Causes
What can cause a cerebral aneurysm and how are they classified?
A cerebral 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). Cerebral aneurysms can be congenital, resulting from an inborn abnormality in an artery wall. They 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, artherosclerosis (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.
There are three types of cerebral aneurysm.
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. This type is also known as a berry aneurysm because it resembles a berry hanging from a vine. This is the most common form of cerebral aneurysm and is typically found on arteries at the base of the brain. It is most common in adults.
Lateral aneurysm-appears as a bulge on one wall of the blood vessel.
Fusiform aneurysm-is formed by the widening along walls of the vessel.
Diagnosis
Angiography is a dye test used to analyze the arteries or veins. This test 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. Following the injection of a local anesthetic, a flexible catheter is inserted into an artery and threaded throught 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. X-rays of the head are processed by a computer as two-dimensional cross-sectional images, or "slices," of the brain and skull. Sometimes 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 rain arteries.
Magnetic resonance imaging (MRI) used 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. Both procedures can show the size and shape of an unruptured aneurysm and can detect bleeding in the brain.
Cerebrospinal fluid analysis may be conducted 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 surgical needle and tested to detect any bleeding or brain hemorrhage.
Symptoms
Most cerebral aneurysms do not show symptoms until they either become very larger 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, severe headache, double vision, nausea, vomiting, stiff neck, and/or loss of consciousness.
Treatment
Microvascular clipping-this involves cutting off the flow of blood to the aneurysm. Under anesthesia, a section of the skull is removed and the aneurysm is located. The neurosurgeon uses a microscope to isolate the blood vessel that feeds the aneurysm and places a small, metal, clothespin-like clip on the aneurysm's neck, halting its blood supply. The clip remains in the person 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.
Occlusion-this involves the surgeon clamping off (occluding) the entire artery that leads to the aneurysm. This procedure is often performed when the aneurysm has damaged the artery. It is also sometimes accompanied by a bypass, in which a small blood vessel is surgically grafted to the brain artery, rerouting the flow of blood away from the section of the damaged artery.
Endovascular embolization-is a minimally invasive procedure that accesses the treatment area from within the blood vessel. During the procedure the patient is under anesthesia. A hollow plastic tube (catheter) is inserted into an artery (usually in the groin) and threaded through the vascular system to the site of the aneurysm in the brain using angiography (a procedure performed to view blood vessels in real time, after injecting them with a radioopaque dye that outlines them on x-ray). 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 coils are made of platinum so they can be visible via x-ray and be flexible enough to conform to the aneurysm shape. The procedure may need to be performed more than once during the person's lifetime.
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