Giant arteriovenous aneurysm of the posterior fossa in a three-month-old infant.

A 3-month-old female infant presented a 20-day history of drowsiness and maturing deterioration. The neurological exam showed peripheric facial palsy on the right side and a brachiocrural hemiparesis on the left. A brain scan revealed a lesion of avascular content in the posterior fossa. The computed tomography scan showed hydrocephalus and a high-density lesion, nonenhanced after introduction of the contrast agent, compatible with a clot at posterior fossa level. Likewise, after contrast new images appeared which had not been seen previously, considered as afferent and efferent vascular elements to the lesion. The cerebral angiography showed an avascular lesion in the cerebellar vermis with important hypertrophy of arterial and venous elements, although no steal phenomena of neighbouring areas was evident. These findings, and the absence of cardiac failure, suggested the diagnosis, confirmed by surgery, of giant clotted arteriovenous malformation. The patient has done well postoperatively.