Developmental and Hereditary Disorders

Question 1

Items 290–292
290. In this tomogram of the base of the skull, the first cervical vertebra is

a. Unremarkable
b. Fused to the base of the skull
c. Completely absent
d. Displaced dorsally
e. Incorporated into the odontoid process (od)

Answer 1

290. The answer is b. (Osborn, pp 815–816.) In the tomogram, the first
     cervical vertebra, or atlas, is incompletely formed. The most ventral elements
     are apparent to the left of the left-pointing arrowhead, but the cortical
     bone of these elements is continuous with that of the skull. The
     elements of C1 that have formed have simply fused to the base of the
     skull. This assimilation of the atlas to the base of the skull is a congenital
     abnormality. It is often associated with a Chiari malformation of the hindbrain.

Question 2

291. The second cervical vertebra extends above the level of the foramen
     magnum and places the patient at high risk of having
     a. A meningoencephalocele
     b. A myelomeningocele
     c. Syringobulbia
     d. Syringomyelia
     e. Brainstem compression

Answer 2

291. The answer is e. (Osborn, pp 815–816.) This abnormally situated
     axis (C2) qualifies as basilar invagination of the skull. If the medulla oblongata
     is situated at a normal level, it is at risk of compression, but posterior
     fossa contents may be so caudally displaced that pontine structures are also
     at risk of compression. Hydrocephalus may develop with this degree of
     basilar invagination by virtue of obstruction of the flow of CSF through the
     foramen magnum. Syringomyelia or syringobulbia are occasionally associated
     with this anatomic variant, but they probably develop as a consequence
     of cervical cord or brainstem damage.

Question 3

292. In view of the unusually wide separation (double-barbed arrow) of
     caudal elements of the atlas from the odontoid process, one should suspect
     a. Instability of the atlantoaxial joint
     b. Hemorrhage into the atlantoaxial joint
     c. Fusion of C2 to C3
     d. Fracture of the odontoid process
     e. Fracture of the C2 spinous process

Answer 3

293. The answer is e. (Greenberg, 2/e, p 601.) All of these disturbances
     will produce intracranial calcifications in some cases. The calcifications in
     Sturge-Weber syndrome follow the gyral pattern of the cerebral cortex and
     consequently produce the railroad track pattern that is evident on plain
     x-ray of the skull. Calcium is deposited in the brain of the patient with
     Sturge-Weber syndrome, presumably because the abnormal vessels overlying
     the brain allow calcium, as well as iron, across the defective bloodbrain
     barrier. Craniopharyngioma and acoustic schwannoma produce
     calcifications, but these are obviously outside the cerebral cortex.