A cerebral aneurysm (also known as 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 a cerebral aneurysm?
Cerebral aneurysms can be 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 (snarled tangles of arteries and veins in the brain that disrupt blood flow).
Other causes include trauma or injury to the head, high blood pressure, infection, tumors, atherosclerosis (a blood vessel disease in which fats build up on the inside of artery walls) and other diseases of the vascular system, cigarette smoking, and drug abuse. Some investigators have speculated that oral contraceptives may 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 tumors of the head and neck. Drug abuse, particularly the habitual use of cocaine, can inflame blood vessels and lead to the development of brain aneurysms.
How are aneurysms classified?
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 or stem to an artery or a branch of a blood vessel. 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. Saccular aneurysms occur most often 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 (about the size of a large pencil eraser), larger aneurysms are 11-25 millimeters (about the width of a dime), and giant aneurysms are greater than 25 millimeters in diameter (more than the width of a quarter).
Who is at risk?
Brain aneurysms can occur in anyone, 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 (about 30,000 individuals per year in the U.S.), 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.
What are the dangers?
Aneurysms may burst and bleed into the brain, causing serious complications, including hemorrhagic stroke, permanent nerve damage, or death. Once it has burst, the aneurysm may burst again and bleed into the brain, and additional aneurysms may also occur. More commonly, rupture may cause a subarachnoid hemorrhage— bleeding into the space between the skull bone 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 postrupture complication is vasospasm, in which other blood vessels in the brain contract and limit blood flow to vital areas of the brain. This reduced blood flow can cause stroke or tissue damage.
What are the symptoms?
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, or paralysis on one side of the face; 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. Individuals usually describe the headache as “the worst headache of my life” and it is generally different in severity and intensity from other headaches people may experience. “Sentinel” or warning headaches may result from an aneurysm that leaks for days to weeks prior to rupture. Only a minority of individuals have a sentinel 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 mental status or level of awareness. Some individuals may have seizures. Individuals may lose consciousness briefly or go into prolonged coma. People experiencing this “worst 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 a dye test used to analyze the arteries or veins. An intracerebral angiogram can detect the degree of narrowing or obstruction of an artery or blood vessel in the brain, head, or neck, and can identify changes in an artery or vein such as a weak spot like an aneurysm. It is used to diagnose stroke and to precisely determine the location, size, and shape of a brain tumor, aneurysm, or blood vessel that has bled. This test is usually performed in a hospital angiography suite. Following the injection of a local anesthetic, a flexible catheter is inserted into an artery and threaded through the body to the affected artery. A small amount of contrast dye (one that is highlighted on x-rays) is released into the bloodstream and allowed to travel into the head and neck. A series of x-rays is taken and changes, if present, are noted.
Computed tomography (CT) of the head is a fast, painless, noninvasive diagnostic tool that can reveal the presence of a cerebral aneurysm and determine, for those aneurysms that have burst, if blood has leaked into the brain. This is often the first diagnostic procedure ordered by a physician following suspected rupture. X-rays of the head are processed by a computer as two-dimensional cross-sectional images, or “slices,” of the brain and skull. Occasionally a contrast dye is injected into the bloodstream prior to scanning. This process, called CT angiography, produces sharper, more detailed images of blood flow in the brain arteries. CT is usually conducted at a testing facility or hospital outpatient setting.
Magnetic resonance imaging (MRI) uses computer-generated radio waves and a powerful magnetic field to produce detailed images of the brain and other body structures. Magnetic resonance angiography (MRA) produces more detailed images of blood vessels. The images may be seen as either three-dimensional pictures or two-dimensional cross-slices of the brain and vessels. These painless, noninvasive procedures can show the size and shape of an unruptured aneurysm and can detect bleeding in the brain.
Cerebrospinal fluid analysis may 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 and the membranes that surround it—by a spinal needle and tested to detect any bleeding or brain hemorrhage. In individuals with suspected subarachnoid hemorrhage, this procedure is usually done in a hospital.