Scarborough Vascular Ultrasound
Aortic Aneurysms (TAA & AAA)
An aneurysm is an area of a localized widening (dilation) of a blood vessel. (The word "aneurysm" is borrowed from the Greek "aneurysma" meaning "a widening").
An aortic aneurysm involves the aorta, one of the large arteries that carries blood from the heart to the rest of the body. The aorta bulges at the site of the aneurysm like a weak spot on an old worn tire.
The aorta is first called the thoracic aorta as it leaves the heart, ascends, arches, and descends through the chest until it reaches the diaphragm (the partition between the thorax and abdomen). The aorta is then called the abdominal aorta after it has passed the diaphragm and continues down the abdomen. The abdominal aorta ends where it splits to form the two iliac arteries that go to the legs.
Aortic aneurysms can develop anywhere along the length of the aorta. The majority, however, are located along the abdominal aorta. Most (about 90%) of abdominal aneurysms are located below the level of the renal arteries, the vessels that leave the aorta to go to the kidneys. About two-thirds of abdominal aneurysms are not limited to just the aorta but extend from the aorta into one or both of the iliac arteries.
Most aortic aneurysms are fusiform. They are shaped like a spindle ("fusus" means spindle in Latin) with widening all around the circumference of the aorta. (Saccular aneurysms just involve a portion of the aortic wall with a localized out pocketing).
The inside walls of aneurysms are often lined with a laminated blood clot that is layered like a piece of plywood.
Abdominal aortic aneurysms are most common after age 60. Males are 5 times more likely than females to be affected. This means men over 60 are at highest risk to develop an abdominal aortic aneurysm. Approximately 5% of men over age 60 develop an abdominal aortic aneurysm.
The most common cause of aortic aneurysms is "hardening of the arteries" called arteriosclerosis. At least 80% of aortic aneurysms are from arteriosclerosis. The arteriosclerosis can weaken the aortic wall and the pressure of the blood being pumped through the aorta causes expansion at the site of weakness.
Other causes of aortic aneurysms include:
Abdominal aortic aneurysms may cause pain. The pain typically has a deep quality as if it is boring into the person. It is felt most prominently in the lower back region. The pain is usually steady but may be relieved by changing position. The person may also become aware of an abnormally prominent abdominal pulsation. However, many aneurysms are without symptoms. They may become large and even rupture without warning.
Careful feeling of the abdomen by the doctor may reveal the abnormally wide pulsation of the abdominal aorta. This is characteristically felt on both sides of the aorta which is in the midline. Note that even large aneurysms can be very difficult to detect on physical examination in overweight people. Aneurysms that are rapidly enlarging and on the verge of rupture are often tender.
X-rays of the abdomen show calcium deposits in the aneurysm wall in about 90% of cases. Ultrasonography usually gives a clear picture of the extent and size of an aneurysm. Ultrasound has about 98% accuracy in measuring the size of the aneurysm. CT scanning of the abdomen, particularly with contrast medium, can be highly accurate in determining the size and shape of the aneurysm. MRI scanning is similarly accurate but is rarely necessary. Abdominal aortography shows the origin of the major blood vessels arising from the aorta and reveals the size and extent of any aneurysm. Contrast aortography is especially useful if there is extension of the aneurysm above the renal arteries and in delineating a mural thrombus (a clot clinging to the wall of the aneurysm).
The natural history of abdominal aortic aneurysms depends on their size. Rupture of aneurysms is uncommon when they are less than 5 cm wide. Rupture is far more common in aneurysms that are over 6 cm wide. Surgical repair is therefore usually recommended for all aneurysms over 6 cm wide. Elective repair is also generally recommended for aneurysms between 4 and 6 cm in patients who are good surgical risks.
Rupture is a feared problem. Half of all persons with untreated abdominal aortic aneurysms die of rupture within 5 years. Abdominal aortic aneurysms are the 13th leading cause of death in the U.S. Peripheral embolization of clot within the aneurysm can occur when a piece of clot comes loose and travels further out in the arterial system. This clot fragment can lodge in a smaller artery and block the flow of blood. Infection of aneurysms can occur from turbulent blood flow from the rough inner surface. Spontaneous blockage of the aorta can also occur.
Traditionally, repair of an aortic aneurysms has been surgical. The surgery has usually consisted of opening the abdomen, removing (excising) the aneurysm, and sewing a synthetic (Dacron) tube in its place.
More recently, "minimally invasive" procedures have been devised using stent grafts that can be guided to the site of the aneurysm without the need to cut open the abdomen. The first stent graft was installed in 1991 by Dr. Juan Parodi in Argentina.
A stent graft developed by Dr. Thomas Fogarty at Stanford is a Dacron tube inside a collapsed metal-mesh cylinder. To install the stent, a small incision is made in the thigh to gain access to the femoral artery. The stent, about 6 inches (15 cm) long, is guided inside a long plastic capsule through the arteries to the lower aorta. Once the stent is in place, the holding capsule is removed. Activated by heat, the stent expands like a spring and becomes anchored to the artery wall. The by-passed aneurysm then is shielded from the blood flow and typically shrinks over time.
According to a U.S. national multi-center study reported by Dr. Christopher Zari from Stanford in 1998, the "minimally invasive" installation of the stent graft carries a lower rate of complications and permits people to get back on their feet faster than traditional open surgery.
Threatened rupture of abdominal aneurysms is a surgical emergency. The operative risk for a ruptured aneurysm is about 50%. If kidney failure occurs after surgery, the prognosis (outlook) is particularly poor.
Rupture of an abdominal aneurysm is a catastrophe. It is highly lethal and is usually preceded by excruciating pain in the lower abdomen and back, with tenderness of the aneurysm. Rupture of an abdominal aneurysm causes profuse bleeding and leads to shock. Death may rapidly follow.