Subarachnoid hemorrhage

A subarachnoid hemorrhage, or subarachnoid haemorrhage in British English, is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. This may occur spontaneously, usually from a ruptured cerebral aneurysm, or may result from head injury.

Symptoms of SAH include a severe headache with a rapid onset (“thunderclap headache”), vomiting, confusion or a lowered level of consciousness, and sometimes seizures. The diagnosis is generally confirmed with a CT scan of the head, or occasionally by lumbar puncture. Treatment is by prompt neurosurgery or radiologically guided interventions with medications and other treatments to help prevent recurrence of the bleeding and complications. Surgery for aneurysms was introduced in the 1930s, but since the 1990s many aneurysms are treated by a less invasive procedure called “coiling”, which is carried out by instrumentation through large blood vessels.

SAH is a form of stroke and comprises 1–7% of all strokes. It is a medical emergency and can lead to death or severe disability—even when recognized and treated at an early stage. Up to half of all cases of SAH are fatal and 10–15% of casualties die before reaching a hospital, and those who survive often have neurological or cognitive impairment.


The initial steps for evaluating a person with a suspected subarachnoid hemorrhage are obtaining a medical history and performing a physical examination; these are aimed at determining whether the symptoms are due to SAH or to another cause. The diagnosis cannot, however, be made on clinical grounds alone; therefore medical imaging is generally required to confirm or exclude bleeding. The modality of choice is computed tomography (CT scan) of the brain. This has a high sensitivity and will correctly identify over 95% of cases—especially on the first day after the onset of bleeding. Magnetic resonance imaging (MRI) may be more sensitive than CT after several days. Within six hours of the onset of symptoms a single study has reported that CT is 100% sensitive.

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