Abdominal Aortic Aneurysm



Abdominal Aortic Aneurysm


Jerry Holleman



Mark Anderson is a 65-year-old retired Army officer who was in good health until 2 years ago, when a routine physical examination revealed a pulsatile, nontender upper midline abdominal mass.



What is the differential diagnosis of a pulsatile abdominal mass?

View Answer

Not every pulsatile mass is an aneurysm, although abnormal dilation of the aorta or one of its branch vessels (hepatic, splenic, superior mesenteric, renal, or iliac arteries) should be high on the list of possible diagnoses. A cystic or solid intraperitoneal or abdominal wall mass may also have referred aortic pulsations. A cystic mass in the small bowel mesentery, an inflammatory or neoplastic lesion in the colon, and a mass in the lesser sac related to previous pancreatitis may all have a presentation similar to Mr. Anderson’s, especially if the patient is thin.



What is an aneurysm?

View Answer

An aneurysm is a fixed, or permanent, enlargement of an artery to twice the normal diameter. True aneurysms have all three layers present, whereas false aneurysms or pseudoaneurysms have disruption of one or more of the walls of the artery. The normal abdominal aorta averages 1.5 to 2.5 cm in diameter, depending on the age and gender of the person (1).



What causes abdominal aortic aneurysms (AAAs)?

View Answer

Atherosclerosis is the cause of AAAs in approximately 95% of patients (2). The atherosclerotic process creates an intrinsic weakness in the arterial wall that leads to progressive dilation over time. Genetic factors also play a role in AAAs. The incidence of AAA in first-degree relatives of patients with AAA is approximately 25% (3). Less common causes of AAAs include trauma, syphilis, mycotic infection, congenital defects, Marfan’s syndrome, inflammation, and pregnancy. Aneurysms associated with reconstructive arterial surgery are being reported with increasing frequency (4).



How common are AAAs?

View Answer

AAAs are the most common of the atherosclerotic aneurysms, estimated to occur in as many as 2% of the elderly population in Western countries. Their incidence is increasing steadily, and they are the aneurysms most commonly diagnosed by physicians (5).

Mr. Anderson undergoes an abdominal ultrasound (US) examination, which reveals a 3.5-cm AAA. No further studies are performed, and he is monitored with serial US examinations.



Why is the size of an aneurysm important, and how does it guide surgical treatment?

View Answer

Rupture of an aortic aneurysm ranks 10th as the cause of death in men older than 55 years (6). Other complications of aneurysm include thrombosis, embolization, dissection, and obstruction of or erosion into an adjacent organ. Arterial wall tension, hence rupture risk, can be approximated by the law of La Place, in which tension is proportional to the product of the pressure and the radius (t = p × r).

The risk of rupture increases considerably with aneurysm size. For an aneurysm less than 4 cm in diameter, the risk of rupture is generally thought to be negligible, although it can occur. Aneurysms 4.0 to 5.5 cm in diameter have a 0.5% to 1.0% annual risk of rupture, whereas those 6 to 7 cm in diameter have a 6.6% annual risk of rupture. Aneurysms 7.0 cm or greater have 19% annual rupture risk (7). Elective repair should be considered in most patients with an aneurysm 5.5 cm or larger.



How should a patient such as Mr. Anderson be managed?

View Answer

A patient with a 3.5-cm aneurysm should be observed for symptoms and any evidence of growth. A 6-month follow-up US examination is routine. If the aneurysm is stable, yearly follow-up is recommended. Any indication of growth should prompt more frequent follow-up—for example, every 3 months.



What is the best radiologic technique for monitoring an aneurysm?

View Answer

There are essentially two options for surveillance: computed tomography (CT) and US. Magnetic resonance imaging is not cost-effective. CT is also helpful for evaluating other intraabdominal lesions. Both CT and US are noninvasive, but in most centers, US is accurate and cost-effective. Regardless of the test chosen, the same test must be used for follow-up examinations. Aortography and magnetic resonance angiography (MRA) are not used for surveillance; they are discussed later.

Mr. Anderson is reevaluated 1 year later, at which time the abdominal US examination shows that the maximal transverse diameter of the AAA is 3.7 cm and that it extends to the common iliac arteries bilaterally.



What is the average annual rate of growth of an AAA?

View Answer

US studies show that expansion rates vary from 2 to 8 mm per year, with an average of 4 mm annually (3). Traditional belief was that almost all aneurysms expand over time (8). However, it is now clear that some aneurysms show very little growth over a long period of follow-up, whereas others grow rapidly over a relatively short period (9). Individuals may often experience a staccato growth pattern in which periods of growth are followed by periods of stability. Certain risk factors, such as hypertension and chronic obstructive lung disease, are associated with rapidly growing aneurysms (10).

Mr. Anderson is scheduled for a repeat examination in 6 months, but he is lost to follow-up. He returns to the clinic 2 years later, at which time a follow-up abdominal US examination reveals enlargement of the aneurysm to 5.5 cm. Mr. Anderson is referred to surgery for further evaluation and elective surgical repair of his AAA.

Mr. Anderson does not have abdominal pain or tenderness, low back pain, extremity pain, hematuria, melena, or bloody stools. He has had no recent illness and has no history of angina, congestive heart failure, or cerebrovascular disease. He had a transurethral retrograde prostatectomy for benign prostatic hypertrophy 12 years ago. A physical examination shows Mr. Anderson appearing normal and in no apparent distress. His vital signs are blood pressure, 130/75 mm Hg; pulse, 78 beats per minute; respiratory rate, 18 breaths per minute; and temperature, 36.9°C.

The only abnormal finding on physical examination is a large immobile pulsatile mass palpated in the midepigastrium just above the umbilicus. The mass is not tender, and there is no audible bruit. The stools are guaiac negative. The laboratory data are hematocrit, 41%; leukocyte count, 7200 per mL; platelet count 284,000 per mL; blood urea nitrogen, 33 mg per dL; creatinine 1.1 mg per dL; electrolytes, normal; and coagulation tests, normal. The electrocardiogram and chest radiograph are normal. Plain abdominal radiographs show a calcified aortic wall with infrarenal aneurysmal dilation to approximately 4.5 cm.



What is the most frequent presentation of an AAA?

View Answer

AAAs are more common in men than in women by a ratio of 4:1, and they occur mainly in the sixth or seventh decade of life (3). In 75% of patients, the aneurysm is asymptomatic at the time of diagnosis. AAAs are most commonly diagnosed on routine physical examination or on imaging studies obtained for other reasons. With US, an increasing number of smaller aneurysms are being detected (11). When symptoms are present, the most common complaint is vague abdominal and back pain, which may be caused by expansion or rupture of the aneurysm. The pain frequently begins in the epigastrium and penetrates to the back. Tenderness on direct palpation of the aneurysm and flank pain are other signs of rupture. On rare occasions, patients have flank pain from ureteral obstruction or gastrointestinal bleeding from a primary aortoenteric fistula. Ureteral obstruction should raise suspicion of an inflammatory aneurysm (12).



What are the important findings from a physical examination?

View Answer

The physical examination is diagnostic in many cases. A large pulsatile immobile mass in the epigastrium is the most frequent finding. Because the bifurcation of the aorta is at the level of the umbilicus, the mass is usually at or above this level. Tenderness may be present on palpation, and a bruit may be found on auscultation of the abdomen. Distal pulses of the lower extremities may be diminished. Unfortunately, many aneurysms are not detected on physical examination, particularly in obese patients. In one study, only 15% of aneurysms in obese patients were diagnosed on physical examination and only 33% were palpable when the diagnosis was known (13).



What is the natural history of AAAs?

View Answer

The natural history of AAAs was described by Estes in 1950, before the advent of surgical repair (14). Of 102 patients with AAAs, only 67% were alive 1 year after diagnosis, 49% at 3 years, and 19% at 5 years. Rupture of the AAA caused the death of 63% of these patients. In a 1972 report on 156 patients who had been rejected for surgical repair, Szilagyi et al. (15) showed that among patients with aneurysms bigger than 6 cm, 43% died of aneurysm rupture and 37% died of myocardial infarction; among patients with aneurysms smaller than 6 cm, 36% died of myocardial infarction and 31% died of rupture.



What are the guidelines for recommending repair of an aneurysm?

View Answer

Treatment must be individualized, but the natural history of the condition provides general guidelines. Patients with an AAA larger than 6 cm should be considered for elective repair unless they have severe uncorrectable coronary artery disease (CAD) or severe chronic obstructive pulmonary disease (COPD). Most patients with an aneurysm that is 5.5 to 6 cm and no active CAD or COPD should also be considered for elective repair. The treatment of aneurysms smaller than 5 cm is controversial and probably should be rarely performed.



What is the appropriate preoperative radiologic workup for an aneurysm?

Sep 23, 2016 | Posted by in UROLOGY | Comments Off on Abdominal Aortic Aneurysm
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