Aneurysms
An aneurysm is a bulge (dilation) in the wall of an artery, usually the aorta.
The bulge usually occurs in a weak area of the artery's wall. The pressure of blood inside the artery forces the weak area to balloon outward. If untreated, an aneurysm may rupture, resulting in internal bleeding.
Aneurysms can develop anywhere along the aorta. Three fourths of aortic aneurysms develop in the part that passes through the abdomen (the abdominal aorta), and the rest develop in the part that passes through the chest (thoracic aorta). Aneurysms can also develop in the arteries at the back of the knee (popliteal arteries), the main arteries of the thighs (femoral arteries), the arteries supplying the head (carotid arteries), the arteries supplying the brain (cerebral arteries), and the arteries supplying the heart muscle (coronary arteries). In older people, aneurysms are most likely to occur in areas where arteries branch (for example, where the abdominal aorta branches into the iliac arteries) or in areas of stress (for example, in the popliteal artery). Aneurysms may be round (saccular) or tubelike (fusiform). Most are fusiform.
The most common cause of aortic aneurysms is atherosclerosis, which weakens the wall of the aorta. Less common causes include injuries, inflammatory diseases of the aorta (aortitis), hereditary connective-tissue disorders such as Marfan syndrome, and some infectious diseases such as syphilis. In people with Marfan syndrome, an aneurysm is most likely to develop in the first part of the aorta, where it emerges from the heart (the ascending aorta). In older people, almost all aneurysms are associated with atherosclerosis. High blood pressure, which is common among older people, and cigarette smoking increase the risk of an aneurysm.
 See the figure Where Do Aortic Aneurysms Occur?
A blood clot (thrombus) often develops in the aneurysm because blood flow inside the aneurysm is sluggish. The clot may extend along the entire wall of the aneurysm. A blood clot may break loose (becoming an embolus), travel through the bloodstream, and block arteries. Aneurysms in the popliteal arteries are more likely to produce emboli than aneurysms in other arteries. Occasionally, calcium is gradually deposited in the wall of an aneurysm.
Abdominal Aortic Aneurysms
Abdominal aortic aneurysms are aneurysms that occur in the part of the aorta that passes through the abdomen (abdominal aorta).
Abdominal aortic aneurysms may occur at any age but are most common among men aged 50 to 80 years. Abdominal aortic aneurysms tend to run in families and to occur in people who have high blood pressure, especially those who also smoke. About 20% of abdominal aneurysms eventually rupture.
Symptoms
People who have an abdominal aortic aneurysm often become aware of a pulsing sensation in their abdomen. The aneurysm may cause pain, typically a deep, penetrating pain mainly in the back. The pain can be severe and is usually unrelenting if the aneurysm is leaking.
When an aneurysm ruptures, the first symptom is usually excruciating pain in the lower abdomen and back and tenderness in the area over the aneurysm. If the resulting internal bleeding is severe, a person may rapidly go into shock (see Section 3, Chapter 24). A ruptured abdominal aneurysm is often fatal.
Diagnosis
Pain is a useful but late clue. However, many people with aneurysms have no symptoms and are diagnosed by chance when a routine physical examination or an imaging procedure (such as x-rays or ultrasonography) is performed for another reason. Doctors may feel a pulsating mass in the midline of the abdomen. With a stethoscope placed on the middle of the abdomen, doctors can usually hear a whooshing sound (bruit) caused by turbulence as blood rushes past the aneurysm. However, in obese people, even large aneurysms may not be detected. Rapidly enlarging aneurysms that are about to rupture commonly hurt or feel tender when pressed during an abdominal examination.
Occasionally, an abdominal x-ray detects an aneurysm that has calcium deposits in its wall, but this procedure provides little other information. Other procedures are more useful for detecting aneurysms and determining their size. Usually, ultrasonography can clearly show the size of an aneurysm. If an aneurysm is detected, ultrasonography may be repeated every few months to determine if and how quickly the aneurysm is enlarging. Computed tomography (CT) of the abdomen, particularly if performed after a radiopaque dye is injected intravenously, can determine the size and shape of an aneurysm more accurately than ultrasonography but is more expensive. Magnetic resonance imaging (MRI) is also accurate but is more expensive than ultrasonography or CT.
Treatment
Aneurysms that are less than 2 inches (5 centimeters) wide rarely rupture. The only treatment required may be antihypertensive drugs (see Section 3, Chapter 22) to lower blood pressure. Imaging procedures are performed to estimate the rate of enlargement and determine when surgery will be necessary. At first, procedures are performed every 3 to 6 months, then at various intervals, depending on how quickly the aneurysm is enlarging.
Aneurysms that are wider than about 2½ inches (6 centimeters) rupture fairly commonly, so doctors usually recommend surgery, unless surgery is too risky for a particular patient. Surgery consists of inserting a synthetic graft to repair the aneurysm. There are two approaches. With the traditional approach, a general anesthetic is given, and an incision is made from below the breastbone to just below the navel. The graft is stitched into place in the aorta, the walls of the aneurysm are wrapped around the graft, and the incision is closed. This procedure takes 3 to 6 hours, and the hospital stay is usually 5 to 8 days. A newer, less invasive approach is called stent grafting. A regional (epidural) anesthetic, which causes loss of sensation only from the waist down, is used. Through a small incision made in the groin, a long, thin guide wire is threaded into the aorta to the aneurysm. A tube (catheter) containing the stent-graft (which resembles a meshed, collapsible straw) is guided over the wire and positioned inside the aneurysm. Then the stent-graft is opened, forming a stable channel for blood flow. This procedure takes 2 to 5 hours, and the hospital stay is usually 2 to 5 days. The risk of death during surgery to insert a graft is about 2 to 5%.
Rupture or threatened rupture of an abdominal aortic aneurysm requires emergency surgery. The risk of death during an operation for a ruptured aneurysm is about 50%. When an aneurysm ruptures, the kidneys may be injured because their blood supply is disrupted or because blood loss results in shock. If kidney failure develops after the operation, the chances of survival are very poor. Untreated ruptured abdominal aortic aneurysms are always fatal.
Thoracic Aortic Aneurysms
Thoracic aortic aneurysms are aneurysms in the part of the aorta that passes through the chest (thorax).
Thoracic aortic aneurysms are being identified more often than in the past because computed tomography (CT) of the chest to screen for other disorders is used more widely. In a common form of thoracic aortic aneurysm, the walls of the aorta degenerate (a condition called cystic medial necrosis), and the part of the aorta nearest the heart enlarges. This enlargement may cause a malfunction of the valve between the heart and the aorta (aortic valve), allowing blood to leak backward into the heart when the valve is closed. This disorder is called aortic valve regurgitation. About half of the people with this form of aneurysm also have Marfan syndrome. In the other half, no cause is apparent, although many of them have high blood pressure. Rarely, syphilis causes an aneurysm to form in the part of the aorta nearest the heart. Thoracic aneurysms that develop further away from the heart may result from a blunt injury to the chest.
Symptoms
Thoracic aortic aneurysms may become huge without causing symptoms. Symptoms result from the pressure of the enlarging aorta against nearby structures and thus depend on where the aneurysm develops. Typical symptoms are pain (usually high in the back), coughing, and wheezing. Rarely, a person coughs up blood because of pressure on or erosion of the windpipe (trachea) or nearby airways. Swallowing may be difficult if an aneurysm puts pressure on the esophagus, which carries food to the stomach. Hoarseness may result from pressure on the nerve to the voice box (larynx). A group of symptoms called Horner's syndrome (see Section 6, Chapter 96) may result from pressure on certain nerves in the chest. Symptoms include a constricted pupil, drooping eyelid, and sweating on one side of the face. Abnormal pulsations felt in the chest may indicate a thoracic aortic aneurysm. A displaced windpipe may be seen on chest x-rays.
When a thoracic aortic aneurysm ruptures, excruciating pain usually begins high in the back. It may radiate down the back and into the abdomen as the rupture progresses. The pain may also be felt in the chest and arms, as it is during a heart attack. A person can quickly go into shock (see Section 3, Chapter 24) and die because of internal bleeding.
Diagnosis
Doctors may diagnose a thoracic aortic aneurysm based on symptoms, or they may discover the aneurysm by chance during a routine physical examination. A chest x-ray taken for another reason may detect an aneurysm. Computed tomography (CT), magnetic resonance imaging (MRI), or transesophageal ultrasonography (in which the ultrasound probe is passed down the throat into the esophagus) is used to determine the precise size of the aneurysm. Aortography (an x-ray procedure performed after injection of a radiopaque dye that outlines the aneurysm) is usually performed to help doctors determine what type of surgery, if any, is needed. Magnetic resonance angiography or computed tomography angiography may be performed.
Treatment
If a thoracic aortic aneurysm is 2½ inches (6 centimeters) wide or larger, surgical repair using a synthetic graft is usually performed, as for an abdominal aortic aneurysm. Before surgery, a beta-blocker, calcium channel blocker, or another antihypertensive drug (see Section 3, Chapter 22) may be given to reduce the heart rate and blood pressure and thus reduce the risk of a rupture. The hospital stay is 5 to 8 days for traditional surgery (in which the chest in opened) and 2 to 5 days for stent-grafting (in which a collapsible graft is threaded to the aorta through a small incision, usually in the groin). In people who have Marfan syndrome, a rupture is more likely, so doctors may recommend surgical repair even for smaller aneurysms.
The risk of death is about 5 to 15% during repair of thoracic aortic aneurysms but is about 50% during an operation for a ruptured thoracic aneurysm. Untreated ruptured thoracic aortic aneurysms are always fatal.
Aneurysms in Other Arteries
Aneurysms may occur in arteries other than the aorta, such as the popliteal arteries (at the back of the knees), the femoral arteries (in the thighs), the coronary arteries (around the heart), and, rarely, the carotid arteries (in the neck). Older people are more likely to have aneurysms in these arteries than are younger people.
Many of these aneurysms result from a weakness present at birth (congenital) or arteriosclerosis. Others result from injuries caused by stab or gunshot wounds or from bacterial or fungal infections in the wall of the artery. Such infections usually start elsewhere in the body, typically in a heart valve (see Section 3, Chapter 29).
Most popliteal and femoral aneurysms do not produce symptoms. However, blood clots can form within the aneurysm, break loose (becoming emboli), and block an artery in the lower leg or foot. Emboli from carotid aneurysms can block an artery in the brain and cause a stroke. Popliteal, femoral, coronary, and carotid aneurysms rarely rupture.
Doctors may feel a pulsating mass in the affected artery. Ultrasonography or computed tomography (CT) can confirm the diagnosis. For popliteal aneurysms larger than 1 inch (2.5 centimeters) in diameter, surgery to repair the aneurysm is usually performed. Usually, femoral and carotid aneurysms are surgically repaired.
Aneurysms may also occur in the arteries of the brain (cerebral arteries). Rupture of a cerebral aneurysm may cause bleeding into the brain tissue (intracerebral hemorrhage), resulting in a stroke. Because cerebral aneurysms are near the brain and are usually small, their diagnosis and treatment differ from those of other aneurysms (see Section 6, Chapter 86). Infected aneurysms of the cerebral arteries are particularly dangerous, making early treatment important. Treatment often involves surgical repair, which is very risky.
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