER 2 Cranium and Facial Bones

Occipital Bone
The occipital bone forms the posterior cranial fossa
and the inferoposterior portion of the cranium. On the
inferior portion of the occipital bone is a large oval
aperture called the foramen magnum located at the
junction of the brainstem and spinal cord (Fig. 2.26).
The occipital bone can be divided into four portions:
occipital condyles (2), basilar portion (1), and squamous portion (1) (Fig. 2.27). The occipital condyles
project inferiorly to articulate with the first cervical

Pterygoid
plate

27

vertebra (atlas), forming the atlantooccipital joint
(Figs. 2.28 and 2.29). Located obliquely at the base of
the condyles and anterolateral to the foramen magnum
are the hypoglossal canals through which the hypoglossal nerve (CN XII) courses (Figs. 2.8, 2.27, 2.28, and
2.30; Table 2.2). The basilar portion forms the anterior
margin of the foramen magnum and slopes superiorly
and anteriorly to meet with the dorsum sella of the
sphenoid bone to form the clivus (Figs. 2.8, 2.27, and
2.29–2.32). The squamous portion curves posterosuperiorly from the foramen magnum to articulate with the

Sphenoid bone
Zygomatic
arch
Squamous
portion

Clivus
Temporal
bone

Basilar portion
(clivus)

Hypoglossal
canal

Occipital
condyle

Foramen
magnum
Occipital
bone

Occipital
condyles

FIG. 2.26 Inferior surface of occipital bone and cranium.

Hypoglossal canal

Foramen magnum

FIG. 2.27 Lateroinferior aspect of occipital bone.

S

Jugular fossa

Temporal
bone
Occipital
condyle
Lateral
mass of
C1
(atlas)

External
occipital
protuberance
(inion)

I
Dens of C2
(odontoid process)

Atlantooccipital
joint

FIG. 2.28 Coronal CT reformat of occipital condyles.

28

CHAPTER 2 Cranium and Facial Bones
A

Pterygoid process
of sphenoid bone
Maxillary
sinus

Zygomatic
arch
Coronoid
process of
mandible

Ramus of
mandible
Styloid process
of temporal bone

Occipital
condyle

Atlantooccipital
joint

Clivus

Foramen
magnum
P

FIG. 2.29 Axial CT of occipital bone at level of foramen magnum and lateral condyles.

A
Ethmoid
air cells
Zygoma
Pterygopalatine
fossa

Sphenoid
sinus

Zygomatic
process of
temporal bone

Condyle of
mandible
Clivus
Hypoglossal
canal
Temporal
bone

Occipital
bone

Foramen
magnum
P

FIG. 2.30 Axial CT of occipital bone at level of clivus.

CHAPTER 2 Cranium and Facial Bones

S
Dorsum sellae of
sphenoid bone
Internal
occipital
protuberance

Sella turcica of
sphenoid bone
A

P

Sphenoid
sinus

External
occipital
protuberance (inion)

Clivus of
occipital bone

Squamous
portion of
occipital bone

Anterior arch
of C1

Foramen
magnum
Dens
of C2

I

Posterior arch
of C1

FIG. 2.31 Sagittal CT reformat of occipital bone.
S

A

P

Pituitary
gland

Squamous
portion of
occipital bone
Sphenoid
sinus

Clivus

Pons

I

Cerebellum

FIG. 2.32 Sagittal, T1-weighted MRI of occipital bone with clivus, post contrast enhancement.

29

CHAPTER 2 Cranium and Facial Bones

30

Inferior
orbital fissure

A

Petro-occipital fissure
Carotid canal

Foramen
rotundum

Auditory
(eustachian)
tube

Zygomatic
process

Mandibular
fossa

External
auditory
meatus

Jugular
fossa

Sigmoid
sinus

P

Internal occipital
protuberance

Mastoid
air cells

FIG. 2.33 Axial CT of occipital bone with internal occipital protuberance.

parietal and temporal bones (Fig. 2.3). Located on the
inner surface of the squama is a bony projection termed
the internal occipital protuberance, which marks the
site where the dural venous sinuses converge (Figs. 2.6,
2.31, and 2.33). The external occipital protuberance is
a midline projection on the external surface of the
squamous part of the occipital bone. The highest point
of the external occipital protuberance is termed the inion (Figs. 2.27 and 2.31).

Squamous
portion

External
auditory meatus

Zygomatic
process

Articular eminence

Temporal Bone
The two temporal bones contain many complex and
important structures. They form part of the sides and
base of the cranium, and together with the sphenoid
bone, they create the middle cranial fossa (Figs. 2.3
and 2.6). The temporal bone can be divided into four
portions: squamous, tympanic, mastoid, and petrous
(Figs. 2.34 and 2.35). The thin squamous portion
projects upward to form part of the sidewalls of the
cranium (Fig. 2.3). Extending from the squamous portion is the zygomatic process, which projects anteriorly to the zygoma of the face to form the zygomatic
arch (Figs. 2.23, 2.25, 2.30, 2.34, and 2.36). At the
base of the zygomatic process is the articular eminence
that forms the anterior boundary of the mandibular
fossa. The mandibular fossa is the depression that articulates with the condyloid process of the mandible,

Mandibular fossa
Styloid process

Mastoid portion
Mastoid process
Tympanic portion

FIG. 2.34 Lateral view of temporal bone.

creating the temporomandibular joint (Figs. 2.34 and
2.37). The tympanic portion lies below the squama
and forms the majority of the external auditory meatus (Figs. 2.33–2.35 and 2.37). Just posterior to the
tympanic portion is the mastoid portion, which has a
prominent conical region termed the mastoid process
(Figs. 2.34 and 2.37–2.39). The mastoid process encloses the mastoid air cells and mastoid antrum. The
mastoid antrum is located on the anterosuperior portion of the mastoid process. It is an air-filled cavity

CHAPTER 2 Cranium and Facial Bones

31

Tympanic portion
Cochlea

Temporal bone
(petrous portion)

Tympanic membrane

Head of malleus

Stapes

Tragus
External
auditory meatus

Cochlear nerve
(CN VIII)

Incus
Vestibular nerve
(CN VIII)

Auricle (pinna)
Facial nerve
(CN VII) in
facial canal

Petrous
portion

Mastoid air cells

Internal
auditory canal
Internal
auditory
canal

Ampulla of superior
semicircular duct

Groove for
sigmoid sinus
Vestibular ganglion

Jugular foramen

Posterior Superior Lateral
(anterior)
Semicircular canals

FIG. 2.35 Superior view of petrous portion of temporal bone with middle and inner ear.

Zygoma
Zygomatic
arch

Carotid
canal
Jugular
foramen

Zygomatic
process of
temporal
bone
Styloid
process
Temporal
bone

FIG. 2.36 Inferior surface of temporal bone and cranium.

that communicates with the middle ear (tympanic
cavity) (Figs. 2.37–2.39). The petrous portion of the
temporal bone is pyramidal in shape and situated at
an angle between the sphenoid and occipital bones
(Fig. 2.35). The posterior surface of the petrous pyramid forms the anterior bony limit of the posterior
fossa (Fig. 2.6). Near the center of this surface is the

opening to the internal auditory canal, which transmits the seventh and eighth cranial nerves (Figs. 2.35
and 2.39). Other openings associated with the posterior surface of the petrous pyramid are the jugular
foramen and the carotid canal, which provide passage
for the internal jugular vein and the internal carotid
artery (Figs. 2.36 and 2.38–2.41; Table 2.2). An
enlargement of the jugular foramen is the jugular
fossa (Fig. 2.42). Continuous in front of the jugular
foramen is the petro-occipital fissure that separates
the petrous portion of the temporal bone from the
foramen magnum of the occipital bone (Fig. 2.40).
The carotid canal courses superiorly at its lower segment, then changes direction and is seen coursing
posterior to anterior (Figs. 2.33 and 2.38–2.41. See
also Chapter 3, internal carotid arteries). Superior to
the carotid canal is an indentation on the petrous
portion called Meckel’s cave (Fig. 2.41). Also known
as the trigeminal cistern, Meckel’s cave is located between two layers of dura and encloses the trigeminal
ganglion. It is filled with CSF and is continuous with
the pontine cistern and subarachnoid space (see also
trigeminal nerve in Chapter 3). Between the apex of
the petrous pyramid, the body of the sphenoid bone,
and the basilar portion of the occipital bone is a jagged slit termed the foramen lacerum, which contains
cartilage and allows the internal carotid artery to

32

CHAPTER 2 Cranium and Facial Bones

enter the cranium (Figs. 2.6 and 2.40; Table 2.2). The
inferior surface of the petrous pyramid gives rise to the
long slender styloid process that is attached to several
muscles of the tongue and ligaments of the hyoid bone
(Figs. 2.8, 2.29, and 2.34). The stylomastoid foramen
is situated between the mastoid process and the styloid
process. This foramen constitutes the end of the facial
nerve canal (Figs. 2.38, 2.42, and 2.50–2.58; Table
2.2). The interior of the petrous pyramid houses the
delicate middle and inner ear structures.

A basilar skull fracture is a fracture of the bones that form
the base (floor) of the skull and typically involves the occipital, sphenoid, temporal, and/or ethmoid bones. Basilar skull
fractures can cause tears in the meninges, the membranes surrounding the brain. Subsequent leakage of CSF into the nasopharynx may cause the patient to experience a salty taste. Other
clinical signs of a basilar skull fracture may include bruising behind the ears or around the eyes; loss of hearing, smell, or vision;
and possible nerve damage resulting in weakness of the face.

Mandibular
fossa

S

Mastoid antrum

Articular
eminence
A

P

Mastoid
air cells in
mastoid
process

I

Mandibular
condyle

External
auditory meatus

FIG. 2.37 Sagittal CT reformat of temporal bone.

Mastoid antrum

Tympanic cavity (middle ear)
Stylus in facial canal
Carotid canal

Mastoid
process
Bony part of
eustachian tube
Stylus in
stylomastoid foramen

FIG. 2.38 Coronal view of temporal bone.

Mastoid air cells

CHAPTER 2 Cranium and Facial Bones

Malleus

33

Sphenoid
sinus

A

Carotid
canal

Mastoid
air cells

Mastoid
antrum

Vestibule

P

Internal auditory
canal

FIG. 2.39 Axial CT of temporal bone with internal auditory canal (IAC).

A
Nasolacrimal
duct

Pterygoid
process

Pterygomaxillary
fissure

Zygomatic
arch

Clivus

Foramen
ovale

Eustachian
(auditory) tube

Foramen
spinosum

Mandibular
condyle

Foramen
lacerum
R

L
External
auditory
meatus

Carotid
canal
Petrooccipital
fissure

Mastoid
air cells

Jugular
foramen

Internal
occipital
protuberance

Occipital
bone
P

FIG. 2.40 Axial CT of temporal bone with foramen lacerum, jugular foramen, and carotid canal.

34

CHAPTER 2 Cranium and Facial Bones

Posterior
clinoid
process
Temporal
bone

Sphenoid
sinus

Meckel’s
cave

Condylar
process of
mandible

Sphenoid
bone

Carotid
canal

FIG. 2.41 Coronal CT reformat of temporal bone with Meckel’s cave.

S
Semicircular
canals of
inner ear

Jugular
fossa

Facial nerve
canal

Mastoid
air cells

Mastoid
process

Hypoglossal
canal

Stylomastoid
foramen

Occipital
condyle

I

FIG. 2.42 Coronal CT reformat of stylomastoid foramen.

CHAPTER 2 Cranium and Facial Bones

Structures of the External, Middle,
and Inner Ear
The structures of the ear can be divided into three main
portions: external, middle, and inner (Figs. 2.43–2.59).
The external ear consists of the auricle and the external auditory meatus. The external auditory meatus is a
External ear

Middle ear

35

sound-conducting canal that terminates at the tympanic
membrane of the middle ear (Figs. 2.40 and 2.43).
The narrow, air-filled middle ear, or tympanic cavity,
communicates with both the mastoid antrum and the nasopharynx. Air is conveyed from the nasopharynx to the
tympanic cavity through the eustachian tube (auditory
tube) (Figs. 2.40 and 2.43). The middle ear consists of the
Inner ear
Semicircular canals

Malleus

Oval
window

Auricle
(pinna)

Posterior Superior
(anterior)
Temporal bone
(petrous portion)

Lateral

Scutum

tympan
Tegman
i

Vestibular complex
Cochlea
Internal auditory canal
Vestibulocochlear nerve
(cranial nerve VIII)
Bony labyrinth
of inner ear

Cartilage

Stapes

Tympanic
membrane

External
auditory meatus

Incus

A

Round
Internal window
jugular vein

Eustachian
(auditory) tube
To pharynx

Incus

Epitympanum

Prussak space

Stapes footplate/oval
window

Scutum
Malleus

Mesotympanum

Tympanic
membrane

Hypotympanum
Eustachian tube

B

FIG. 2.43 (A) Orientation of the external, middle, and inner ear in coronal view. (B) Coronal view of auditory ossicles and tympanic cavity.
Superior (anterior)
semicircular canal
Cochlea

Vestibule

Posterior
semicircular
canal

Oval window

Round window

Lateral
semicircular canal

Basilar turn of cochlea

FIG. 2.44 Bony labyrinth.

36

CHAPTER 2 Cranium and Facial Bones

Clivus

A

Cerebellopontine
angle cistern

Cochlea

CN VII

Vestibule
CN VIII
R

L
Semicircular
canal

Internal
auditory
canal

P

FIG. 2.45 Axial, T2-weighted MRI of inner ear.

A

Cochlea
Inner ear

Middle ear
R

L

External
auditory
meatus
Vestibule
Semicircular
canal

P

FIG. 2.46 Axial CT of temporal bone at level of external auditory meatus.

CHAPTER 2 Cranium and Facial Bones
Ampulla
Superior semicircular canal and duct
Dura mater

Posterior semicircular
canal and duct

Endolymphatic sac
Endolymphatic duct in
vestibular aqueduct
Utricle

Lateral semicircular
canal and duct

Saccule

Otic capsule
Stapes in oval
window

Scala vestibuli

Incus

Cochlear
duct
Scala
tympani

Malleus
Tympanic cavity
External auditory meatus

Tympanic membrane

Cochlear aqueduct
Vestibule

Round window

Otic capsule

Eustachian (auditory) tube

FIG. 2.47 Membranous labyrinth.

Pons

A

Endolymphatic sac

Cochlea
Semicircular
canal

R

L
Fourth
ventricle

Cerebellum

P

FIG. 2.48 Axial, T2-weighted MRI with enlarged endolymphatic sac.

37

38

CHAPTER 2 Cranium and Facial Bones
Squamous portion
of temporal bone

A

R

L

Mastoid
air cells

Occipitomastoid
suture

Sigmoid
sinus

P

Superior
semicircular
canal

Petrous portion
of temporal bone

FIG. 2.49 Axial CT of superior semicircular canal.

tympanic membrane and three auditory ossicles (malleus,
incus, and stapes) (Fig. 2.43B). The tympanic membrane
transmits sound vibrations to the auditory ossicles. The
auditory ossicles, which are suspended in the middle ear,
conduct sound vibrations from the tympanic membrane to
the oval window of the inner ear (Figs. 2.43, 2.49–2.59).
The middle ear can be subdivided into the epitympanum, mesotympanum, and hypotympanum. The epitympanum, also called the attic, is located superior to the
tympanic membrane and contains the head of the malleus
and body of the incus. It communicates with the mastoid
air cells through a narrow opening called the aditus ad
antrum (mastoideum), a potential route for the spread of
infection from the middle ear to the mastoid air cells
(Figs. 2.50 and 2.51). The roof of the epitympanum is
separated from the middle cranial fossa by a thin layer of
bone termed the tegmen tympani. Two other important
landmarks of the epitympanum include the scutum and
the Prussak space. The scutum is a sharp, bony spur on
the lateral wall of the tympanic cavity and the superior
wall of the external auditory meatus (Figs. 2.43B and
2.57). The scutum provides the superior attachment site
for the tympanic membrane. The Prussak space (lateral

epitympanic recess) is bordered laterally by the tympanic
membrane, superiorly by the scutum, medially by the
neck of the malleus, and inferiorly by the lateral process
of the malleus (Figs. 2.43 and 2.57). The boundaries of
the Prussak space limit the spread of infection to other
compartments of the middle ear.
The mesotympanum is the portion of the middle ear that
is medial to the tympanic membrane and contains the stapes, the long process of the incus, the handle of the malleus,
and the oval and round windows (Figs. 2.43B and 2.56).
The hypotympanum is the portion of the middle ear
that is located inferior to the lower border of the tympanic membrane and is the site of the tympanic opening
for the eustachian tube (Figs. 2.43B and 2.49–2.59).
The inner ear, or bony labyrinth, contains the vestibule and semicircular canals, which control equilibrium
and balance, and the cochlea, which is responsible for
hearing (Figs. 2.43–2.48). The vestibule is a small bony
compartment located between the semicircular canals
and the cochlea. Two openings of the vestibule are the
oval window (Fig. 2.44) for the footplate of the stapes
and the vestibular aqueduct, which contains the endolymphatic duct (Fig. 2.47). The semicircular canals are

CHAPTER 2 Cranium and Facial Bones
continuous with the vestibule and are easily identified
because of their three separate passages (superior [anterior], posterior, and lateral) that are at right angles to
each other (Figs. 2.42–2.44). The three interconnected
semicircular canals are lined with microscopic hairs
called cilia and are filled with fluid known as endolymph. Every time the position of the head changes, the

Epitympanum

fluid moves against the cilia, creating a kind of motion
sensor. This helps the brain create a sense of balance.
The cochlea is a spiral-shaped structure with a base that
lies on the internal auditory canal (Figs. 2.43 and 2.45).
Located within the basilar turn of the cochlea is the
round window, which allows the fluid of the inner ear to
move slightly for propagation of sound waves and nerve

Malleus

A

Facial nerve (CN VII)
canal (labyrinthine
segment)

Prussak
space
Aditus ad antrum
mastoideum

R

L
Internal
auditory canal
(IAC)

Mastoid
antrum

Lateral
semicircular
canal

P

Posterior
semicircular
canal

Vestibule

FIG. 2.50 Axial CT of lateral semicircular canal.

A

Malleus
Facial nerve
canal (tympanic
segment)

Prussak
space
Incus

Cochlea
(first turn)
R

L
Internal
auditory canal
(IAC)

Aditus
ad antrum
mastoideum
Mastoid
antrum

Lateral
semicircular
canal

P

39

Vestibule

FIG. 2.51 Axial CT of malleus and incus.

40

CHAPTER 2 Cranium and Facial Bones

impulses to be sent to the brain (Figs. 2.44 and 2.47).
Within the bony labyrinth is a complicated system of
ducts called the membranous labyrinth, which is filled
with endolymph, a fluid that helps with the propagation
of sound waves (Fig. 2.47). Extending from the vestibule
is a slender endolymphatic duct that terminates as the
endolymphatic sac, which is located between two dural

layers on the posterior wall of the petrous pyramid
(Figs. 2.47 and 2.48). The endolymphatic duct and sac
are thought to be responsible for the reabsorption of endolymph and may contribute to vestibular dysfunction.
Figs. 2.49–2.59 provide sequential computed tomography (CT) images through the external, middle, and inner
ear in the axial and coronal planes, respectively.
(Text continues on page 44)

Malleus

Stapes

A

Cochlea

Incus

R

L
Internal
auditory canal
(IAC)

Facial
nerve
canal
(mastoid
segment)
Oval
window

P

Posterior
semicircular
canal

FIG. 2.52 Axial CT of auditory ossicles.

A

Tensor tympani
muscle
Eustachian
tube

Malleus

Carotid
canal
R

L
Cochlea
(basal
turn)

External
auditory
meatus
(EAM)
Facial nerve
canal (mastoid segment)

FIG. 2.53 Axial CT of cochlea.

P

Round
window

CHAPTER 2 Cranium and Facial Bones
A

Tympanic membrane

Condyloid
process of
mandible
(condyle)

Hypotympanum

External
auditory
meatus
(EAM)

R

L
Jugular
foramen

Mastoid
air cells

P

Occipital
bone

Facial nerve
canal (mastoid segment)

FIG. 2.54 Axial CT of tympanic membrane.

S

Mastoid
antrum

Lateral
semicircular
canal

Posterior
semicircular canal
Facial nerve canal
(mastoid segment)
Stylomastoid
foramen

R

L
Occipital
condyle
Hypoglossal
canal

C1

Mastoid tip

I

Jugular
foramen

FIG. 2.55 Coronal CT reformat of semicircular canals.

41

CHAPTER 2 Cranium and Facial Bones

42

Mastoid
antrum

S

Lateral
semicircular
canal

Vestibule
Internal
auditory
canal (IAC)
Round
window

Facial nerve
canal
(tympanic segment)
L

R
External
auditory
meatus
(EAM)

Mesotympanum

I

FIG. 2.56 Coronal CT reformat of vestibule.
Squamous
portion of
temporal bone

Epitympanum

S

Incus

Superior
semicircular
canal

Oval
window
Internal
auditory
canal (IAC)
Basal turn
of cochlea

Prussak
space
R

L

Scutum

Hypotympanum

External
auditory
meatus
(EAM)

Facial
Stapes
nerve canal
(tympanic segment)

I

Tympanic
membrane

Tympanic
annulus

FIG. 2.57 Coronal CT reformat of IAC.

CHAPTER 2 Cranium and Facial Bones
Tegmen
tympani

Incus

S

43

Neck of
malleus
Facial nerve
canal
(tympanic segment)

Facial nerve
canal
(labyrinthine segment)

R

L

External
auditory meatus
(EAM)

Malleus

I

Cochlea

Carotid
canal

FIG. 2.58 Coronal CT reformat of EAM.
Tegmen
tympani

Malleus Geniculate ganglion
of facial nerve
head

S

Mesotympanum
First turn
of cochlea
L

R
Epitympanum
External
auditory
meatus

Anterior
scutum

Tympanic Hypotympanum
membrane

I

FIG. 2.59 Coronal CT reformat of cochlea.

Second turn
of cochlea

Carotid
canal

44

CHAPTER 2 Cranium and Facial Bones

Meniere disease is a disorder of the membranous
labyrinth that results from a failure of the mechanism
controlling the production and elimination of endolymph. In
advanced cases, there is an increased accumulation of endolymph volume, resulting in an abnormal distention of the
membranous labyrinth (endolymphatic hydrops). Meniere
disease is most common in middle age and may become bilateral in up to 50% of affected patients. Symptoms include
episodic vertigo accompanied by nausea, fluctuating hearing
loss, and a feeling of fullness in the affected ears. The success
of surgical intervention in relieving Meniere disease depends
a great deal on the ability to image and evaluate the vestibular
aqueduct and endolymphatic duct and sac.
Cholesteatomas are epidermoid cysts of the middle ear
that can be acquired or congenital. The lumen of the cyst
is filled with debris. As a cholesteatoma enlarges, it destroys the
ossicles and adjacent bony structures. Cholesteatomas are usually associated with chronic infection, aural discharge, and conductive or mixed deafness. The Prussak space is the most common site of acquired cholesteatomas within the tympanic cavity.

Sutures
The cranial bones are joined by four main articulations
termed sutures. The squamous suture, which is located
on the side of the cranium, joins the squamous portion
of the temporal bone to the parietal bone. The coronal
Coronal
suture

Sphenoparietal
suture

suture runs across the top of the cranium and is the
articulation between the frontal and parietal bones. The
sagittal suture provides the articulation between the
parietal bones along the midsagittal plane. The lambdoidal suture is located posterior in the cranium and
joins the occipital and parietal bones (Figs. 2.3 and
2.60–2.63). Sutures corresponding to the mastoid portion of the temporal bone include the occipitomastoid
suture between the occipital bone and mastoid portion
of the temporal bone and the parietomastoid suture
between the parietal bone and mastoid portion of the
temporal bone. The asterion is a point on the skull corresponding to the posterior end of the parietomastoid
suture (Figs. 2.3 and 2.60). Sutures corresponding to the
sphenoid bone include the sphenosquamosal suture between the sphenoid bone and squamous portion of the
temporal bone, the sphenofrontal suture between the
greater wing of the sphenoid bone and the frontal bone,
and the sphenoparietal suture located between the
greater wing of the sphenoid bone and the parietal
bone. The region surrounding the sphenoparietal suture
where the parietal, sphenoid, temporal, and frontal
bones meet is termed the pterion, an important landmark because it is considered the weakest part of the
skull and is also the site of the anterolateral (sphenoid)
fontanel in neonates (Figs. 2.3 and 2.60). The frontal
(metopic) suture divides the frontal bone into halves as
it extends from the anterior fontanel or sagittal suture
to the nasion in infants and children and typically disappears by the age of 6 (Fig. 2.64).

Temporal bone

Vertex

Sagittal
suture

Parietal
bone

Frontal bone

Sphenofrontal
suture

Lambdoidal
suture
Pterion
Occipital
bone
Sphenosquamosal
suture

Squamous Parietomastoid
suture
suture

Occipitomastoid
suture

FIG. 2.60 3D CT of lateral surface of cranium.

Asterion

CHAPTER 2 Cranium and Facial Bones
A

Sphenoid
bone

Sphenosquamosal
suture
Temporal
bone
R

L

Mastoid
process

Clivus

Foramen
magnum

Occipital
bone

P

Occipitomastoid
suture

FIG. 2.61 Axial CT of occipitomastoid suture.
A

Frontal
bone

Squamous
suture
Temporal
bone
L

R
Petrous
portion of
temporal
bone

Mastoid
air cells

P
Internal
occipital
protuberance

Occipital
bone

Lambdoidal
suture

FIG. 2.62 Axial CT of lambdoidal suture.

45

CHAPTER 2 Cranium and Facial Bones

46

A

Frontal bone

Coronal
suture

L

R

Squamous
suture

Squamous
portion of
temporal
bone

Occipital
bone

P Lambdoidal
suture

FIG. 2.63 Axial CT of coronal suture.

The sutures in neonates are not fully closed, allowing
for growth of the head after birth. Craniosynostosis,
which is the result of premature ossification of one or more of
the cranial sutures, causes abnormal growth of the cranium
and can limit the growth of the brain.

The pterion is known as the weakest part of the skull and
is located over the anterior division of the middle meningeal artery. A severe blow to the side of the head causing a
fracture and rupture of the middle meningeal artery may result
in an epidural hematoma. A favored site of access for performing a bur hole to drain the hematoma is at the pterion.

CHAPTER 2 Cranium and Facial Bones

Fontanels
Within the neonatal cranium are six areas of incomplete
ossification called fontanels. The largest is the anterior
fontanel located at the junction of the upper parietal and
frontal bones termed the bregma (Fig. 2.64). This fontanel remains open until the age of 2. Located at the
lambda, the junction of the parietal and occipital bones
is the posterior fontanel (Fig. 2.65). The posterior fontanel typically closes between the first and third months
after birth. On the sides of the cranium are four
additional fontanels, two anterolateral (sphenoid) and
two posterolateral (mastoid) (Figs. 2.65 and 2.66). The

Anterior fontanel
(bregma)

S

anterolateral fontanels are located between the parietal
and greater wing of the sphenoid bones. The posterolateral fontanels are located at the junction of the occipital,
temporal, and parietal bones. The anterior and posterolateral fontanels ossify at approximately 2 years of age,
whereas the posterior and anterolateral fontanels close
between 1 and 3 months after birth.

Bulging of the anterior fontanel may indicate increased
intracranial pressure, whereas a sunken fontanel may
indicate dehydration.

Sagittal suture

Coronal
suture
R

L

Frontal (metopic suture)

47

I

FIG. 2.64 3D CT of infant cranium, anterior view.

CHAPTER 2 Cranium and Facial Bones
Anterolateral fontanel
S
Coronal suture
(sphenoid)

Parietal
bone
Fro
n
bon tal
e

48

Posterior
fontanel
(lambda)

A

P
Lambdoidal
suture
Posterolateral
fontanel
(mastoid)

Temporal
bone

Occipitomastoid
suture

Sphenoid
bone

Sphenosquamosal
suture

I

Squamous
suture

Occipital
bone

FIG. 2.65 3D CT of 17-week-old infant cranium, lateral view.

Anterior
fontanel (bregma)

Sagittal
suture

Coronal
suture

Parietal bone

Frontal
bone

al
por
Tem one
b

Frontal
(metopic) suture

Nasion

Sphenoid
bone

Anterolateral
fontanel (sphenoid)

FIG. 2.66 3D CT of 17-week-old infant cranium, oblique view.

CHAPTER 2 Cranium and Facial Bones

49

FACIAL BONES
The face is made up of 14 facial bones. The facial bones
can be difficult to differentiate because of their relatively
small size and irregular shape. They consist of the nasal

(2), lacrimal (2), palatine (2), maxilla (2), zygoma (2),
inferior nasal conchae (2), vomer (1), and mandible (1)
(Figs. 2.67–2.85).

Frontal
bone

Frontal process
of maxilla
Nasal
bones

Superior
orbital
fissure

Lacrimal bone

Zygoma

Bony
nasal
septum

Ethmoid bone

Inferior
orbital
fissure
Perpendicular
plate of ethmoid

Zygomatic
process of
maxilla
Maxilla

Vomer

Infraorbital foramen
Inferior nasal concha

Alveolar
process
of maxilla

Anterior nasal spine
(acanthion)
Mandible

Alveolar
process
of mandible

FIG. 2.67 Anterior view of facial

bones.

Mental protuberance

l
nta
Fro ne
bo
Parietal
bone

Lacrimal bone

Ethmoid bone

l
sa
Naone
b

id
eno
Sph one
b

Lacrimal groove
Anterior nasal
spine
(acanthion)
Temporal
process
of zygoma

Zygoma

Zygomatic
arch
Occipital
bone

Maxilla

Zygomatic
process of
temporal
bone

Alveolar
process

External auditory meatus
Mandible

Mandibular condyle
Angle (gonion)

Mental foramen

Coronoid
process

Mandibular
notch

FIG. 2.68 Sagittal view of facial

bones.

50

CHAPTER 2 Cranium and Facial Bones
Hard palate
Horizontal portion
of palatine bone

Palatine process
of maxilla

Zygoma

A

Temporal
process of
zygoma

Zygomatic
arch
R

L
Zygomatic
process of
the temporal
bone

Pterygoid
process of
sphenoid
bone

Temporal
bone

Condyloid
process of
mandible

Mastoid
process

Clivus of
occipital
bone

P

C1

Occipital
bone

FIG. 2.69 3D CT of inferior surface of cranial bones with mandible disarticulated.

Nasal Bones
The two nasal bones form the bony bridge of the nose
and articulate with four bones: the frontal and ethmoid
bones of the cranium and the opposite nasal bone and
maxilla (Figs. 2.67, 2.68, 2.70, 2.71, and 2.73).

Lacrimal Bones
Posterior to the nasal bones and maxilla are the lacrimal
bones, which are situated on the medial wall of each
orbit (Fig. 2.70). The junction between the lacrimal
bones and the maxillae forms the lacrimal groove,
which accommodates the lacrimal sacs that are part
of the drainage route for excess lacrimal fluid (tears)
(Figs. 2.67, 2.68, 2.70, and 2.71).

Palatine Bones
The palatine bones are slightly L-shaped and are located
in the posterior aspect of the nasal cavity between the
maxilla and the pterygoid process of the sphenoid bone

(Fig. 2.70). The palatine bones consist of a horizontal
portion and a vertical portion. The horizontal portion
of the palatine bones joins anteriorly with the palatine
process of the maxilla to form the hard palate (Figs. 2.8,
2.69, 2.74, and 2.75). The vertical portion extends to
form a segment of the lateral wall of the nasal cavity
and the medial wall of the orbit (Fig. 2.70). The pterygopalatine fossa is a gap between the pterygoid process
of the sphenoid bone, maxilla, and palatine bones. The
pterygopalatine fossa contains the maxillary nerve V2
(second division of the trigeminal nerve), the pterygopalatine ganglion, and the third part of the maxillary
artery (Figs. 2.30, 2.70, and 2.77).

Maxillary Bones
The largest immovable facial bones are the maxillary
bones, which fuse at the midline to form a pointed process termed the anterior nasal spine (Figs. 2.68, 2.70, and
2.71). An opening on the anterior aspect of the maxilla is
the infraorbital foramen, which transmits the infraorbital

CHAPTER 2 Cranium and Facial Bones
S
Orbital plate
of ethmoid bone

Frontal sinus
Orbital plate
of frontal bone

Optic canal
Palatine
bone (vertical portion)

Nasal bone
Lacrimal bone

Sphenoid bone

Lacrimal groove
Frontal process
of maxilla
Uncinate process
of ethmoid bone

Sella turcica
of sphenoid
bone
P

A

Foramen
rotundum

Infraorbital canal

Pterygopalatine
fossa

Inferior nasal
concha
Anterior nasal
spine

Palatine bone
(vertical portion)

Maxillary sinus
Alveolar process
of maxilla

Pterygoid plate
of sphenoid
bone
I

FIG. 2.70 Sagittal view of orbit and facial bones.

Temporal
process of
zygoma

Frontal
bone

Lacrimal
bone

Lacrimal
groove

Temporal
bone

Nasal bone

Zygomatic
process of
temporal bone

Frontal process
of maxilla

Zygomatic
arch

Maxilla

Anterior
nasal spine

Ramus of
mandible

Alveolar process
of maxilla

Zygoma

Zygomatic
process of
maxilla

Maxillary
sinus

Mental
foramen

Mandible

FIG. 2.71 3D CT of oblique aspect of facial bones.

51

CHAPTER 2 Cranium and Facial Bones

52

S

Frontal
bone
Crista
galli

Perpendicular
plate of ethmoid

Middle
nasal
concha

Infraorbital
foramen

Zygoma

Maxillary
sinus

Middle
nasal
meatus

Inferior
nasal concha

Zygomatic
process
of maxilla

Vomer
Alveolar
process
of maxilla

Maxilla

Inferior nasal
meatus

Palatine process
of maxilla

I

FIG. 2.72 Coronal CT of maxilla and zygoma.

S

Frontal
bone
Frontal
sinus
Nasal bone
Perpendicular
plate of ethmoid
bone

Frontal
process
of maxilla
I

FIG. 2.73 Coronal CT of nasal bones.

CHAPTER 2 Cranium and Facial Bones
Zygoma

Palatine process
of maxilla
Horizontal
portion of
palatine bone
Zygomatic
arch

53

form the alveolar process, which accepts the roots of the
teeth (Figs. 2.67, 2.71, 2.75, and 2.76). The palatine
process of the maxilla extends posteriorly to form threefourths of the hard palate. The posterior one-fourth of
the hard palate is created by the horizontal portion of the
palatine bones (Figs. 2.69, 2.74 and 2.75).

Zygomatic Bones
Temporal
bone
Foramen
magnum
Occipital
bone

FIG. 2.74 Inferior view of facial bones and hard palate.

nerve and blood vessels (Figs. 2.67 and 2.72). The maxillary bones contain the large maxillary sinuses and four
processes: the frontal process, zygomatic process, alveolar process, and palatine process (Figs. 2.67 and 2.72–
2.76). The frontal and zygomatic processes project
to articulate with the frontal bones of the cranium and
the zygomatic bones of the face (Figs. 2.71–2.73). The
inferior border of the maxilla has several depressions that

A

The zygomatic bones (zygoma or malar) create the
prominence of the cheek and contribute to the lateral
portion of the bony orbit (Figs. 2.67, 2.71, 2.72, 2.77,
and 2.78). They articulate with the maxilla and temporal, frontal, and sphenoid bones. The temporal process
of the zygomatic bone extends posteriorly to join the
zygomatic process of the temporal bone to form the zygomatic arch (Figs. 2.68, 2.69, 2.71, 2.74, and 2.77).
Le Fort fractures are a result of direct anterior facial
injuries. They are classified into three groups according
to the facial bones that are traumatized. Type I: The alveolar
process of the maxilla and the hard palate are separated from
the superior part of the skull. Type II: The alveolar, zygomatic,
and frontal processes of the maxilla along with the nasal
bones are separated from the frontal and zygomatic bones.
Type III: Virtually the entire facial skeleton, including the maxillae, nasal bones, and zygomatic bones, is separated from the
frontal bone above it.

Palatine process of Alveolar process
maxilla (hard palate)
of maxilla

Pterygoid
process of
sphenoid
bone

Horizontal
portion
of palatine
bone
(hard palate)

R

L

P

Styloid process
of temporal bone

Mandible

FIG. 2.75 Axial CT of hard palate.

CHAPTER 2 Cranium and Facial Bones

54

A

Alveolar process
of maxilla

R

L

Ramus of
mandible

Pterygoid process of
sphenoid bone

P

FIG. 2.76 Axial CT of alveolar process of maxilla.

Inferior
nasal concha

Nasolacrimal
duct
Maxilla
A

Zygomatic
process
of maxilla

Maxillary
sinus

Zygoma
Temporal process
of zygoma
Zygomatic
arch

Pterygoid process
of sphenoid bone

Pterygomaxillary
fissure
Pterygopalatine
fossa
Mandibular
condyle
Occipital
bone
Nasal septum

P

Foramen
magnum of
occipital bone

FIG. 2.77 Axial CT of facial bones.

CHAPTER 2 Cranium and Facial Bones

A

Nasal bone
Frontal process
of maxilla

Lacrimal bone

Anterior
ethmoid
sinuses

Zygoma

Greater wing of
sphenoid bone

Posterior
ethmoid
sinuses
Sphenoid
sinus

P

Dorsum sella of
sphenoid bone

FIG. 2.78 Axial CT of facial bones and ethmoid sinuses.

55

56

CHAPTER 2 Cranium and Facial Bones

Inferior Nasal Conchae

Vomer

The inferior nasal conchae (inferior nasal turbinates)
arise from the maxillary bones and project horizontally
into the nasal cavity (Figs. 2.67, 2.72, and 2.77). They
can be identified by their scroll-like appearance. These
conchae in conjunction with the superior and middle
nasal conchae of the ethmoid bone divide the nasal cavity
into three openings or meati, termed superior, middle,
and inferior (Figs. 2.72, 2.79, and 2.80).

The vomer is an unpaired facial bone located on the
midsagittal line. The vomer forms the inferior portion of
the bony nasal septum as it projects superiorly to articulate with the perpendicular plate of the ethmoid bone
(Figs. 2.8, 2.9, 2.67, and 2.72).

Superior nasal
concha
Superior nasal
meatus

Frontal sinus
Sphenoid sinus

Middle nasal
concha

Opening for
eustachian
tube

Middle nasal
meatus

Inferior nasal
concha

Inferior nasal
meatus

FIG. 2.79 Sagittal view of nasal meatus.
Anterior
ethmoid
air cell

Posterior
ethmoid
air cell

S

Sphenoethmoidal
recess

Sella turcica

Frontal sinus

Superior
nasal meatus

P
Sphenoid
sinus

A
Middle nasal
concha

Basal lamella
of middle
concha
(turbinate)
Nasopharynx
Middle nasal
meatus

Inferior
nasal
meatus

I

FIG. 2.80 Sagittal CT reformat of nasal meatus.

Inferior
nasal
concha

CHAPTER 2 Cranium and Facial Bones

vertical portion of the mandible is called the ramus
(Figs. 2.71 and 2.81–2.83). Each ramus has two processes at its superior portion: the coronoid process, anteriorly, and the condyloid process (condyle), posteriorly
(Figs. 2.81, 2.82, 2.84, and 2.85). They are separated by
a concave surface called the mandibular notch. The
coronoid process serves as an attachment site for the
temporalis and masseter muscles, whereas the condyloid
process articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint (TMJ)
(Figs. 2.82 and 2.86).

Mandible
The largest facial bone is the mandible. This bone is
composed primarily of horizontal and vertical portions
(Figs. 2.81 and 2.82). The angle created by the junction
of these two portions is termed the gonion. The curved
horizontal portion, called the body, contains an alveolar
process (similar to the maxilla) that receives the roots of
the teeth of the lower jaw. The mental foramina extend
through the body of the mandible and allow passage of
the mental artery and nerve (Figs. 2.81 and 2.82). The

Coronoid process

Neck
Condyloid
process

Alveolar portion
Mandibular
notch
Symphysis

Ramus

Mental
protuberance

Angle (gonion)

Mental foramen

Body

FIG. 2.81 Lateral view of mandible.

Zygomatic
arch
S

Mandibular
notch

Mandibular
fossa of
temporal
bone

Zygoma

External
auditory meatus

Coronoid
process of
mandible

Condyloid
process of
mandible
(condyle)
A

P

Alveolar
process of
mandible

Ramus
of mandible
Angle of
mandible
(gonion)

Mental foramen

57

I

Body of mandible

FIG. 2.82 3D CT of lateral aspect of mandible.

CHAPTER 2 Cranium and Facial Bones

58

Anterior clinoid
process

S

Greater wing
of sphenoid bone

Sphenoid
sinus

Pterygoid process
of sphenoid bone
(lateral plate)

Foramen
rotundum

I
Pterygoid hamulus
of sphenoid bone

Ramus of
mandible

Zygomatic
arch

FIG. 2.83 Coronal CT of mandibular rami.

A

Maxillary
sinus

Zygoma
Coronoid
process
of mandible

Mandibular
notch

Mandibular
ramus

Condyloid
process of
mandible
(condyle)
Occipital
condyle

Foramen
magnum
P

FIG. 2.84 Axial CT of mandibular rami.

CHAPTER 2 Cranium and Facial Bones

A
Zygoma

Zygomatic process
of temporal bone
Condyloid process
of mandible
(condyle)

Clivus
Hypoglossal
canal

Foramen
magnum
P

FIG. 2.85 Axial CT of mandibular condyles.

59

60

CHAPTER 2 Cranium and Facial Bones

TEMPOROMANDIBULAR JOINT
The TMJ is a modified hinge joint that allows for the
necessary motions of mastication.

condyloid process of the mandible (condyle). The articular eminence creates the anterior boundary of the joint,
preventing the forward displacement of the mandibular
condyle (Figs. 2.86 and 2.87).

Bony Anatomy
The mandibular fossa and articular eminence of the temporal bone form the superior articulating surface for the
Articular Articular disk Posterior
eminence (meniscus) band

Mandibular
fossa

Anterior
band

FIG. 2.86 Lateral view of temporomandibular joint.

Lateral pterygoid
muscle

Mandibular
fossa

Condyloid process
of mandible (condyle)

S

External
auditory
meatus

Articular
eminence
A

P

Condyloid process
of mandible (condyle)

I

Mastoid
air cells

FIG. 2.87 Sagittal CT reformat of temporomandibular joint.

CHAPTER 2 Cranium and Facial Bones

articular disk is not tightly bound to the fossa but
moves anteriorly with the condyle. Several ligaments
help maintain the position of the articular disk. The
articular disk is attached to the medial and lateral
surfaces of the condyle by the collateral ligaments
(Figs. 2.89 and 2.90). Lateral stability is provided by the
temporomandibular ligament (lateral ligament), which
extends from the articular eminence and zygomatic
process to the posterior aspect of the articular disk and
the condylar head and neck (Fig. 2.91). Additionally,
this ligament restricts the posterior movement of the
condyle and articular disk.

Articular Disk and Ligaments
The articular disk, frequently called the meniscus, is
shaped like a bowtie and is interposed between the mandibular condyle and fossa to act as a shock absorber
during jaw movement (Figs. 2.86, 2.88, and 2.89). The
anterior and posterior portions of the meniscus are referred to as the anterior and posterior bands, respectively. The anterior band attaches to the lateral pterygoid muscle, and the posterior band has fibrous
connections to both the temporal bone and the posterior aspect of the condyle (Figs. 2.86 and 2.88). The

S

Mandibular fossa

External auditory meatus

Articular eminence

Condyloid process

Articular disk

I
A, closed

S

Articular disk

Posterior band

Condyloid process

Anterior band

61

P

I
B, open

FIG. 2.88 Sagittal, T1-weighted MRI of temporomandibular joint and articular disk. (A) Closed. (B) Open.

62

CHAPTER 2 Cranium and Facial Bones
Articular
disk (meniscus)

Mandibular
fossa

Fibrous
capsule

Joint
capsule

Lateral
collateral
ligament
Medial
collateral
ligament

Condyloid
process

Joint
capsule

FIG. 2.89 Coronal view of temporomandibular joint and collateral ligaments.

S

Mandibular fossa
Articular disk
Condyloid process
Medial collateral ligament
Lateral collateral ligament

L

R

I

FIG. 2.90 Coronal, T1-weighted MRI of temporomandibular joint.

CHAPTER 2 Cranium and Facial Bones
Zygomatic
process

Fibrous
capsule

63

Temporal
bone

Styloid
process
Temporomandibular
(lateral) ligament

Stylomandibular
ligament

Angle of
mandible

FIG. 2.91 Sagittal view of temporomandibular joint and lateral ligament.

Muscles
The cooperative actions of four muscles located on each
side of the TMJ provide the movement of the mandible
and are collectively referred to as the muscles of mastication (Fig. 2.92). The fan-shaped temporalis muscle originates on the temporal fossa, inserts on the coronoid
process and anterior ramus of the mandible, and elevates
the mandible. The masseter muscle is the strongest
muscle of the jaw, arising from the zygomatic arch and

inserting on the ramus and angle of the mandible. Its
actions include elevation of the mandible (Figs. 2.92 and
2.93). The pterygoid muscles (medial and lateral) originate from the pterygoid processes of the sphenoid bone
and insert on the angle of the mandible and condylar
process, respectively. The medial pterygoid muscle acts
to close the jaw, whereas the lateral pterygoid muscle
opens the jaw and protrudes and moves the mandible
from side to side (Figs. 2.92, 2.94, and 2.95).

Temporalis
muscle

Lateral
pterygoid
muscle
Medial
pterygoid
muscle
Masseter
muscle
Angle of
mandible

FIG. 2.92 Muscles of mastication.

Condyloid
process of
mandible
Ramus of
mandible

64

CHAPTER 2 Cranium and Facial Bones

S

Temporalis
muscle
R

L

Masseter
muscle

Hard
palate

Buccinator
muscle

Tongue

I

FIG. 2.93 Coronal, T1-weighted MRI of muscles of mastication.

CHAPTER 2 Cranium and Facial Bones
Lateral pterygoid
muscle

Medial pterygoid
muscle
A

Masseter
muscle

R

L

Condyloid
process

P

FIG. 2.94 Axial, T1-weighted MRI of pterygoid muscles.

A

Pterygoid process
of sphenoid bone
Lateral
pterygoid
muscle

Masseter
muscle

Temporalis
muscle

L

R

Medial
pterygoid
muscle

P

FIG. 2.95 Axial CT of temporomandibular joint and muscles of mastication.

65

66

CHAPTER 2 Cranium and Facial Bones

PARANASAL SINUSES
The paranasal sinuses are air-containing cavities within
the facial bones and skull that communicate with the
nasal cavity. The nasal cavity is lined by nasal mucosa
and is responsible for filtering airborne particles as it

Sphenoid
sinuses

warms and humidifies air going into the lungs. The
sinuses are named after the bones in which they originate: ethmoid, maxillary, sphenoid, and frontal. There
is great variance in the size, shape, and development
of these sinuses within each individual (Figs. 2.96
and 2.97).

Frontal
sinuses

Ethmoid
sinuses

Maxillary
sinus

FIG. 2.96 Anterior view of paranasal sinuses.

Frontal
sinus

Posterior
ethmoid
sinus

Anterior
ethmoid
sinus
Maxillary
sinus

Sphenoid
sinus

FIG. 2.97 Lateral view of paranasal sinuses.

CHAPTER 2 Cranium and Facial Bones

Ethmoid
The ethmoid sinuses are contained within the lateral
masses (labyrinths) of the ethmoid bone and number in
the adult between 3 to 18 cells. They are present at birth
and continue to grow and honeycomb into a varying
number of air cells through puberty. The ethmoid sinuses

67

are divided into anterior and posterior groups by the
basal lamella of the middle conchae (turbinates). The
basal lamella is the lateral attachment of the middle nasal
conchae to the lamina papyracea (Figs. 2.80 and 2.98).
The anterior group drains into the middle nasal meatus,
and the posterior group drains into the superior nasal
meatus (Figs. 2.79, 2.80 and 2.96–2.100; Table 2.3).

A

Nasal bone

Lacrimal
bone
Ethmoid
bone

Anterior
ethmoid
air cell

Zygoma
Posterior
ethmoid
air cell

Lamina
papyracea

Inferior orbital
fissure

Sphenoid
sinus

P

FIG. 2.98 Axial CT of sphenoid and ethmoid sinuses.
Ethmoid
sinuses

S

Frontal
sinus
Sphenoethmoidal
recess

Pituitary
gland

Superior nasal
concha
Superior
nasal meatus

Sphenoid
sinus
A

P

Middle
nasal concha
Middle nasal
meatus

Inferior nasal
meatus

Inferior nasal
concha

I

FIG. 2.99 Sagittal, T1-weighted MRI of sphenoid sinus.

68

CHAPTER 2 Cranium and Facial Bones
S

Superior
nasal meatus
Ethmoid
sinus

Ethmoid
bulla

Middle
nasal meatus

Middle nasal
concha of
ethmoid bone

Maxillary
sinus

Inferior
nasal concha

I

FIG. 2.100 Coronal CT of ethmoid and maxillary sinuses.

TABLE 2.3

Paranasal Sinus Drainage Location

Sinus

Drainage Location

Ethmoid: anterior
Ethmoid: posterior
Maxillary
Sphenoid
Frontal

Middle nasal meatus
Superior nasal meatus
Middle nasal meatus
Sphenoethmoidal recess
Middle nasal meatus

Inferior nasal meatus

CHAPTER 2 Cranium and Facial Bones

Maxillary
The paired maxillary sinuses (antrum of Highmore)
are located within the body of the maxilla, below the
orbit and lateral to the nose. These triangular cavities
are the largest of the paranasal sinuses in adults but
are just small cavities at birth. Their growth stops at

Inferior
nasal concha

A

69

approximately the age of 15. The roots of the teeth
and the maxillary sinuses are separated by a very thin
layer of bone. Often it is difficult to differentiate between the symptoms of sinusitis and infection of the
teeth. The maxillary sinuses drain into the middle
nasal meatus (Figs. 2.96, 2.97, 2.100, and 2.101;
Table 2.3).

Nasolacrimal
duct

Maxilla

Zygoma

Maxillary sinus

Perpendicular portion
of palatine bone
Pterygomaxillary
fossa
Pterygomaxillary
fissure

Nasal
septum

Pterygoid
process

P

FIG. 2.101 Axial CT of maxillary sinuses.

70

CHAPTER 2 Cranium and Facial Bones

Sphenoid
The sphenoid sinuses are present at birth but contain red
marrow and are therefore devoid of air. Pneumatization
of the sphenoid sinuses may be seen as early as 2 years
of age. Major growth of the sinuses occurs in the third
to fifth year, and they typically assume adult configuration between 10 and 14 years of age.

Sphenoid sinuses are normally paired and occupy the
body of the sphenoid bone just below the sella turcica.
Each sphenoid sinus opens into the sphenoethmoidal
recess directly above the superior concha and drains into
the superior nasal meatus (Figs. 2.80, 2.96–2.99, 2.102,
and 2.103; Table 2.3).

S

Optic
chiasm

R

L

Pituitary
gland

Sphenoid
sinus
Internal
carotid
artery
I

FIG. 2.102 Coronal, T1-weighted MRI of sphenoid sinuses.
S

Optic
canal
Anterior
clinoid
process

Optic
strut
Sphenoid
sinus

Superior
orbital
fissure

Zygomatic
arch
Middle
nasal
concha

Foramen
rotundum

Inferior nasal
concha
Ramus of
mandible
Hard palate
I

FIG. 2.103 Coronal CT of sphenoid sinuses.

CHAPTER 2 Cranium and Facial Bones

Frontal
The frontal sinuses are located within the vertical portion
of the frontal bone (Figs. 2.96, 2.97, and 2.99). These
sinuses are typically paired and are separated along
the sagittal plane by a septum (Fig. 2.104). The frontal

sinuses are rarely symmetric, vary greatly in size, and can
contain numerous septa. These sinuses do not form or
become aerated in the frontal bone until approximately
age 6, making them the only paranasal sinuses that are
absent at birth. The frontal sinuses drain into the middle
nasal meatus (Figs. 2.99 and 2.100; Table 2.3).

Septum

S

Frontal
sinus
Nasal
bone

Perpendicular
plate of ethmoid
bone

I

71

Frontal process of maxilla

FIG. 2.104 Coronal CT of frontal sinuses.

CHAPTER 2 Cranium and Facial Bones

72

Osteomeatal Unit
Drainage of the paranasal sinuses occurs through various openings, or ostia. The major drainage pathways and
structures of these osteomeatal channels form the osteomeatal unit (OMU) (Figs. 2.105–2.107). There are two
osteomeatal channels: the anterior OMU and posterior
OMU. The anterior OMU includes the ostia for the
frontal and maxillary sinuses, frontal recess, infundibulum, and middle meatus. The anterior OMU provides
communication between the frontal, anterior ethmoid,

Ethmoid
sinus

and maxillary sinuses. The posterior OMU consists of
the sphenoethmoidal recess and the superior nasal meatus, which communicate with the posterior ethmoid air
cells. The sphenoethmoidal recess lies just lateral to the
nasal septum, above the superior nasal concha, and
drains the sphenoid sinuses. Key OMU structures to
identify include the infundibulum, middle meatus, uncinate process, semilunar hiatus, and ethmoid bulla.
The infundibulum is a narrow oblong canal that serves
as the primary drainage pathway from the maxillary
sinuses into the middle meatus. The medial wall of the

S
Ethmoid bulla
Infundibulum

Semilunar
hiatus

Uncinate
process of
ethmoid bone

Middle nasal
concha

Maxillary
sinus
L

R
I

Inferior nasal
concha

Middle nasal
meatus

FIG. 2.105 Coronal view of osteomeatal unit.

S
Crista
galli

Roof of
orbit

Orbital plate
of frontal bone

Medial wall
of orbit

Orbital plate
of ethmoid bone
(lamina papyracea)

Ethmoid bulla
Lateral wall
of orbit

Infundibulum

Semilunar
hiatus
Maxilla and
floor of orbit

Zygoma
L

R

Uncinate
process

Maxillary
sinus

Infraorbital
groove
Middle nasal
meatus
I

FIG. 2.106 Coronal CT of osteomeatal unit.

CHAPTER 2 Cranium and Facial Bones

Frontal recess

73

Ethmoid bulla

S

Semilunar
hiatus
Infundibulum

R

L

Maxillary sinus

Middle nasal
meatus

I

Uncinate
process

FIG. 2.107 Coronal CT of frontal recess.
infundibulum is created by the uncinate process. The
uncinate process is a thin, hook-shaped bony plate that
arises from the floor of the anterior ethmoid sinuses and
projects posteriorly and inferiorly, ending in a free edge.
The free edge of the uncinate process forms the semilunar
hiatus, which opens directly into the middle meatus. The
semilunar hiatus is a gap located between the ethmoid
bulla and uncinate process that forms the opening of the
infundibulum. Also draining into the middle meatus is
the ethmoid bulla, located superior and posterior to the
infundibulum, which receives drainage from the anterior
ethmoid air cells (Figs. 2.105–2.107).

ORBIT
Bony Orbit
The bony orbits are cone-shaped recesses that contain
the globes, extraocular muscles, blood vessels, nerves,
adipose and connective tissues, and most of the lacrimal
apparatus. The junction of the frontal, sphenoid, and
ethmoid bones of the cranium and the lacrimal, maxillary, palatine, and z