[External and internal hydrocephalus caused by an arteriovenous malformation in an infant].

In a 9 month-old infant, who displayed an epileptic seizure, the Brain CT-Scan shows a ventricular enlargement and a bilateral pericerebral effusion, associated with a left parieto-temporal arterio-venous malformation. Angiogram reveals a small angioma shunting the blood flow from the left middle cerebral artery into the lateral sinus. Intracranial pressure, recorded with a fontanellar transducer, is borderline. The angioma is excised and the operation, during which the subarachnoid location of the pericerebral effusion is confirmed, is followed by gradual subsiding of the internal and external hydrocephalus, that was caused by enhancement of the pressure in the venous sinuses. This case belongs to an infantile form of Benign Intracranial Hypertension, in which CT-Scan has to be interpreted cautiously, to avoid the pitfall of a wrong diagnosis of brain atrophy.