[Subarachnoid Hemorrhage]

Intracranial aneurysms or arterial dissections are major causes of subarachnoid hemorrhage(SAH). Early surgical or endovascular repair of the bleeding source is crucial because rebleeding mostly occurs within a few days after the initial attack. Radiological examination is an initial step for the appropriate diagnosis of ruptured intracranial aneurysms and arterial dissections. However, misdiagnosis may occur, especially in patients with minor bleeding or multiple aneurysms. In addition to computed tomography, magnetic resonance imaging, including FLAIR and SWI, and T2^*WI are useful for detecting minor SAH. Vessel-wall imaging has recently been applied to diagnosing the site of rupture in patients with multiple cerebral aneurysms or microaneurysms, but not to assessing the instability of unruptured cerebral aneurysms or intracranial arterial dissections. In this article, we discuss the current radiological modalities and their usefulness for diagnosing SAH.