Cerebral Aneurysm
A cerebral aneurysm is an abnormally dilated segment of a blood vessel surrounding the brain. In some cases, the entire blood vessel widens and expands to resemble a balloon-like structure.
Cerebral aneurysms occur in three to five percent of the general population, are more common in patients older than 30 and are almost twice as common in women than men. The exact cause of many cerebral aneurysms is not completely clear. In general, aneurysms are thought to arise from weakened areas in the wall of a blood vessel. Some aneurysms may occur as a congenital defect in the lining of the blood vessels, resulting in continued enlargement of the aneurysm over time. There appears to be a familial component to the development of aneurysms, as they are much more common in first-degree relatives, especially siblings. On rare occasions, multiple occurrences are reported in the same patient. Aneurysms frequently have a thin wall and are particularly prone to rupture or bleeding.
Several factors can induce weakening of the blood vessel wall, including infection, trauma, brain tumor and arteriovenous malformation (abnormal blood vessel development). Factors that have been shown to increase the risk of aneurysm rupture include smoking, excessive alcohol consumption and arteriosclerosis.
Risk of Aneurysm Rupture
Nearly 1/4 of all cerebrovascular deaths are due to ruptured aneurysms. The annual incidence of cerebral aneurysm rupture is approximately 7/100,000 persons. The peak incidence of aneurysm rupture occurs around age 50 to 60, although rare cases may occur in children and patients over 75. The risk of aneurysm rupture is approximately 0.05 to 2% per year, depending on the size and characteristics of the aneurysm.
Symptoms
Occasionally an enlarging aneurysm can cause symptoms (such as visual changes, seizures and facial pain) through the compression of surrounding neurologic structures. Unfortunately, symptoms frequently do not appear until the aneurysm has ruptured or bled. The rupture of a cerebral aneurysm is usually sudden and occurs without warning. Symptoms of a ruptured aneurysm may include loss of consciousness, severe headache with nausea or vomiting, stiff neck, difficulty moving any part of the body, numbness or decreased sensation in any part of the body, blurred vision, drooping eyelids, seizure and/or a change in mental status (such as a person becoming extremely lethargic).
Once an aneurysm ruptures, blood accumulates between the brain and the subarachnoid space (a thin wall surrounding the brain), resulting in a subarachnoid hemorrhage (SAH). As blood collects in this space, it compresses and damages the surrounding brain tissue. The tissue injury causes the surrounding blood vessels to be susceptible to vasospasm (an abnormal constriction of the blood vessels of the brain, which can result in additional tissue damage through diminished blood flow to the brain). The combined effect of bleeding and vasospasm can result in serious neurologic impairment or even death.
Treatment
Ruptured cerebral aneurysms require urgent medical attention. The goal is to control the immediate symptoms and prevent further bleeding. Upon arrival at the hospital, a patient's vital organ systems, such as respiration and circulation, are stabilized. Following this a thorough neurologic exam is performed to assess mental status and determine specific deficits. In the past, examination of fluid from the spinal cavity provided evidence of bleeding in the subarachnoid space. Today, three-dimensional X-rays (CT scans) or MRIs of the brain are the standard tests used to diagnose cerebral aneurysms. These scans often visualize bleeding (SAH) but may fail to pinpoint the exact site of the aneurysm. Video X-rays of blood vessels using injected dye (cerebral angiography) provide more detailed images of the blood vessels in the brain, often visualizing the exact location of the aneurysm.
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