Subarachnoid Hemorrhage

When a brain aneurysm ruptures, it causes bleeding into the compartment surrounding the brain, the subarachnoid space and is therefore also known as a subarachnoid hemorrhage (SAH). Often the aneurysm heals over, bleeding stops, and the person survives. In more serious cases, the bleeding may cause brain damage with paralysis or coma. In the most severe cases, the bleeding leads to death.

What Happens to the Brain When an Aneurysm Bleeds?

In most cases, after a rupture the bleeding quickly stops. Blood in the cerebrospinal fluid (CSF) increases the pressure on the brain.

Damage to Brain Cells

Blood from an aneurysm can leak into the CSF (cerebrospinal fluid) in the space around the brain (subarachnoid space). The pool of blood forms a clot. Blood can irritate, damage, or destroy nearby brain cells. This may cause problems with body functions or mental skills.

Fluid Buildup in the Brain

Blood from a torn aneurysm can block CSF circulation. This can lead to fluid buildup and increased pressure on the brain. Because blood is sprayed around the base of the brain, the possibility of fluid buildup exists, causing hydrocephalus. The open spaces in the brain, called ventricles, may enlarge. It can make a patient lethargic, confused, or incontinent. To stop fluid buildup, a drain may be placed in the ventricles. The tube is called a ventriculostomy, and often drains into a bag at the patient’s bedside. This removes leaked blood and trapped CSF.


The blood around the base of the brain can also produce a problem called vasospasm. Vasospasm typically develops 5-8 days after the initial hemorrhage. Narrowing of the blood vessels can occur and at times not enough blood is supplied to the brain and a stroke may result. To treat vasospasm, blood pressure is often elevated with medicines. Certain medications are also given to try to ease vasospasm. Finally, catheters can be introduced inside the artery in an attempt to use balloons or medications delivered to the vessel directly to open up these narrowed vessels. Vasospasm does relax over several days.


SAH survivors usually have a much longer recovery time than unruptured aneurysm patients, as well as more serious deficits. Symptoms are proportional to the degree of hemorrhage. Patients who are comatose or semi-comatose after a hemorrhage have longer recoveries and have more significant neurocognitive problems as compared to patients with smaller hemorrhages or unruptured aneurysms.