Infratentorial arachnoid cysts in children.

8 Children surgically treated for posterior fossa arachnoid cyst are described. In all the cases an enlarging head was the presenting sign; intracranial hypertension was evident in 6 patients; 2 children were clinically regarded as being affected by 'arrested' hydrocephalus. Preoperative subarachnoid lumbar infusion tests (8 cases) and prolonged intraventricular CSF pressure recordings (2 cases) demonstrated abnormal CSF dynamics in 6 cases. Ultramicroscopic examinations of the cyst wall (4 cases) suggest alterations in the anatomical arrangement of the arachnoid membrane, which supports the hypothesis of maldevelopment as the origin of the lesion.