In the case of subarachnoid hemorrhage due to a rupture saccular aneurysm, an early CT scan will usually detect blood locally or diffusely in the subarachnoid spaces or within the ventricular system. Cerebral angiography using a catheter to place contrast medium directly in the large vessel of interest is currently the standard for diagnosing ruptured cerebral aneurysms as the cause of subarachnoid hemorrhage.

Subarachnoid hemorrhage often is fatal in a matter of only a few hours. The hemorrhage increases intracranial pressure to a level that approaches arterial pressure, causing a drop in cerebral blood flow and leading to loss of consciousness, coma, and death. If the patient survives the initial period, there is continued danger of rebleeding and ischemic stroke due to cerebral vasospasm. (Cerebral arteries may respond to blood in the subarachnoid space by constricting, thus diminishing blood flow to other parts of the brain.) Surgical repair is the treatment of choice for most aneurysms. It may involve occluding the neck of a balloon-shaped aneurysm with a metallic clip, wrapping the outside of the aneurysm, or inserting tiny thrombogenic metal coils into the aneurysm through a catheter. Surgery is usually performed as soon as possible because untreated, ruptured aneurysms have a high risk of rebleeding.

Prevention
Smoking and, to a lesser extent, hypertension are associated with aneurysmal subarachnoid hemorrhage. It is often recommended that large unruptured aneurysms be treated surgically. However at this time screening at-risk populations for aneurysms is of unproven value.