Brain anomalies found in 18 trisomy: CT scanning, morphologic and morphometric study.

Brain anomalies in 9 cases of cytogenetically proven 18 trisomy were reported. In addition to the various cerebral anomalies such as gyral or lobar abnormalities, hippocampal dysplasia, abnormal lateral geniculate body, agenesis or hypoplasia of the corpus callosum, absent or hypoplastic olfactory nerves, small optic tracts, and dysplasia of the inferior olivary nucleus, hypoplasia of the cerebellum and ventral pons was found in all cases. Cranial computed tomography was performed and revealed cerebellar and pontine hypoplasia with or without hypoplasia of the posterior cranial fossa as a characteristic finding in all 9 cases. A comparative morphometric study was done using age-matched controls. Macroscopically, the weight ratio of the cerebellum and brain stem to the whole brain was reduced compared with the controls. Microscopically, the thickness of the internal granular layer of the cerebellum was reduced especially at the convex area.