Ruptured partially thrombosed anterior inferior cerebellar artery aneurysms: two case reports and review of literature.

Aneurysms arising from the distal anterior inferior cerebellar artery (AICA) are very rare. When the parent artery is an AICA-posterior inferior cerebellar artery (PICA) variant, occlusion of the artery, even distal to the meatal loop, leads to a significant area of cerebellar infarction. We report two cases of ruptured partially thrombosed distal AICA aneurysms. In both cases, the parent artery was an AICA-PICA variant. The aneurysms were clipped in one case and trapped following occipital artery (OA)-AICA anastomosis in another case. It is important to keep the OA as a donor artery for revascularization in the treatment of the AICA-PICA variant aneurysms, especially when the absence of intra-aneurysmal thrombus is not comfirmed preoperatively.