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What are cerebral aneurysms?
What causes cerebral aneurysms?
How are aneurysms classified?
Who is at risk?
What are the dangers?
What are the symptoms of cerebral aneurysms?
How are cerebral aneurysms diagnosed?
How are cerebral aneurysms treated?
How can cerebral aneurysms be prevented?
What is the prognosis?
A cerebral aneurysm (also known as a brain aneurysm or an intracranial or intracerebral aneurysm) is a weak or thin spot on a blood vessel in the brain that balloons out and fills with blood. The bulging aneurysm can put pressure on a nerve or surrounding brain tissue. It may also leak or rupture, spilling blood into the surrounding tissue (called a hemorrhage). Some cerebral aneurysms, particularly those that are very small, do not bleed or cause other problems. Cerebral aneurysms can occur anywhere in the brain, but most are located along a loop of arteries that run between the underside of the brain and the base of the skull.
What causes cerebral aneurysms?
Most cerebral aneurysms are congenital, resulting from an inborn abnormality in an artery wall. Cerebral aneurysms are also more common in people with certain genetic diseases, such as connective tissue disorders and polycystic kidney disease, and certain circulatory disorders, such as arteriovenous malformations. Other causes include trauma to the head, high blood pressure, infection, tumors, atherosclerosis (a blood vessel disease in which fats build up on the inside of artery walls), cigarette smoking, and drug abuse. Some investigators have speculated that oral contraceptives may also increase the risk of developing aneurysms.
Aneurysms that result from an infection in the arterial wall are called mycotic aneurysms. Cancer-related aneurysms are often associated with primary or metastatic tumors of the head and neck. Drug abuse, particularly the habitual use of cocaine, can cause inflammation of blood vessels and lead to the development of brain aneurysms.
There are three types of cerebral aneurysm. A saccular aneurysm is a rounded or pouch-like sac of blood that is attached by a neck to an artery. Also known as a berry aneurysm (because it resembles a berry hanging from a vine), this most common form of cerebral aneurysm is typically found on arteries at the base of the brain, and most often occurs in adults. A lateral aneurysm appears as a bulge on one wall of the blood vessel, while a fusiform aneurysm is formed by the widening along all walls of the vessel.
Aneurysms are also classified by size. Small aneurysms are less than 11 millimeters in diameter, large aneurysms are 11-25 millimeters, and giant aneurysms are greater than 25 millimeters in diameter.
Brain aneurysms can occur in anyone and at any age. They are more common in adults than in children and slightly more common in women than in men. People with certain inherited disorders are also at higher risk.
All cerebral aneurysms have the potential to rupture and cause bleeding within the brain. The incidence of reported ruptured aneurysm is about 10 in every 100,000 persons per year which accounts for about 27,000 patients per year in the U.S. Rupture occurs most commonly in people between ages 30 and 60 years. Possible risk factors for rupture include hypertension, alcohol abuse, drug abuse (particularly cocaine), and smoking. In addition, the condition and size of the aneurysm affects the risk of rupture.
Aneurysms may burst and bleed into the brain, causing serious complications including hemorrhagic stroke, permanent nerve damage, or death. Once it has ruptured, the aneurysm may burst again and rebleed into the brain, and additional aneurysms may also occur. More commonly, rupture may cause a subarachnoid hemorrhage -- bleeding into the space between the skull and the brain.
A delayed but serious complication of subarachnoid hemorrhage is hydrocephalus, in which the excessive buildup of cerebrospinal fluid in the skull dilates fluid pathways called ventricles that can swell and press on the brain tissue. Another delayed post-rupture complication is vasospasm, in which other blood vessels in the brain narrow down and limit blood flow to vital areas of the brain. This reduced blood flow can cause stroke or tissue damage.
What are the symptoms of cerebral aneurysms?
Most cerebral aneurysms do not show symptoms until they either become very large or burst. Small, unchanging aneurysms generally will not produce symptoms, whereas a larger aneurysm that is steadily growing may press on tissues and nerves. Symptoms may include pain above and behind the eye, numbness, weakness, paralysis, dilated pupils, and vision changes. When an aneurysm hemorrhages, an individual may experience a sudden and extremely severe headache, double vision, nausea, vomiting, stiff neck, and/or loss of consciousness. Patients usually describe the headache as “the worst headache of my life” and it is generally different in severity and intensity from other headaches that patients may experience. Warning headaches may result from an aneurysm that leaks for days to weeks prior to rupture. Only a minority of patients have a warning headache prior to aneurysm rupture.
Other signs that a cerebral aneurysm has burst include nausea and vomiting associated with a severe headache, a drooping eyelid, sensitivity to light, and change in the level of awareness. Some individuals may have seizures or may lose consciousness briefly or go into prolonged coma. People experiencing a sudden and severe headache especially when it is combined with any other symptoms, should seek immediate medical attention.
How are cerebral aneurysms diagnosed?
Most cerebral aneurysms go unnoticed until they rupture or are detected by brain imaging that may have been obtained for another condition. Several diagnostic methods are available to provide information about the aneurysm and the best form of treatment. The tests are usually obtained after a subarachnoid hemorrhage, to confirm the diagnosis of an aneurysm.
Angiography is an invasive procedure used to analyze the arteries or veins, and can detect abnormalities in the anatomy of a blood vessel in the brain, head, or neck, such as an aneurysm. It is often considered the gold standard in the diagnosis of vascular problems in the brain, although with advances in technology other tests that are less invasive, such as CT angiography (CTA), are becoming more often utilized.
Computed tomography (CT) of the head is a fast, painless, and noninvasive diagnostic tool that can sometimes reveal the presence of a cerebral aneurysm and determine, for those aneurysms that have ruptured, the amount of blood that has leaked into the brain. This is often the first diagnostic procedure ordered by a physician following suspected rupture of an aneurysm. Occasionally a contrast dye is injected into the bloodstream prior to a CT scan, in order to produce sharper and more detailed images of blood flow in the brain and detect the presence of an aneurysm -- a test called CT angiography (CTA).
Magnetic resonance imaging (MRI) uses computer-generated radio waves (not x-rays) and a powerful magnetic field to produce detailed images of brain structures. Magnetic resonance angiography (MRA) is a modification of the traditional MRI which produces more detailed images of blood vessels which can show the size and shape of an unruptured aneurysm and can detect bleeding in the brain.
Cerebrospinal fluid (CSF) analysis may also be ordered if a ruptured aneurysm is suspected. Following application of a local anesthetic, a small amount of this fluid (which protects the brain and spinal cord) is removed from the subarachnoid space -- located between the spinal cord/nerves and the membranes that surround them in the lower back -- by surgical needle and tested to detect any signs of bleeding. In patients with suspected subarachnoid hemorrhage, this procedure is usually done in a hospital.
How are cerebral aneurysms treated?
Not all cerebral aneurysms burst. Some patients with very small aneurysms may be monitored to detect any growth or onset of symptoms and to ensure aggressive treatment of coexisting medical problems and risk factors. Each case is unique, and considerations for treating an unruptured aneurysm include the type/size/location of the aneurysm, risk of rupture, patient’s age/health/family medical history, and risk of treatment.
Two surgical options are available for treating cerebral aneurysms, both of which carry some risk to the patient (such as possible damage to other blood vessels, the potential for aneurysm recurrence and rebleeding, and the risk of post-operative stroke).
Microvascular clipping involves cutting off the flow of blood into the aneurysm. Under general anesthesia, a section of the skull is removed and the aneurysm is located. The neurosurgeon uses a microscope to isolate the blood vessel that carries the aneurysm and places a small metal clip on the aneurysm’s neck, halting its blood supply. The clip remains in the patient and prevents the risk of future bleeding. The piece of the skull is then replaced and the scalp is closed. Clipping has been shown to be highly effective, depending on the location, shape, and size of the aneurysm. In general, aneurysms that are completely clipped surgically do not return.
Endovascular embolization is an alternative to surgery. Once the patient has been anesthetized, the doctor inserts a hollow plastic tube (a catheter) into an artery (usually in the groin) and threads it, using angiography, through the body to the site of the aneurysm. Using a guide wire, detachable coils (spirals of platinum wire) or small latex balloons are passed through the catheter and released into the aneurysm. The coils or balloons fill the aneurysm, block it from circulation, and cause the blood to clot, which effectively destroys the aneurysm. The procedure may need to be performed more than once during the patient’s lifetime.
Following the treatment of the aneurysm itself, attention must be paid to the short-term and long-term potential complications of bleeding that was caused by the aneurysm. Underlying conditions, such as high blood pressure, should be treated; and anticonvulsants should be started to prevent seizures which may occur as a result of irritation of the brain from the blood. Vasospasm can be treated with a class of medications called calcium channel-blockers. Headache can be treated with analgesics and sedatives may be used if the patient is restless. Occasionally, if the blood blocks the absorption of cerebrospinal fluid (CSF), a temporary or permanent shunt may need to be placed to prevent the buildup of CSF which can cause harmful pressure on surrounding tissue. Patients also often need rehabilitative, speech, and occupational therapy to regain lost function and learn to cope with any permanent disability.
How can cerebral aneurysms be prevented?
There are no known ways to prevent a cerebral aneurysm from forming. People with a diagnosed brain aneurysm should carefully control high blood pressure, stop smoking, and avoid the use of stimulant drugs (such as cocaine). They should also consult with a physician about the benefits and risks of taking aspirin or other drugs that thin the blood, and can lead to more significant problems if a rupture occurs. Women should check with their doctors about the use of oral contraceptives.
An unruptured aneurysm may go unnoticed throughout a person’s lifetime. A ruptured aneurysm, however, may be fatal or could lead to hemorrhagic stroke, vasospasm (the leading cause of disability or death following a burst aneurysm), hydrocephalus, coma, or short-term and/or permanent brain damage.
The prognosis for persons whose aneurysm has burst is largely dependent on the age and general health of the individual, other preexisting neurological conditions, location of the aneurysm, extent of bleeding, and time between rupture and medical intervention. It is estimated that about 40% of patients whose aneurysm has ruptured do not survive the first 24 hours, and up to 25% die from complications within 6 months.
Some patients who experience subarachnoid hemorrhage may have permanent neurological damage from delayed complications such as hydrocephalus and vasospasm, making early diagnosis and treatment an important issue. About one third of patient who have a subarachnoid hemorrhage may recover with little or no neurological deficits.
Individuals who receive treatment for an unruptured aneurysm generally require less rehabilitative therapy and recover more quickly than persons whose aneurysm has burst. Recovery from treatment or rupture may take weeks to months.
