Pseudotumor syndrome in treated arachnoid cysts.

We report three patients with arachnoid cysts treated by cyst-peritoneal shunting in whom intracranial hypertension occurred during episodes of shunt malfunction. In one case this was associated with re-expansion of the arachnoid cyst, whilst in the other two cases this did not occur. The similarities between these two cases and patients with pseudotumor cerebri suggest a common pathogenic mechanism--specifically, a disturbance of the cerebrospinal fluid circulation.