[Aneurysms of the distal posterior inferior cerebellar artery--analysis of 14 aneurysms in 13 cases].

Thirteen cases of distal posterior inferior cerebellar artery (PICA) aneurysms are reported here. All the aneurysms were found after a subarachnoid hemorrhage. Dissecting aneurysm, incidentally found unruptured aneurysms, and aneurysms associated with arteriovenous malformation have been eliminated from this study. Characteristics for this type of lesion are a high rate of recurrent hemorrhage and rapid death due to direct compression of the brain stem, which clearly indicates the necessity of early surgery. Attention should be paid to the fact that angiography cannot always reveal aneurysms, especially when they are located in the peripheral PICA. One should also pay attention to multiple lesions and rapid growing acute subdural hematoma as initial findings for ruptured distal PICA aneurysm. Prognostic factors for these lesions are, vasospasm, especially when the aneurysm is located proximally in the PICA, and direct compression of the brain stem due to intraventricular hemorrhage when the aneurysm is located distally. It has been suggested that the pathogenesis of this lesion could be hemodynamic stress or embryogenesis. The shape and anomalous arterial structures of the 14 aneurysms presented here tend to agree with this suggestion. Our results suggest that the pathogenesis is hemodynamic stress that had developed due to embryological and/or arteriosclerotic factors.