Prebasioccipital arch - a rare type of occipital vertebra
Pain during full range of neck movements
CT base of skull
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Noncontrast highresolution CT reveals hypoplasia of basiocciput with prebasioccipital arch with basilar invagination and a possibility of neural dysgenesis ( Chiari malformation).
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The study reveals a hypoplastic clivus suggesting basioccipital hypoplasia. There is basilar invagination as evidenced by tip of dens and anterior arch of atlas lying approximately 19 mm above the Chamberlains line. Weckenheims clivus baseline is normal and Welchers basal angle is 135 degrees.
A bony arch is noted at the tip of clivus which is continuous laterally with occipital condyles consistent with the rare occurence of prebasioccipital arch. The bilateral atlantooccipital and atlantoaxial joints are normal.
There also is a hypodense fluid attenuation central area in the cervical canal on soft tissue windows caudal to C3 level may represent syringomyelia. (MRI was recommended )
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