Basal subarachnoid hemorrhage by rupture of arteriovenous malformation at the cerebellopontine angle.

A man in his late forties had lived as a recluse for more than ten years. He was found dead in his room. At autopsy, subarachnoid hemorrhage (SAH) was detected at the base of the brain, which weighed 1333 g. The cerebellar tonsil was swollen. The cerebral ventricle was enlarged and filled with blood. A hematoma was observed in the upper part of the left side of the cerebellar hemisphere. The location and size of SAH in this case indicated that the rupture of a cerebral aneurysm (CA) had occurred; however, CA was not detected. A mass of blood vessels buried in the hematoma was observed at the left cerebellopontine angle (CPA). The vascular lesion showed round-shaped blood vessels as well as flat-shaped vessels with the appearance of veins, but with elastic fibers indicative of arteries. The lesion was considered to be the nidus and was 5-8 mm in size. Feeding arteries appeared to be from the anterior inferior cerebellar artery (AICA). However, the draining vein and anastomotic parts of the artery and vein were not confirmed. Based on these histopathological features, this vascular lesion was diagnosed as arteriovenous malformation (AVM). A differential diagnosis between AVM at CPA and CA is needed in order to identify the source of non-traumatic SAH.