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The authors studied 19 cases of posterior fossa cysts —14 of retrocerebellar cyst, three of unilateral cerebellar hemispheric cyst, and two of cerebellopontine angle cyst— all of which were presumptively diagnosed by means of axial computed tomography (CT) There were 15 children and four adults, ranging in age from 2.5 months to 65 years. Thirteen were male and six female. The patients underwent various neuroradiological tests, including sagittal reconstruction CT, radioisotope (RI) and/or CT cisternography, and angiography, as appropriate. Seventeen patients were treated surgically by excision of the outer wall of the cyst, followed in 15 cases by cystoperitoneal shunting. Retrospective classification of the 19 cases yielded seven communicating or non-communicating intra-arachnoid cysts, two Blake's pouch cysts, one Dandy-Walker cyst, two Dandy-Walker variants, one glioependymal cyst, one enlarged cisterna magna with communicating hydrocephalus, one fourth ventricular diverticulum, and four cases of large cisterna magna. In 10 of the 17 operated cases, the cyst disappeared, the cerebellum expanded, and the clinical symptoms abated.
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 fourth ventricular cysts were categorized as Dandy-Walker cyst, Dandy-Walker variant, and Blake's pouch cyst in this study, the neuroradiological distinctions between these three types are uncertain. Third, the surgical findings did not always corresponded to the preoperative classification. Finally, in cases with the following neuroradiological 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) RI and/or CT-cisternographic findings suggestive of disturbance of intracystic CSF circulation; and 4) a non-communicating cyst.
