Posterior fossa cysts: clinical, neuroradiological and surgical features.

Various types of neuroimaging investigations were performed in 26 patients with posterior fossa cysts. The results were retrospectively analyzed to facilitate differential diagnosis and clarify indications for surgery. Four major findings were obtained in this study. First, posterior fossa intra-arachnoid cysts were encountered more frequently than expected and were found to be surgically treatable. Second, although IV ventricular cysts were categorized as Dandy-Walker malformation, Dandy-Walker variant, and persistent Blake's pouch in this study, the distinctions of neuroimaging findings between these three types are uncertain. Third, the diagnostic criteria for mega cisterna magna were established, and it was found to be a surgically untreatable condition. Finally, in cases with the following neuroimaging findings, surgery appears to be indicated: (1) occipital bossing or petrosal scalloping with distortion or obliteration of cerebrospinal fluid (CSF) cisterns of the posterior fossa; (2) compression and deformity of the brain surrounding the cyst; (3) radioisotope and/or computed tomography cisternographic findings suggestive of disturbance of intracystic CSF circulation; (4) a non-communicating cyst.