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1087

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Craniovertebral Correlation Mark

E. Schweitzer,1

Junction:

Jurg

Hodler,2

The anatomy of the craniovertebral may be well visualized by routine

Vinicio

‘

Normal

Cervilla,2

and

junction, although complex, MR imaging. This essay dis-

cusses the anatomy of the complex articulations of the craniovertebraljunction. Representative MR images and gross anatomic photographs are presented to illustrate the intricate ligamentous and articular anatomy. Knowledge of the normal anatomy of the

Anatomy

Donald

Resnick2

axial levels. After imaging, each specimen was frozen sectioned with a band saw at 4-mm intervals because

i mm of tissue

corresponding

specimen

MR-Anatomic

neoplasm. The resultant abnormal ics may lead to neurologic sequelae or pain.

External

abnormalities

Materials

Three discarded.

Methods

cadavers

disarticulation

were

of the

sectioned

upper

It was necessary

at the level of the pubis

extremities.

The

to obtain

lower

extremities

a large specimen

the amount of air in the spinal canal. Routine radiographs

was macerated

by the saw. The

section

and

with

anatomic

texts

[i

-3].

Correlation

mechan-

and

and

in each section

again and then approximately

resulting sections correlated closely in position and thickness with those of the MR images. The MR images were correlated with the

occipitoatlantoaxial region is necessary in order to understand the common disorders that affect this area. The most common disorders are trauma and arthropathies, but also include congenital

with MR

with were

to minimize

were used

Craniocervical

Ligaments

The

anterior

atlantooccipital

membrane

upper

aspect

of the anterior

arch of Cl

extends

from

the

to the foramen

magnum. It is visualized as an intermediate-signal structure with radiating fascicles just above and anteriorto the odontoid process. Although it radiates anatomically, its fascicles appear

nearly parallel on MR images (Figs. 1 -4). The signal intensity

of the anterior atlantoaxial membrane is greater than that of surveyed fluoroscopically, placed in a neutral position, and frozen. the other ligaments of the craniovertebral junction. Before MR imaging, the specimens were thawed and heated to 37#{176}C. The posterior atlantooccipital membrane is an analogous to exclude

significant

abnormalities.

The

cadaveric

necks

then

were

Each specimen was imaged with a i .5-T imager (Signa, General Electric Medical Systems, Milwaukee, WI) in the sagittal, coronal, and axial planes through the craniovertebral junction. Images were obtamed with a i 0-cm field of view, a 256 x 1 92 matrix, and two signal acquisitions. Spin-echo sequences, 3000/35 (TRITE), with a slice thickness of 4 mm and i -mm interslice gap were used. One specimen was precisely marked at the levels at which the sagittal images were obtained. This was repeated with a second specimen for the coronal levels and with a third specimen for the

structure

extending

from

the posterior

arch of Ci

to the

foramen magnum. It is thinner and looser than the anterior membrane. On MR images, it is moderate in thickness and of low signal with a somewhat wavy contour (Figs. 1 -4). It has

apertures

that allow passage

of the vertebral

arteries

(Fig. 3).

The atlantooccipital ligaments are seen just external to the capsule of the lateral atlantooccipital joints and are oriented vertically. These ligaments as well as the joint capsule are

Received September

1 3, 1991 : accepted after revision November 26, 1991. This work was supported in part by Veterans Affairs grant SA306. 1 Department of Radiology, Veterans Administration Medical Center, and University 2

Department

of California, San Diego, Medical Center, San Diego, CA 92161. of Radiology, Thomas Jefferson University Hospital, 132 S. 1 0th St., 1 096 Main Bldg., Philadelphia, PA 191 07. Address reprint requests to M. E.

Schweitzer. AJR 158:1087-1090,

May

1992 0361-803x/92/1

585-1087

© American

Roentgen

Ray Society

1088

SCHWEITZER

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Key to Abbreviations

Used

in Figures

ET AL.

AJR:158,

redundant and lax to allow rotatory motion at these articulations (Fig. 4). The anterior atlantoaxial ligament extends from the anterior midportion of the dens to the inferior aspect of the anterior arch of Cl . It consists of two distinctly visualized low-intensity

a

alar ligaments

b C

anterior anterior anterior

C

clivus

d

anterior longitudinal ligament dens (odontoid process)

on midline images (Fig. 1).

0

e

apical ligament

Internal

f

articular cartilage atlantooccipital ligaments transverse ligament of atlas inferior longitudinal fasciculus ligament

b’

g

h hi

atlantoaxial ligament (deep portion) atlantoaxial ligament (superficial portion) atlantooccipital membrane

(in fat)

hs

superior ligament

i k I m n

capsule of capsule of capsule of capsule of interspinous

0

occiput

p r

ligamenta posterior

flava atlantooccipital

5

posterior

longitudinal

t

tectorial vertebral

V

longitudinal

fasciculus

separated

by a high-signal-intensity

1 and 2). Interspinous ligaments and are seen as several separate

Craniocervical

is visualized

fat plane (Figs.

have an oblique orientation fibers of intermediate signal

Ligaments

as a very low signal band (Figs. 1 and 2).

The transverse ligament is a thick band with intermediate signal oriented in the coronal plane extending from a tubercle

of cruciform

on the inner aspect

joint

of one side of the atlas to a tubercle

the opposite side. Vertical inferiorly to the transverse

These

joint

superior

and inferior

extensions ligament

fasciculi

extend superiorly (Figs. 1 2, and ,

have lower

on and 4-6).

MR signal

than does the transverse ligament. The transverse ligament and its fasciculi have a cross shape and together constitute the cruciform ligament (Fig. 1). The apical ligament is not directly visible on MR or anatomic sections. It lies superior to the dens extending to the occipital bone and is surrounded by fat (Fig. 2). It lies between the superior longitudinal fasciculus of the cruciform ligament and the anterior atlantooccipital membrane. The alar ligaments are short and broad and of intermediate

membrane

ligament

membrane artery

atlas (Cl) axis (C2)

1

2

fascicles

The tectorial membrane is the superior extension of the posterior longitudinal ligament and attaches to the anterior lateral aspect of the foramen magnum. This strong ligament

of cruciform

anterior median atlantoaxial atlantooccipital joint lateral atlantoaxial joint posterior median atlantoaxial ligament

May 1992

signal (Figs. 1 and 2). They extend outward

4

from the superior

.,,‘.

Fig. 1.-A and B, Sagittal midline MR image (A) and specimen photograph (B) show transverse ligament (h) and its superior (hs) and inferior (hi) fascicles, which together form cruciform ligament. These ligaments anchor dens and prevent instability of anterior and posterior median atlantoaxial joints. Posterior to cruciform ligament lies posterior longitudinal ligament (5) continuing cranially as strong tectorial membrane (t). Anterior to C2 lies anterior longitudinal atlantoaxial

ligament ligament

(d).

Deep

to this ligament

is anterior

atiantoaxial

ligament,

which

attaches

anterior

arch

of Cl

to anterior

body

of C2. Anterior

consists of superficial (b’) and deep (b) fibers. Posteriorly, posterior atiantooccipital membrane (r) and interspinous ligaments (n) act to attach posterior aspect of foremen magnum and spinous processes of Cl and C2, preventing hyperflexion. Ligaments cranial to dens are complex and, with exceptions of tectorial membrane (t) and alar ligament (a), are weak. Alar ligaments extend outward from dens to lie anterior to apical ligament before attaching to occipital condyles. Anterior atiantooccipital membrane (c) is superior extension of anterior atlantoaxial ligament. This membrane

extends

from

anterior

arch

of Cl

to clivus

and is broad,

densely

woven

fibroelastic

band.

Ligamenta

flava

(p) are not prominent in cervical spine and are more anterior than inferior attachment of oblique course, becoming more posterior membrane (r).

not seen craniad to Cl. Below Cl, interspinous ligaments (n) have oblique orientation with cranial attachment each ligament. lnterspinous ligament between posterior arch of Cl (1) and occiput (0) has oppositely oriented at cranial attachment. These ligaments are continuous with and are posterior extension of posterior atlantoaxial

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Fig. 2.-A and B, Sagittal MR image at lateral aspect of dens (A) and corresponding specimen photograph (B) show posterior atlantooccipital membrane (r), which is cranial continuation of posterior atlantoaxial ligaments. Posterior atlantooccipital membrane (r) extends from upper aspect of posterior arch of Cl (1) to posterior aspect of foramen magnum (0). It is broader, thinner, and looser than analogous structure seen anteriorly, anterior atlantooccipital membrane (c). Anteriorly lies anterior longitudinal ligament (d), which extends length of spine and becomes fixed at front of body of axis (2) and at anterior arch of atlas (1). Anterior longitudinal ligament (d) is most anterior ligamentous structure and extends to skull base. Anterior atiantoaxial ligament (b) is inferior extension

of anterior

atiantooccipital

inferior aspect of anterior arch of Cl. superficial (b’), are separated by fat.

membrane

We noted

(c). Anterior

both on anatomic

atlantoaxial sections;

ligament

on MR images,

is a strong band extending from anterior midportion of dens to two distinct fascicles of this ligament, one deep (b) and one

Fig. 3.-A and B, sagittal MR images (A) and corresponding specimen photograph (B) show articular cartilage (f) at atlantooccipital joint. These are paired true synovial joints with prominent lax capsules (k). Anterior longitu-

dinal ligament atiantooccipital

(d) as well as anterior membrane (c) are seen on these sections since both are broad In coronal plane. Anterior atiantooccipital membrane (c) consists of densely woven fibroelastic fibers that radiate in

a lateral pattern rather than linear fascicles that make up anterior longitudinal ligament (d). Ligamenta flava (p) connecting lamina of adjacent verte-

brae may be seen adjacent atlantoaxial joint.

Fig. 4.-A

and B, Axial

to lateral

MR image

(A) and corresponding

specimen

photograph

(B) show

atlantooccipital

occipital

condyles (0) and lateral masses of Cl (1). Just medial to these joints lies anterior atlantooccipital

cartilage

(f) is shown.

joints

with articular

cartilage

(f) formed

by

membrane (c). Posterior to this and just anterior to tip of dens (D) lies apical ligament (e), not directly discernible within adjacent fat. Lateral to apical ligament is cranial insertion of capsular fibers of anterior median atiantoaxial joint (i). Cruciform ligament (h) interdigitating with fibers of accessory ligaments is seen. These ligaments extend from lateral masses of Cl and act to reinforce lateral atlantoaxial joints and alar ligaments. Upper aspect of posterior median atiantoaxial joint with its articulating continuation

of posterior

Posterior

to this joint and anterior

longitudinal

ligament.

to spinal

Atlantooccipital

cord lies posterior

ligaments

longitudinal

(g) act to reinforce

ligament

margins

(5).

Craniad

of capsule

to this level,

of atlantooccipital

tectorial

joints.

membrane

is

1090

SCHWEITZER

ET

AL.

AJR:158,

May 1992

Fig. 5.-A andB, Axial MR image (A) and corresponding specimen photograph

(B)

show

Caudal capsular

articulations of dens. insertion of atlantooc-

joints (k) can be seen on these images. Anterior longitudinal ligament (d) is becoming more cordlike at this level. Deep to anterior longitudinal hgament lies anterior atiantooccipital membrane (c).

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cipital

.-

;

ji

.i

.

:

#{149} .

Fig. 6.-A and B, Coronal MR image (A) and corresponding specimen photograph (B) show articular cartilage (f) at posterior median and lateral atlantoaxial joints forming articulations between atlas (1) and axis (2). Apical hgament at tip of dens lies within fat (e). Capsular fibers (I) of lateral atiantoaxial

joints are seen as well. Portion of cmciform ligament (h) is seen adjacent to dens. Tectorial membrane acts as primary reinforcer of upper cervical spine in flexion and extension.

and lateral aspect condyle.

of the dens to the medial

aspect

of the

occipital

intermediate

signal

intensity

usually

adjacent

to cortical

bone.

However, at the posterior median atlantoaxial joint, cartilage is seen on the anterior aspect of the transverse ligament.

Articulations Four joints are present between the occiput and Cl and C2: the atlantooccipital joints (Fig. 4), the anterior median atlantoaxial joint (Fig. 1), the posterior median atlantoaxial joint (Figs. 1 3, and 4), and the lateral atlantoaxialjoints (Figs. ,

3 and 6). The first and last of these are paired. All four articulations are true synovial joints with hyaline articular cartilage and prominent lax capsules. The cartilage is seen as

REFERENCES 1 . Netter RH. The CIBA collection of medical illustrations, vol. 8, musculoskeletal system, part 1 . Anatomy, physiology and metabollc disorders. Summit, NJ: CIBA-Geigy, 1987 2. VanGilden SC, Menezes AA, Dolon KD. The craniovertebraijunction and its abnormalities. Mount Kisco, NY: Futura, 1987:14-27 3. Williams PL, Warwick R, Dyston M, Banister LH. Gray’s anatomy, 37th ed. Edinburgh: Churchill-Livingstone, 1989