[Distal aneurysm of the posterior inferior cerebellar artery--report of 3 cases].

The incidence of posterior fossa aneurysm is reported to be 4-15% of all intracranial aneurysms in large series. Most aneurysms of the posterior inferior cerebellar artery (PICA) arise at the origin of the PICA. However, aneurysms of the distal part of the PICA have only rarely been described. This report presents three cases of distal PICA aneurysm with subarachnoid hemorrhage. Two aneurysms were located in the superior retrotonsillar segment of the PICA in two cases, and another was located in the tonsillohemispheric branch in one case. Obliteration of these aneurysms was comparatively easily done by bilateral suboccipital craniectomy. Computerized tomography (CT) was done in two cases. CT scan of the second case revealed a hematoma in the cerebellar vermis, and that of the third case revealed hemorrhage in the fourth and third ventricles. These findings seem to be common in subarachnoid hemorrhage of this lesion and may suggest the rupture of distal PICA aneurysm.