Large infratentorial multilocular arachnoid cyst.

Clinical and radiological findings in a 2-year-old boy with a large multilocular infratentorial arachnoid cyst are presented. The cyst was extended in the bilateral paracollicular and retrocerebellar region and was communicating with each other but not with the ventricular system. Associated with those cysts was a significant degree of hydrocephalus due to compression of the fourth ventricle. Delayed metrizamide CT scan showed totally isolated cysts from CSF circulation although the cystic content was determined as the CSF.