Developmental CSF cysts of the posterior fossa

Abstract

20 cases of operated developmental CSF cysts are surveyed: 8 Dandy-Walker syndromes and 12 extraaxial “arachnoid” cysts. A CSF shunt is the only possible operation for Dandy-Walker syndrome and a single shunt from the cyst is preferable to a double shunt; the success rate is 50%. Congenital extraaxial “arachnoid” cysts, which arise from a developmental anomaly of the roof of the hindbrain or primitive leptomeningeal spaces, must be differentiated from acquired arachnoid cysts. Those of this series fall into two groups: midline and lateral. Supravermian midline cysts resemble the Dandy-Walker syndrome in several respects, including the frequent recourse to a shunt operation and the uncertain distant prognosis, whilst the other extra-axial cysts usually simulate a cerebellar tumor. Lateral cysts may, however, present peculiar symptoms such as a homolateral motor deficit that does not always respond to surgery, and an oscillating symptomcomplex. Surgical removal is the treatment of choice both for subvermian midline and lateral cysts but subsequent shunting may be necessary to control persisting hydrocephalus. The long term prognosis is generally excellent for subvermian midline cysts but may be only fair for lateral cysts.