Definition and Frequency

A subarachnoid hemorrhage (SAH) implies the pathologic escape of blood into the subarachnoid space. SAH may result from either traumatic or nontraumatic causes. The most common cause of SAH is head trauma.

Spontaneous rupture of a cerebral artery aneurysm is responsible for 95% of non trauma related SAH. Only a very small percentage of SAH are caused by the rupture of veins or capillaries. This course focuses on SAH resulting from the rupture of a cerebral artery aneurysm .

Cerebral artery aneurysm occurs where a weakness develops in the muscular wall (intimal layer) of a cerebral blood vessel. Blood pressure forces the remaining layers to expand outward, forming a thin walled balloon. The thin adventitia can rupture, allowing blood to enter the subarachnoid space under pressure, flooding cisterns, ventricles,sulci and spinal subarachnoid space.

It is estimated that approximately 10 to 15 million Americans have some type of an intracranial aneurysm. Most of these aneurysms are small, do not rupture during the person's life, and are identified only at the time of autopsy. However, each year in the United States, 30,000 people experience a subarachnoid hemorrhage due to non-trauma related rupture of a cerebral vessel.

SAH occurs most often in people between 20 and 60 years of age. SAH is more prevalent in women than in men, 1.6 women to 1 men. Approximately 15-20% of individuals with cerebral aneurysms have more than one aneurysm. Pediatric aneurysms account for only about 2% of all cerebral aneurysms.

Despite significant advances in diagnostic and surgical treatments, the prognosis for patients with a subarachnoid hemorrhage is poor. About 10% of individuals with aneurysmal SAH die before reaching medical attention. About 25% die within 24 hours with or without medical care. Forty percent of SAH patients die within the first week and about half die within six months. Of the survivors, 50 % will have serious disabilities. The economic and personal costs of acute care and rehabilitation for those with SAH are enormous.

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Spontaneous rupture of a cerebral aneurysm is responsible for 95% of non trauma related SAH.