[Aneurysms of the distal posterior inferior cerebellar artery; the report of 10 cases].

Non mycotic and non traumatic distal posterior inferior cerebellar artery (PICA) aneurysms are rare, but eleven aneurysms in ten cases were reported. They all originated from subarachnoid hemorrhage due to rupture of these aneurysms. The patients in these cases were all admitted within 5 days after the onset. The neurological state of four cases on admission was grade 4 or 5 in Hunt and Kosnik's grading system. Two patients of grade 5 died within 24 hours after the onset. The CT scan on admission revealed heavy subarachnoid hemorrhage mainly in the posterior fossa. In severe cases, ventricle hematoma, cerebellar hematoma and/or subdural hematoma were evident in the posterior fossa. The locations of these eleven aneurysms were as follows: On the bifurcation of the Telovelotonsillar segment in six cases. In the cortical segment in three cases. In the anterior medullary and tonsillomedullary segment in one case. Six saccular aneurysms were situated on bifurcations of parent arteries but three saccular aneurysms did not arise from bifurcations. Two of them were not from turning points of the arteries. One fusiform aneurysm situated on the bifurcation of telovelotonsillar segment was excised, and histologically shown to be a dissecting aneurysm with hypoplasia of elastic lamina and tunica media in the parent artery. Three cases were associated with small AVM located on the superior surface of the cerebellar vermis and fed mainly by the superior cerebellar artery (SCA) in two cases, and by SCA and PICA in one case. In these cases the hemodynamic stress on PICA did not seem to increase so remarkably.(ABSTRACT TRUNCATED AT 250 WORDS)