Distal posterior inferior cerebellar artery saccular and giant aneurysms: report of two new cases and a comprehensive review of the surgically-treated cases.

Aneurysms of the distal posterior inferior cerebellar artery are rare comprising less than 0.5 to 3% of all aneurysms. The authors report two cases of distal PICA aneurysms: a case of a ruptured saccular aneurysm arising on the tonsillomedullary segment of the PICA and a case of a giant aneurysm arising on junctional site of lateral-medullary and tonsillo-medullary segments. In the first case subarachnoid and intraventricular hemorrhage was diagnosed by CT and four vessel-angiography visualized the aneurysm which was clipped successfully. In the second case MRI was suggestive for posterior fossa giant aneurysm; four vessel angiography confirmed the suspicion, detected distal PICA origin of the giant aneurysm and disclosed the association with a middle cerebral artery saccular aneurysm. Because of lacking of a clippable neck and important perforating vessels to brainstem, the aneurysm was trapped and excised successfully. The literature is exhaustively reviewed. Discussion regarding to distal PICA aneurysm distribution (location, age, sex, multiplicity and associated vascular anomalies), pathophysiology, clinical presentation, neuroradiological findings, surgery and outcome is presented.