• Yukihide Kanemoto, Yuhei Michiwaki, Kazushi Maeda, Yosuke Kawano, Naoki Maehara, Shintaro Nagaoka, and Hidefuku Gi.
• Department of Neurosurgery, Baba Memorial Hospital, Sakai City, Osaka, Japan. Electronic address: yukihidekane@mac.com.
• World Neurosurg. 2020 Jul 1; 139: e45-e51.

BackgroundTrue posterior inferior cerebellar artery (PICA) aneurysms outside the vertebral artery-PICA region are rare, with approximately 30 cases reported in just a few papers; no treatment paradigm has been advocated. The objective of this study was to present detailed clinical features and outcomes for several treatments for true PICA aneurysms and suggest an algorithm for treatment strategies.MethodsWe retrospectively analyzed outcomes of patients treated for PICA aneurysms with microsurgical and endovascular treatments. We also investigated the influence of several factors on the modified Rankin Scale score.ResultsCases with PICA aneurysms (n = 36) outside the vertebral artery-PICA region were identified angiographically. Aneurysm locations included anterior medullary (n = 7), lateral medullary (n = 10), tonsillomedullary (n = 4), telovelotonsillar (n = 12), and cortical (n = 3) segments of the PICA. Aneurysm morphology was as follows: dissecting: 22; fusiform: 6; and saccular: 8. On multivariate analysis, age (P = 0.028) and lack of vermian infarction (P =0.037) were associated with a significantly better prognosis. Prognosis was not significantly different for the 5 aneurysm locations and among the 4 treatment groups: clipping/coiling, trapping/parent artery occlusion, trapping/parent artery occlusion + bypass, and observation including external ventricular drainage.ConclusionsThis study suggests that factors associated with significantly better prognosis include age, clip/coil treatments, and no vermian infarction complication. A treatment algorithm for true PICA aneurysms was supported according to pretreatment H and K grade, PICA segments, aneurysm morphology, and 3 types of ischemia linked to the brainstem, cerebellar hemisphere, or vermis.Copyright © 2020 Elsevier Inc. All rights reserved.

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