[Diagnostic imaging of subarachnoid hemorrhage].

Subarachnoid hemorrhage is characterized by the extravasation of blood into the spaces covering the central nervous system which are filled with cerebrospinal fluid. The leading cause of non-traumatic subarachnoid hemorrhage is rupture of an intracranial aneurysm. Computed tomography (CT) scanning of the head should be the first examination performed in any patient with suspected subarachnoid hemorrhage. The characteristic appearance of extravasated blood is hyperdense. Head CT scanning can also demonstrate intraparenchymal hematomas, hydrocephalus and cerebral edema and can help predict the site of aneurysm rupture.