POSTERIOR-FOSSA CYSTIC LESIONS - MAGNETIC-RESONANCE-IMAGING MANIFESTATIONS

Cystic lesions of the posterior fossa remain a controversial subject a s to clinical classification and diagnosis, especially for those in co mbination with other intracranial abnormalities. During the period of November 1985 to June 1991, 16 patients with cystic lesions of the pos terior fossa were retrospectively reviewed on neuroradiological evalua tion with MR images. The patients were 9 males and 7 females aged from 5 days to 15 years old (medium 1 year old). They were classified into three groups as Dandy-Walker cyst (group A, 5 patients), mega cistern a magna (group B, 4) and retrocerebellar pouch or cyst (group C, 7). N ine patients had associated intracranial anomalies, holoprosencephaly in 3 (group A, 3), dysgenesis of the corpus callosum in 4 (group A, 2; group C, 2), and occipital meningoceles in 2 (group C, 2). Hydrocepha lus or ventricular enlargement was found in 10 patients (group A, 5; g roup B, 2; group C, 3). Surgical treatment (cyst-peritoneal shunt or c ystectomy) was performed for 10 patients with clinical symptoms due to cyst. Postoperatively, clinical symptoms due to increased intracrania l pressure or hydrocephalus improved in 7 patients. For long-term resu lts, the cyst was reduced in 1 of 5 patients of group A and 2 of 5 of group C. Most of our patients have a poor prognosis because of the ass ociated intracranial anomalies or atrophy of the cerebellum. Multiplan ar MR images may provide sufficient evidence for the diagnosis of post erior fossa cysts, especially in the ease of rotation or upward displa cement of the cerebellar vermis. However, the cyst membrane, and the c ommunication of fluid between the cyst and the cistern, cannot be demo nstrated on MR images. Further investigation on these subjects and ind ications for surgical intervention is highly necessary.