Spontaneous thrombosis of a vein of Galen aneurysm.

A 6-month-old girl , while being evaluated by her family physician for otitis media, was found to have a head circumference of 47 cm (99th percentile), with a tense and full anterior fontanelle. Past medical history was unremarkable, with normal developmental milestones. A noncontrast CT scan showed enlarged lateral and third ventricles and a homogeneous, high-attenuation mass in the region of the posterior portion of the third ventricle (Fig . 1A). No definite enhancement was seen after the infusion of IV contrast material. Bilateral carotid and vertebral angiography revealed enlarged venous structures compatible with a vein of Galen aneurysm fed solely by the left posterior cerebral artery (Fig . 1 B). These abnormal venous structures were smaller than the high-attenuation abnormality on CT, which led us to conclude that the lesion was partially thrombosed and readily amenable to surgical correction. The patient had a ventriculoperitoneal shunt, and 2 months later was admitted for craniotomy and clipping of the posterior cerebral artery. A preoperative scan done with and without IV contrast, however, demonstrated shunt malfunction with significant ventriculomegaly, necessitating shunt revision . The posterior third ventricular mass at this time was again identical on the noncontrast and contrast scans. It was now mixed in attenuation but unchanged in size from the earlier scan. The center of the malformation had areas that were hypodense, isodense, and hyperdense relative to brain . Peripherally, there was an area of calcification (Fig . 2A). Repeat cerebral angiography demonstrated slight mass effect in the posterior third ventricular region but no evidence of flow to the vascular malformation (Fig . 2B). Since further documentation of thrombosis of the aneurysm was demonstrated, the craniotomy was canceled . The patient has done well since that time. A follow-up CT 6 weeks after shunt revision , without IV contrast administration, showed mild persistent ventriculomegaly . The mass had decreased in size slightly and was somewhat irregular in outline. The walls of the mass were more densely calcified than on the previous examination and the