Two cases of dissecting aneurysm of the distal posterior inferior cerebellar artery: possible involvement of segmental mediolytic arteriopathy in the pathogenesis

Background: Dissecting aneurysm of the posterior inferior cerebellar artery (PICA) uninvolved with the vertebral artery is rare. The exact pathohistological diagnosis might result in ‘unknown’ because the underlying pathoanatomical features are, for a variety of reasons, not always identified. Case description: We report herein two cases of dissecting aneurysm harbored in different segments of the distal posterior inferior cerebellar artery. In our cases, after trapping the PICA at both just proximal and distal to the aneurysm, the abnormal portion was successfully resected with/without an end-to-end anastomosis. The first patient made a good recovery, while the other died 2 days after the surgery. Although its pathogenetic etiology was unidentified in the second case, the formation of dissecting aneurysm had resulted from a segmental mediolytic arteriopathy in the first case. Conclusion: This is the first report of a segmental mediolytic arteriopathy possibly being identified as causing an isolated dissecting aneurysm at this site.