[Sub, retro- and supracerebellar arachnoid cysts and pseudocyts in adults. Six observations].

Four arachnoïd cysts and two arachnoïd communicating pouchs in sub, retro and supra cerebellar situation are presented. These formations are rarely encountered in adults and distinction is often difficult from other cystic lesions whose structure is different (neuroglial and ependymal cysts). Intellectual slowing, mild ataxia or urinary disturbances, related to chronic hydrocephalus may be the only clinical symptoms. After computed tomography, isotopic cysternography, rather than metrizamide cysternography, must precise the possible communication between the cystic pouch and the subarachnoïd spaces, and the possible ventricular reflux. These informations are mandatory before selecting the treatment. In case of a non communicating cyst, total or subtotal excision should be preferred.