• Tatsuya Ishikawa, Naoki Nakayama, Tetuyuki Yoshimoto, Takeshi Aoki, Shynsuke Terasaka, Mikio Nomura, Akihiro Takahashi, Satoshi Kuroda, and Yoshinobu Iwasaki.
• Department of Neurosurgery, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido 060-8638, Japan. teddish@saitama-med.ac.jp
• Surg Neurol. 2006 Sep 1; 66 (3): 269-75; discussion 275-6.

BackgroundRupture of cerebral aneurysms results in subarachnoid hemorrhage. In many cases, bleeding from aneurysms spontaneously arrests. Although bleeding from cerebral aneurysms has been reported to arrest from outside, bleeding from some aneurysms can arrest in different ways.MethodsBetween April 2002 and March 2004, we prospectively investigated mechanisms of spontaneous hemostasis in ruptured aneurysms by macroscopic examination when performing craniotomy and clipping surgeries.ResultsHemostatic mechanisms were investigated in 247 patients with ruptured aneurysm (77 men, 170 women; age range, 25-95 years). Hemostatic mechanisms were divided into 3 different patterns. In the most common pattern (79.4%), the surface of the aneurysm rupture point was sealed from the outside by a platelet plug or fibrin net (outside-arrest pattern). In some aneurysms (10.1%), a thrombus or platelet plug was attached to the rupture point from inside the aneurysm (inside-arrest pattern). In a very small number of aneurysms (1.6%), a naked thrombus covered the hole made on the arterial wall or small remnant of the aneurysmal dome (bursting pattern) The mechanism remained unclear in the remaining 8.9% of aneurysms. Multivariate analysis revealed that alert consciousness on admission (WFNS grade I) significantly associated with usual hemostasis (outside arrest pattern: OR, 3.8; 95% CI, 1.4-10.0; P = .008). Borderline association with usual hemostasis was found in aneurysms with a size of 5 or smaller than 5 mm (OR, 2.6; 95% CI, 0.99-7.1; P = .052).ConclusionsThe present preliminary study revealed that arrest of bleeding from a ruptured cerebral aneurysm does not always occur from outside the aneurysm. Unusual mechanisms of hemostasis are seen in approximately 12% of ruptured aneurysm. The outside-arrest-pattern aneurysm was more common for smaller aneurysms, and these patients tended to be of better grade. Further studies are necessary to explore the mechanism of hemostasis for ruptured cerebral aneurysms.

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