• Masaaki Hokari, Naoki Nakayama, Yusuke Shimoda, and Kiyohiro Houkin.
• Department of Neurosurgery, Hokkaido University Graduate School of Medicine, Sapporo, Japan. Electronic address: karimasa@med.hokudai.ac.jp.
• World Neurosurg. 2017 Jul 1; 103: 431-441.

BackgroundSome patients with aneurysm exhibit warning headaches without minor bleeding, and this could be caused by stretching of the aneurysm wall. Recently, our pathologic study observed subintimal fibrin deposition in a majority of the ruptured aneurysms. However, these findings also were observed in some unruptured aneurysms. In this report, 2 unruptured aneurysms exhibited subintimal fibrin, and interestingly, one of the patients experienced severe headache within 1 month before neuroimaging.ObjectiveWe performed pathologic analysis of unruptured aneurysms and collected their various clinical variables, including severe headache, to clarify the clinical characteristics of "dangerous" unruptured aneurysms.MethodsThis study included unruptured saccular aneurysm samples (n = 17) that were resected after clipping. We compared the differences in clinical variables, including warning headache, between aneurysms with and without fibrin deposition.ResultsFibrin deposition was present in the subintimal layer in 4 patients and in the periouter membrane in 4 patients. Three of the 4 former patients experienced warning headaches, and one presented aneurysm growth. Of the latter 4 patients, one exhibited aneurysm growth, whereas the others presented with relatively large aneurysms. In the remaining 9 aneurysms without fibrin deposition, monocyte infiltration was observed in one, all aneurysms were small, and no patients experienced warning headaches or aneurysm growth.ConclusionsSubintimal fibrin deposition is observed frequently in patients with aneurysm with warning headaches. These pathologic findings are clinically inspiring and may suggest that these aneurysms exhibit rapid stretching by newly formed aneurysms, which can result in rupture at an early stage.Copyright © 2017. Published by Elsevier Inc.

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