[Ruptured tiny middle cerebral artery aneurysm].

With new neuroimaging techniques, the detection rate of unruptured intracranial aneurysms has increased. While most detected aneurysms are small and left untreated because of the low risk of rupture, we still encounter many cases of small aneurysm rupture. Middle cerebral artery(MCA)aneurysms have lower risk of rupture compared to those in the anterior cerebral or internal carotid-posterior communicating arteries. Identification of small aneurysms with a high risk of rupture is important to improve management of these aneurysms. We report 10 cases of ruptured tiny(<3mm)MCA aneurysms. All patients underwent clipping and nine had good outcomes. One patient had poor outcome due to the worsening of chronic heart failure and kidney failure. A tiny aneurysm can rupture if the aneurysmal wall is fragile. Therefore, the fragility of the aneurysmal wall is an important predictive factor of rupture. Presently, however, it is difficult to determine when an operation for an unruptured tiny aneurysm is indicated; new neuroimaging techniques that detect the fragility of the aneurysmal wall are needed.