[Dermoid cyst in the fourth ventricle associated with Klippel-Feil syndrome].

Dermoid cysts in the central nervous system are often associated with various congenital disorders, especially dermal sinus and spina bifida. We report a case of dermoid cyst in the fourth ventricle associated with Klippel-Feil syndrome. A 47-year-old man with a long history of headache had been known to have a cystic lesion in the posterior fossa for 12 years. When he was referred to our hospital with complaints of transient tetraparesis, he showed bilateral cerebellar ataxia and minimal left hemiparesis. Furthermore, he was noted to have a webbed neck with a low hairline and facial asymmetry. CT and MRI showed multiple cerebral infarctions as well as a mass lesion in the posterior fossa. Cervical roentgenogram showed a fusion of C 2 and C 3 vertebrae. The tumor was totally removed via a suboccipital approach, and the diagnosis was a dermoid cyst. The present patient had not only dermoid cyst and Klippel-Feil syndrome but also hypertrophy of the zygomatic bone. The pathogenesis of the Klippel-Feil syndrome is presumed to be an intrauterine defect, with a failure of segmentation of mesodermal somites. The zygomatic bone is also derived from the mesoderm somites at early fourth week, too. From these points of view, the disturbance in the mesoderm before the fourth week of gestation might have played an important role in causing a dermoid cyst.