How does spontaneous hemostasis occur in ruptured cerebral aneurysms? Preliminary investigation on 247 clipping surgeries

Surg Neurol. 2006 Sep;66(3):269-75; discussion 275-6. doi: 10.1016/j.surneu.2006.03.030.


Background: Rupture 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.

Methods: Between April 2002 and March 2004, we prospectively investigated mechanisms of spontaneous hemostasis in ruptured aneurysms by macroscopic examination when performing craniotomy and clipping surgeries.

Results: Hemostatic 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).

Conclusions: The 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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Aneurysm, Ruptured / blood*
  • Aneurysm, Ruptured / surgery
  • Blood Coagulation* / physiology
  • Blood Platelets / physiology
  • Cerebral Angiography
  • Cerebral Arteries / diagnostic imaging
  • Cerebral Arteries / pathology
  • Cerebral Arteries / physiopathology*
  • Embolization, Therapeutic / instrumentation
  • Embolization, Therapeutic / methods
  • Female
  • Fibrin / physiology
  • Hemostasis* / physiology
  • Humans
  • Intracranial Aneurysm / blood*
  • Intracranial Aneurysm / surgery
  • Male
  • Middle Aged
  • Neurosurgical Procedures / instrumentation
  • Neurosurgical Procedures / methods
  • Prospective Studies
  • Subarachnoid Hemorrhage / blood*
  • Subarachnoid Hemorrhage / surgery
  • Subarachnoid Space
  • Surgical Instruments / standards
  • Treatment Outcome
  • Vascular Surgical Procedures / instrumentation
  • Vascular Surgical Procedures / methods


  • Fibrin