[A case of thrombosed arteriovenous malformation in the brain stem]

A rare operative case of thrombosed arteriovenous malformation (AVM) in the brain stem was reported focusing on its differential diagnosis from cavernous malformation. A 49-year-old woman had developed pontine hemorrhage twice during the last two years. She was diagnosed by neurologists as having cavernous malformation in the brain stem, and then referred to our institute. Neurological examinations showed left hemi motor and sensory disturbance, right abducent palsy and right auditory disturbance. A computed tomography (CT) scan revealed a high density mass in the brain stem considered as a hematoma with slight enhancement. Magnetic resonance imaging (MRI) revealed a high intensity mass in T1 and T2 weighted MRI with marginal hemosiderin rim, but neither flow void sign nor enhancement effect was detected. Angiography depicted no abnormal vasculature in the posterior fossa. The patient underwent surgical resection of the lesion 43 days after a second hemorrhage. Midline sub-occipital craniotomy and the infrafacial route were chosen. Surgery was troubled by arterial bleeding, and pathological examination revealed a thrombosed AVM. She newly developed right facial palsy, right abducent palsy and disturbance of right conjugate gaze, but she is recovering step by step. Although the radiological feature of thrombosed AVM in the brain stem is similar to that of cavernous malformation, the operative procedure for thrombosed AVM is very difficult due to aggressive arterial bleeding that easily leads to surgical injury in the small surgical corridor in the brain stem. We reported a rare case that was pathologically well identified as thrombosed AVM in the brain stem focusing on its differential diagnosis and surgical treatment.