External hydrocephalus in adults. Report of three cases.

The authors report three adult patients who developed a symptomatic extraaxial collection of cerebrospinal fluid (CSF) after an intracranial hemorrhage. The fluid shifted from the extraaxial into the ventricular space as the patients' symptoms progressed. The symptoms resolved after placement of a ventriculoperitoneal shunt. External hydrocephalus, which is frequently observed in children, had not yet been described in adults. It is important to differentiate chronic subdural collections from external hydrocephalus, because ventricular CSF shunting increases the former while it is the treatment for the latter. The authors believe that symptomatic extraaxial fluid collections developed in these three adults during the early phase of posthemorrhagic hydrocephalus because the ventricles presented great resistance to distention at the onset of hydrocephalus. Animal experiments have led to the same result.