CT and MR Imaging of the Central Skull Base Part

Techniques,

1:

Embryologic

Development,

and

Anatomy1

Fredj Lame, MD Lyn Nadel, MD Ira F. Braun, MD2

Recent

advances

proach

in surgical

previously

The

radiologist

and

the

inoperable requires

pathologic

imaging

deep-seated of this

in order

velopment

my as seen

on computed

tomographic

surgeons of the

of the

region

and the

to ap-

skull

base.

normal

anatomy

an understanding

of

extent

of pathologic

approach. The embryologic normal gross anatomy, and

and magnetic

deanato-

resonance

images

presented.

. INTRODUCTION Recent advances in microsurgical technique operating microscope have now enabled ble deep-seated lesions of the skull base. of such lesions is mandatory in planning complex region. It is therefore necessary knowledge of the anatomy of this region

and the more widespread use of the surgeons to approach previously inoperaPreoperative determination of the extent a surgical approach to this anatomically that the radiologist have a thorough as well as an understanding of which im-

aging method is best suited for the evaluation ing these regions. In this article, we describe magnetic resonance (MR) imaging techniques; gross, fossa.

of various disease processes affectcomputed tomographic (CT) and embryologic development; and

CT, and MR anatomy of the central skull base and floor of the middle cranial In Part 2 we will discuss various congenital and acquired lesions, both be,

nign and malignant, evaluation of central

affecting this region skull base lesions.

and suggest

imaging

strategies

for the

CT TECHNIQUE

The ness

skull base is best evaluated in the axial and of 1 .5-3 mm is used. For bone detail only,

Abbreviation: Index

DTPA

terms:

Skull,

RadloGraphics I

lesions

to determine

the surgical skull base,

.

enabled

knowledge

and help plan of the central

are

have

a thorough

spectrum

modalities

conditions

techniques

From

the

Richmond,

RSNA, Part

anatomy

1990; Department 2 1 and address:

#{149} Skull,

10:59

CT,

A section thickbone algorithm

acid

12.t21

1

#{149} Skull,

growth

and

development

#{149} Skull,

MR studies,

12.0

214

1-602

ofRadiology,

VA 23298-0615.

ed March 2 Current

dicthylenetriaminepcntaacetic

coronal planes. a high-resolution

Division

From

the

1989

received April 9; accepted Department of Radiology.

ofNeuroradiology, RSNA

scientific

Medical assembly.

April 16. Address Baptist Hospital

reprint of Miami.

College

Received requests

ofVirginia, February

Box 15,

1990;

615,

MCV

revision

Station, request.

to FJ.L.

1990 2 ofthis

article

will

appear

in the

September

1990

issue.

591

is employed

with

a wide

window

setting

(4 ,000 HU) If soft-tissue contrast in addition to bone information,

is needed contrast ma-

.

terial

administered

used.

The

intravenously

axial

study

should

is performed

be

in the

plane of the Reid baseline, drawn from the orbitomeatal

parallel line.

to a line Scans are

obtained

from

magnum

to the

suprasellar obtained

cistern. Direct coronal images are perpendicular to the Reid baseline.

the

foramen

If dental amalgam causes significant in the direct coronal plane or if the

cannot

tolerate

constructed overlapping,

.

the coronal

head

position,

re-

images can be obtained from thin (1 .5-2.0-mm) axial scans.

MR IMAGING

The skull head coil.

imaging

TECHNIQUE

base is imaged with Routine examination

in the midsagittal,

planes.

artifact patient

Ti-weighted

thickness image is first

as a scout

superior

and

midline.

Little

view.

inferior

and coronal

are obtained

times of 600-i of i 7-20 msec

definition. A section used. A midsagittal

standard consists of

axial,

images

with repetition and echo times

and serves

the

,000 msec for anatomic of 3-5 mm is obtained

It also shows

extent

of disease

use is made

the at the

of parasagittal

sections because of the confusing aspects of anatomy. Axial images are obtained from the suprasellar cistern to the nasopharynx. The axial study is usually repeated after the intra-

venous

administration

of gadolinium

enetriaminepentaacetic

acid

diethyl-

(DTPA)

(0.1

mmol/kg) Coronal images are then obtained from the anterior aspect of the sphenoid si.

nus

to the

foramen

T2-weighted

magnum.

the

shorter

Ti

enhancement. warranted, msec (second

value

soft-tissue in most

contrast obcases, with

and

Gd-DTPA

sequences

If a T2-weighted a repetition time

is employed

of 20-45

are of lesser

the skull base because (a) they time to the total examination

and (b) the additional tamed can be achieved,

msec

with

(first

with

sequence of 2,000-3,000

a double-echo

echo)

is

time

and 90 msec

(NH)

.

Chondrocranial

. EMBRYOLOGIC DEVELOPMENT The bones of the skull base are derived

from

cartilaginous

chon-

known

as the

drocranium, while the calvarial bones form from membranous bone (Fig i) The development of the cartilaginous skull base begins .

components

include

the alisphenoid (as), basioccipital (bo), exoccipital (eo) nasal capsule (nc) orbitosphenoid (Os), presphenoid (prs), postsphenoid (pts), and supraoccipital (so) The primordial foramina indude the foramen ovale (fo) foramen rotundum (I r) optic canal (oc) and superior orbital fissure (sof). ,

,

.

,

,

around the 40th day of gestation, with the conversion of mesenchyme into cartilage. This

mesenchyme

notochord brain

surrounds

to form

a floor

the

developing

for the base

of the

(2).

During the 5th week, the notochord becomes enclosed by the bodies of the upper cervical

echo).

precursors,

bone

,

sequences

in examining add significant

Figure 1. Drawing of the embryologic endocranial aspect of the skull base. (Redrawn from reference 3, p 1 1 5.) The membranous bone components include the frontal bone (FH) and nasal

vertebrae

and

passes

into

the

basioc-

ciput. Here it lies directly in contact with the endoderm of the embryonic pharynx. The notochord terminates in the body of the sphenoid,

just

caudad

to the

pituitary

fossa

at

the dural margin (Fig 2) Up to i 5 separate endochondral and intramembranous ossifica.

tion centers constitute the sphenoid bone (2) The greater wing of the sphenoid bone and the lateral pterygoid plate are derived from intramembranous ossification, while .

the medial

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in the region

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2. 3. Figures 2, 3. (2) Drawing of the midsagittal section depicting the course of the notochord. EP embryonic nasopharynx, fit floor of sella turcica, N = notochord, N = notochordal termination, OP = odontoid process of C-2, sop sphenooccipital plate. (3) Drawing of the midsagittal section of the skull base in a newborn. bo basioccipital bone, bs basisphenoid bone, eo = exoccipital bone, is = intersphenoid synchondrosis, sos = sphenooccipital synchondrosis. =

men The

rotundum, lesser wing

the greater nor

originates from (orbitosphenoid)

wing

(alisphenoid)

(presphenoid)

sphenoid)

and

the

cartilage.

portion

,

and posterior

of

the ante(post-

,

of the body

of the sphenoid bone are formed from cartilage (2) The basisphenoid part (Fig 3), the central cartilagiparts

.

nous bone,

precursor is formed

of the body from fusion

al hypophyseal cartilages rounding the developing rostrad

of the sphenoid of the two later-

containing pituitary

and surgland. Just

to this,

two cartilages fuse to form the presphenoid part (Fig 1), which develops into the anterior part of the sphenoid bone (2) At the same time, laterally, there fusion of the precursors of the lesser (orbi.

tosphenoid)

and the greater

(alisphenoid)

wings

sphenoid

The

of the

noid part, continuous, bone

anterior

to the

part,

greater

the sella sphenoid

wings

tuberculum,

which and

while

pterygoid

,

plates,

track (of the gives rise to the

of the pituitary postsphenoid

gland, is obliterated ossification centers.

skulls,

July

1990

.

postsphenoid

before

(Fig

for the orbital

plates

last one to the growth period. In base, cx-

of the frontal

bones and the most lateral parts of the greater wing of the sphenoid bone, is preformed in cartilage, while the remainder of the cranial vault undergoes membranous ossification (i,p us). Portions of the chondrocranium (unossifled cartilage) persist at birth, including the sphenooccipital junction, the sphenopetrous junction, and the foramen lacerum at the petrous apex (1 p i i 5) At birth, the sphenoid ,

phalobe

tenor

is composed

.

consisting of the body and lesser wings, and two lateral, each made up of a greater wing and pterygoid process. Subsequently in the first postnatal year, the greater wings and the body fuse around the pterygoid canal, while the lesser wings fuse medially above the an-

tumors (2) The inbetween the presparts

cept

sphenooc-

forms

by the In 0.4% of

.

separation at synchondroses. The cipital synchondrosis (Fig 3), the fuse, is primarily responsible for of the skull base in the postnatal summary, the entirety of the skull

bone

a persistent craniopharynit forms the basis of con-

geal canal exists; genital craniopharyngeal tersphenoid synchondrosis phenoid and fuses shortly

The Rathke anterior

expanding brain. Appositional growth takes place through addition to sutural edges and

with

and basi; 2)

ryngohypophyseal pouch) which ,

the

is associated

turcica, dorsum sellae, part (i pp 288-29 i

postnatal

presphe-

with which the lesser wings are forms the body of the sphenoid

postsphenoid the

bone.

is

The skull base expands through growth of endochondral remnants and because of forces applied to the growing sutures by the

of three

part of the body

parts:

and form

one central,

an elevated

smooth surface, the planum sphenoidale. The sphenoid and occipital bones are cornpletely fused by the 25th year (i pp 288,

291).

3)

birth.

Lame

et al

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.

,.

a

..

b.

Figure 4. Drawings of the exocranial (a) and endocranial (b) views of the skull base and of the coronal view of the sphenoid bone (c). ac antenor clinoid, C = clivus, cc carotid canal, cbs chiasmatic sulcus, cp cribriform plate, D dorsum sellae, fo foramen ovale, fr foramen rotundum,fs = foramen spinosum,fst floor of sella turcica, gs = greater sphenoid wing, ltc intratemporal crest,ff jugular foramen,jt jugular tubercle, LP = lateral pterygoid plate, is = lesser sphenoid wing, MP = medial pterygoid plate, oc = optic canal, OS orbital surface, p pterygoid fossa, P = pterygoid process, pc postenor clinoid, pof petrooccipital fissure, ps planum sphenoidale, ser opening into sphenoethmoid recess, sof superior orbital fissure, sps = sphenopetrosal synchondrosis, T tuberculum sellae, TS = temporal surface, vc = Vidian (pterygoid) canal.

I

s1f

o

C-

bone

and its foramina are involved in primary pathologic processes of bone, extracranial disease that extends intracranially, and intracranial

U

ANATOMY

.

The

Bone

the floor

of the middle

fossa; and contains the pituitary the sella turcica, as well as the ernous sinuses. This strategically

shape

that extends of the

that of a bird with

The sphenoid bone is the foundation of the central skull base. This anatomically complex structure contains vital foramina, which transmit important neurovascular structures;

constitutes

disease

base. The

Sphenold

cranial

gland within parasellar caylocated

:

ser

through

sphenoid

wings

the skull

bone

resembles

outstretched.

of a central

body;

two

sets course

It con-

the greater and lesser, which and two pterygoid processes, which are directed inferiorly (Fig 4). The sphenoid body is somewhat cubical. The superior surface articulates anteriorly sists

of wings, laterally;

with the cribriform plate of the ethmoid bone and contains a smooth central surface, the planum sphenoidale (Fig 4b) Posterior.

ly, the pression

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chiasmatic and leads

sulcus forms a slight laterally to the optic

Volume

10

deca-

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Figure through anterior oid, C

5.

within

the body,

High-resolution

coronal

CT scans

the skull base. Sections are arranged from (a) to posterior (e). ac anterior din= clivus, ca2 petrous portion of carotid artery, D = dorsum sellae, fo foramen ovale, fr = foramen rotundum, fs foramen spinosum, fst = floor of sella turcica, lof inferior orbital fissure, LP = lateral pterygoid plate, MP medial pterygoid plate, tip = nasopharynx, oc = optic canal, P = pterygoid process, p pterygoid fossa, pof petrooccipital fissure, S sphenoid sinus, sof superior orbital fissure, T tuberculum setlae, vc = Vidian canal.

e.

nals.

The

tion,

is found

tuberculum

sellae,

a bony

just posterior

eleva-

to this sulcus.

air cells

divided

by a septum,

into

which

two separate is usually some-

just posterior to 4b, Sc) The middle clinoid processes, two small cminences, form the anterolateral boundary of the sella turcica, while the dorsum sellae

what deflected, thereby rendering the mdividual cells asymmetric (Figs 5a, Sb, 6d). The cells may extend laterally into the great-

forms its posterior extent (i pp 288-29 i). The dorsum sellae terminates laterally into the posterior clinoid processes, which provide attachment for the tentorium. The body

with the nasal fossa the sphenoethmoid

merges medial

(Fig 4b) and form the middle cranial

The sella turcica the tuberculum

is situated sellae (Figs

.

,

laterally pterygoid

Anteriorly,

with bone.

July

the

with the greater wings plates (1 pp 288-291). sphenoid

the perpendicular The

1990

sphenoid

and

,

body

plate sinuses

er wing and into plates. Anteriorly,

the base of the pterygoid each cell communicates

through recess.

an opening

The greater wings course upward erally from both sides of the sphenoid

and

a portion of the floor fossa. Three important

into latbody

of fo-

articulates

of the ethmoid are contained

Lame

et al

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Figure 6. High-resolution axial CT scans of the skull base in an adult. Sections are arranged from caudal (a) to rostral (d). ac = anterior clinoid, c = clivus, ca3 = precavernous portion of carotid artery, cg = cristi galli, cs = cavernous sinus, D = dorsum sellae, fo = foramen ovate, fr = foramen rotundum, fs = foramen spinosum, lof inferior orbital fissure, OC optic canal, f= pterygopalatine fossa, S = sphenoid sinus, sof superior orbital fissure, sps sphenopetrosal synchondrosis, VC = Vidian canal.

ramina

are found

the rotundum,

within

ovale,

the

and

greater

spinosum

wing:

fissure.

situated

border

from anteromedially to posterolaterally 4b, 6a, 6b, 7a) A ridge, the infratemporal

(Figs

crest, is found on the lateral surface of the greater wing and separates it into a superior temporal surface, which provides attachment for the temporalis muscle, and into an inferior

infratemporal

of the lateral nates (3) (Fig 4c). The orbital surface

surface,

pterygoid

from

plate

which

a

origi-

contains

the

wing

#{149} Lame

et al

lower

base of Laterally, this irregular margin articulates with the petrous portion of the temporal bone through the sphenopetrosal synchondrosis (Fig 4b) (1, pp 288-291).

The

lesser

pterygoid

plates

wings

bones that project anterior sphenoid

#{149}RadioGraphics

the

.

forms the posterolateral wall of the orbit and articulates with the orbital plates of the frontal and zygomatic bones. Its inferior margin forms the upper border of the inferior orbital

596

forms

5a) These portions of the greater wing also form the posterior boundary of the pterygopalatine fossa. The medial half of the greater wing forms the anterior edge of the foramen lacerum and

the pterygoid of the greater

margin

.

.

portion

Its superior

of the superior orbital fissure (Figs 4c, 5a) The foramen rotundum is located below the superior orbital fissure (Figs 4c,

canal

(Figs

in the

Sb, 7a)

are paired

triangular

laterally from body and end

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a.

b.

Figure

7. Axial CT scans of the skull base in a 2-year-old child. bo basiocciput, bs basisphenoid, Ca2 petrous portion of carotid artery, fo foramen ovate, fs foramen spinosum, pf= pterygopalatine fossa, pof petrooccipital fissure, sos = sphenooccipital synchondrosis, sps = sphenopetrosal synchondrosis, VC = Vidian canal.

points. They nor surface,

are composed of a smooth which is situated beneath

supea

small portion of frontal lobe, and an inferior surface, which forms the posterior roof of the orbit and the upper border of the superior orbital fissure (Fig 4c). Medially, the postenor border ends in the anterior clinoid

processes,

which

form

the anterior

ment of the tentorium (Figs 4b, optic canal traverses the medial of the lesser wing to the sphenoid pp

attach5c, 6d) The attachment body (i, .

288-291).

The pterygoid processes descend mnferiorly from the sphenoid body, one on each side, and are composed of a pair of plates, lateral and medial, the upper parts ofwhich are fused anteriorly (Figs 4a, 4c, Sb, Sc) The .

pterygoid fossa, from which arises the medial pterygoid and the tensor veli palatini musdes, 15 formed as the plates diverge posteriorly (Figs 4a, 5a, 6a, 8b) The anterior surface of the pterygoid process forms the pos-

The

lateral

pterygoid

of the

medial

wall

and provides

plate

of the

attachment

forms

a portion

infratemporal

fossa

for the lateral

ptery-

goid muscle. The medial surface of the lateral plate forms the lateral wall of the pterygoid fossa, providing attachment for the me-

dial The

pterygoid superior

forms the maxillary

The

muscle (3) (Figs 4a, 8a, 9a). aspect of its anterior border

posterior fissure.

medial

boundary

pterygoid

plate

feriorly as a hooklike hamulus, around which tensor yeli palatini is surface of the medial wall of the pterygoid

The

pharyngobasilar

posterior

more strictor

takes

process, the slung plate fossa

fascia

margin

inferiorly

of the

of the (1,

terminates the tendon

(3) forms (Figs

.

The

lateral

the medial 4a, 8a, 9). plate,

pharyngeal

pp

in-

pterygoid of the

is attached

medial

the superior origin

pterygo-

to the and

con-

288-291).

.

tenor

July

boundary

1990

of the pterygoid

fossa.

Lame

et al

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Figure

8.

clivus,

Ca4

Axial Ti -weighted MR images of the skull base, arranged from caudal (a) to rostral (d). C = cavernous portion of carotid artery, iac internal auditory canal, iof= inferior orbital fissure, LM lateral pterygoid muscle, LP lateral pterygoid plate, M Meckel cave, MM = medial pterygoid muscle, MP = medial pterygoid plate, np = nasopharynx, P = pterygoid process, p = pterygoid fossa, pg = pituitary gland, 5 sphenoid sinus, sof superior orbital fissure.

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C-

Figure 9. Coronal Ti -weighted MR images of the skull C = clivus, Cal cervical portion of carotid artery, Ca2 ous portion of carotid artery, Ca5 supraclinoid portion = lateral dural reflection of cavernous sinus, LM lateral MM medial pterygoid muscle, MP medial pterygoid = optic nerve, pg = pituitary gland, pof= petrooccipital branch of trigeminal nerve in foramen ovale, V trigeminal

July

1990

base

arranged

from

anterior

(a)

to posterior

(d).

of carotid artery, Ca4 = cavernof carotid artery, I = pituitary infundibulum, id pterygoid muscle, LP lateral pterygoid plate, plate, tip nasopharynx, oth optic chiasm, on fissure, S sphenoid sinus, V3 = mandibular nerve. petrous

portion

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.

Basal

OrbitalFissure.-The

superior

orbital

by the body lesser wing,

and

fissure

is bounded

triangular medially

of the sphenoid, above by the and below by the greater wing

is completed

bone verge

branch of the mandibular ramen is best visualized Se, 6a).

Foramina

Superior

laterally

as the greater (Figs 4c, 5a,

and 6c)

.

Foramen

by the frontal

of the

not,

lesser wings conThrough it course

meningeal

branches

of the

andophthalmicvemns

lacrimal

artery,

(1, pp 288-291).

foramen rotunis actually a canal in the base of sphenoid wing, is situated just in-

Foramen

Rotundum-The

dum, which the greater

ferior and lateral to the superior orbital fissure (Fig 4b, 4c) The canal extends obliquely forward and slightly mnferiorly, connecting

.

exocranial

Lacerum.-The foramen

lacerum

in reality,

medial

(Fig

a foramen,

brocartilage.

the oculomotor, trochlear, and abducens nerves; the first division of the trigeminal nerve, the orbital branch of the middle meningeal artery, various sympathetic filaments of the internal carotid plexus, the recurrent

nerve (4) This fowith axial CT (Figs

It is located

pterygoid

plate.

4a),

aspect

which

is

is covered

with

at the

of the

The

base

carotid

fi-

artery

is

not transmitted through the canal but rests on the endocranial aspect of the fibrocartilage that forms its floor (5) An inconstant .

meningeal

branch

of the ascending

pharyn-

geal artery and the nerve of the pterygoid canal actually pierce the cartilage and are therefore the only structures contained in the foramen (4) The foramen lacerum and carotid canal may be visualized on both axial .

and coronal 8c, 9b).

CT or MR images

(Figs

Se, 6a,

.

the middle tine fossa. nerve

( V2)

dum,

and

24 1)

.

means

Pterygoid (Vidian) CanaL-The canal is situated in the base of the pterygoid plates below the foramen rotundum in the sphenoid body (Fig 4c). It connects the pterygopalatine fossa anteriorly to the foramen Iacerum posteriorly and transmits the Vidian artery and nerve (4 ; 5 pp 23 5-24 1) The nerve of the pterygoid canal, the Vidian

cranial fossa to the pterygopalaThe canal transmits the maxillary ,

the

artery

emissary

of the

veins

foramen

rotun-

(4; 5, pp 235-

This foramen is best visualized of coronal CT (Fig 5a, Sb).

by

,

Foramen Ovale.-This foramen, situated in the medial aspect of the body of the sphenoid, transmits the mandibular nerve ( V3), emissary veins, and the accessory meningeal artery from the middle cranial fossa to the in-

nerve, is the continuation of the greater superficial petrosal nerve (from cranial nerve VII) after its union with the deep petrosal nerve. The Vidian artery, a branch of the terminal portion of the internal maxillary ar-

fratemporal fossa. Endocranially (Figs 4b, 6a) the foramen ovale is situated posterolateral to the posterior aspect of foramen rotundum; exocranially (Fig 4a) it is found at the

tery,

base of the mal size of (4) It can coronal CT

lateral pterygoid plate. The northis foramen varies considerably be visualized on both axial and scans, while soft-tissue lesions

provides internal

traversing ages (Figs

it are best seen Sd, 6a, 9c).

,

,

.

Foramen sum

is found

on coronal

on

the

foramen posteromedial

.

arises

in the pterygopalatmne

passes through or to the Vidian ity

to the

foramen

vessel

often

to the

et al

lacerum,

this

.

on axial 6a, 7a).

and

coronal

is best

CT scans

spinoaspect

of

just posterolaterthe endocranial skull base and latexocranially (Fig pass the middle and the recurrent

Pituitary

Anatomy

The pituitary gland (Fig 1 0) lies in the hypophyseal fossa and is covered by a circular fold of dura, the diaphragma sellae. The cayernous sinus borders the gland on each side (Fig 1 1). The gland is divided into two main

regions

on the basis

ic, morphologic,

of different

embryolog-

functional

characteris-

and

tics: the anterior cludes the pars

adenohypophysis, anterior and pars

separated

by the

posterior

neurohypophysis,

median

lobe (1, pp

#{149} Lame

and

MR im-

the

#{149} RadioGrapbics

fossa

the foramen lacerum posterinerve. Because of its proxim-

important collateral supply carotid artery (6) This canal

visualized (Figs Sb, S

Spinosum.-The

the greater sphenoid wing, al to the foramen ovale on (Figs 4b, 6a) aspect of the eral to the eustacian tube 4a) Through this foramen meningeal artery and vein

600

.

hypophyseal

eminence

which intermedia

cleft,

which and

the

main

and

inthe

includes posterior

1367-1368).

Volume

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4

a.

b. Figures 10, 11. (10) Midline sagittal Ti -weighted MR images of the skull base in an adult (a) and a child (b). bo basiocciput, bs basisphenoid, C = clivus, D dorsum sellae, pg = pituitary gland, S = sphenoid sinus, sos sphenooccipital synchondrosis. (11) Drawing of the coronal view of the region of the cavernous sinus Ca4 = cayernous portion of carotid artery; id lateral dural reflection; pg = pituitary gland; 5 sphenoid sinus; III, Ji’ V1, V2, and VI third, fourth, first di.

vision

sixth

of the

cranial

fifth,

nerves,

second

division

of the

fifth,

and

respectively.

es are medial to the cavernous sinuses. The Meckel cave, enclosing the trigemmnal ganglion, is situated at the posteroinferior aspect of the sinus (7) The uncus of the temporal lobe is related to the lateral wall as well. The cavernous sinus can be evaluated with coronal or axial CT or MR images (Figs 6c, 8c, 8d, 9b, 9c). .

C.

.

Cavernous

Sinus

Anatomy

The cavernous sinuses (Fig 1 1) are situated on each side of the body of the sphenoid bone and extend from the superior orbital fissure anteriorly to the petrous apex posteriorly. The internal carotid artery, surrounded by a sympathetic plexus, courses through the sinus, while the abducens nerve (cranial nerve VI) lies inferolateral to the artery. Proceeding from superior to inferior, the oculo-

motor

and

trochlear

nerves

and

the ophthal-

mic ( V1) and maxillary ( V2) divisions of the trigeminal nerve are each contained within separate fibrous sheaths within the lateral wall of the sinus (1 pp 695-696; 7) Endo,

thelium venous 695-696)

July

separates blood .

1990

these

contained The pituitary

. The

Clivus

clivus

Anatomy is that part

of the skull base situated between the foramen magnum and the dorsum sellae. Most consider it to include the basioccipital bone and the sphenoid body (8). The petrooccipital fissure forms the anterior lateral margin of the clivus, while the synchondrosis between the basioccipital and exoccipital bones forms the posterior lateral margins (5, p 243). The antenor margin of the clivus blends into the sphenoid sinus, while it slopes gently posteroinferiorly to form the anterior aspect of

.

structures

from

in the sinus and sphenoid

(1

the pp sinus-

,

Lame

et al

U

RadioGraphics

#{149} 601

the foramen magnum (Fig 4a, 4b). Inferiorly, the clivus is bounded by the nasopharynx (Figs Se, 6a, 7a, lOa).

.

ACknowledgments: The authors thank Nicholas E. Mackovak and Phillip Mattis for their artwork.

4

.

5

.

6.

7.

#{149}RadioGraphics

Gray H; Warwick R, Williams PL, eds. anatomy. 35th British ed. Philadelphia: Saunders, 1973. Sperber GH. Craniofacial embryology. ton: Wright, 1981; 87-101.

#{149} Lame

et al

Gray’s

Lockhart 1W, Hamilton GF, Fyfe 1W. Anatomy of the human body. Philadelphia: Lippincott, 1972; 40-42. Sondheimer FK. Basal foramina and canals. In: Newton Th, Potts DG, eds. Radiology of the skull and brain. New York: Mosby, 1971; 287-347. Meschan I An atlas of anatomy basic to radiology. Philadelphia: Saunders, 1975. Djindjian R, MerlandJj. Super-selective arteriography of the external carotid artery. Bertin: Springer-Verlag, 1978; 24-25. Daniels DL, Peck P, Mark L, Pojunas K, Wil.

hams AL, Haughton VM. imaging ofthe cavernous

REFERENCES .

2.

602

.

SUMMARY

The central skull base is a highly complex region. Knowledge of the normal development and anatomic relationships will lead to more accurate diagnoses. Examples of pathologic processes will be presented in Part 2.

U 1

3

8.

Magnetic resonance sinus. AJR 1985;

144: 1009-1014. Coin CG, Malakasian DR. Clivus. In: Newton Th, Potts DG, eds. Radiology of the skull and brain. New York: Mosby, 1 97 1 ; 348-3 56.

Bos-

Volume

10

Number

4