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The Following definitions are taken from the The Brain Aneurysm Report, a publication of The Brain Aneurysm Foundation.

 What is a Brain Aneurysm ?

The word "aneurysm" is derived from the Latin word "to widen". An aneurysm is the widening of an arterial wall, and sometimes this weak bulging spot can bleed.

 What Are Their Symptoms ?

Some aneurysms rupture or hemorrhage which may cause a severe, blinding headache often described as the "worst headache of my life" which becomes more unbearable every minute. Other symptoms may include loss of consciousness, vomiting, nausea, stiff neck, blurred vision, sensitivity to light, sensitivity to sound, inability to speak or understand words, weak or paralyzed limbs, seizures, high blood pressure, or a low pulse. Pain may also be felt in the entire head, forehead, neck, and shoulders.

Many people live their entire lives with an undiagnosed, unruptured aneurysm which is small and causes no problems or bleeding. Some unruptured aneurysms do cause symptoms depending on their size and location in the brain. One or more of the following are common symptoms; an enlarged pupil, a droopy eyelid, pain above or behind the eye, localized or mild headache, attacks of giddiness, uncertain gait, or a temporary visual disturbance.

Some aneurysms do have a small amount of occasional bleeding which may cause the gradual onset of these signs: general headache, nausea, neck pain, vomiting, lapses of consciousness, ringing in the ears, dizziness, or black spots in the visual field.

Prior to rupture, only 10% - 15% of all aneurysms are able to be diagnosed from their clinical symptoms and signs. 85% - 90% of aneurysms are not diagnosed until after they have ruptured.

 Who Can Have One ?

No study has been undertaken to determine the incidence of brain aneurysms in the general population. However, in several large autopsy studies the frequency of brain aneurysms has been reported to range from .2% - 9.9%. Several smaller studies suggest that the incidence of brain aneurysms in the general population is 1% - 5%. Lastly, one study estimates that as many as 400,000 people in the U.S. may have a brain aneurysm of significant size.

The highest incidence of brain aneurysms is in people in their 50's and 60's. Sixty-two percent of all first cases are diagnosed between 40-65 years of age and hemorrhages are prevalent between the ages of 50-54. It is rare for an aneurysm to occur in the very young or very old.

Aneurysm rupture usually causes subarachnoid hemorrhage (SAH). With an SAH, the blood from the hemorrhage goes between the brain and the brains covering. It has been estimated that 6 in 100,000 will have an SAH or 25,000 people annually. Above the age of forty, there is a higher incidence of SAH in women than in men. However, under the age of forty more men than women are affected.

A third of patients who suffer a subarachnoid hemorrhage will survive with a good recovery: a third will survive with substantial disabilities and a third will die as a result of the hemorrhage.

 What Causes Them ?

The cause of brain aneurysms is poorly understood. The diagnosis of familial aneurysm is an inherited tendency to develop aneurysms that occurs in 5 to 7 percent of patients with aneurysms. Defects in the muscle layers of the blood vessel wall have been found on autopsy examinations. These abnormalities have been found in people who had aneurysms and people who did not, so there are other considerations such as socio-economic background, diet, and general health status that also need to be considered. Certain rare diseases are known to weaken blood vessel walls which may lead to the development of an aneurysm. Marfan"s Syndrome, Pseudoxanthoma elasticum, and Ehlers-Danlos Syndrome are some of these diseases. Other diseases are Polycystic Kidney Disease and Fibro-muscular Dysplasia.

A bacterial or fungal infection is a rare cause of an aneurysm and occurs in only 2.6% - 6% of all brain aneurysm cases. The infection damages the blood vessel wall by weakening it, causing an aneurysm to develop that may eventually rupture.

The aging process is another predisposing factor of aneurysm formation. Some studies suggest that degenerative changes take place within the blood vessel wall causing it to weaken with age, therefore increasing the liklihood of an aneurysm developing.

 References:

"Impact of Unruptured Intracranial Aneurysms on Public Health in the U.S." David O. Wiebers, M.D., et al Stroke, Vol. 23, Number 10. Oct. 1992. pp 1416-1419.

"Intracranial Aneurysms." Paul J. Camarata, M.D., et al. Investigative Radiology, Vol. 28, Number 4. April 1993. pp 373-382.

Handbook of Clinical Neurology. Vol. 12, 1972. Richard Heidrich. pp 85-128.

The Clinical Practice of Neurological and Neurosurgical Nursing. 3rd edition. 1992. Joanne V. Hickey pp 541-552.

"Infectious Intracranial Aneurysms." Christopher E. Clare, M.D., et al. Neurosurgery Clinics of North America. Vol. 3, Number 3. July 1992. pp 551-566.

Spontaneous Intracererbal and Infratentorial Hemorrhage. J.P. Custel et al. Neurological Surgery. 3rd edition. Vol. 3, 1990. pp 1890-1916.

Neurologic Clinics. Vol. 3, Number 2, 1985. Robert M. Crowell. pp 292-306.

"Intracerebral Hemorrhage More Than Twice As Common As Subarachnoid Hemorrhage." Joseph P. Broderick et al. Journal of Neurosurgery. Vol. 78, Feb. 1993. pp 188-191.