ESSENTIALS OF DIAGNOSIS
Most aortic aneurysms are asymptomatic until rupture.
Abdominal aortic aneurysms measuring 5 cm are palpable in 80% of patients.
Back or abdominal pain with aneurysmal tenderness may precede rupture.
Rupture is catastrophic; hypotension; excruciating abdominal pain that radiates to the back.
Dilatation of the infrarenal aorta is a normal part of aging. The aorta of a healthy young man measures approximately 2 cm. An aneurysm is considered present when the aortic diameter exceeds 3 cm, but aneurysms rarely rupture until their diameter exceeds 5 cm. Abdominal aortic aneurysms are found in 2% of men over 55 years of age; the male to female ratio is 4:1. Ninety percent of abdominal atherosclerotic aneurysms originate below the renal arteries. The aneurysms usually involve the aortic bifurcation and often involve the common iliac arteries.
Inflammatory aneurysms are an unusual variant. These have an inflammatory peel (similar to the inflammation seen with retroperitoneal fibrosis) that surrounds the aneurysm and encases adjacent retroperitoneal structures, such as the duodenum and, occasionally, the ureters.
Although 80% of 5-cm infrarenal aneurysms are palpable on routine physical examination, most aneurysms are discovered on ultrasound or CT imaging as part of a screening program or during the evaluation of unrelated abdominal symptoms.
Aneurysmal expansion may be accompanied by pain that is mild to severe midabdominal discomfort often radiating to the lower back. The pain may be constant or intermittent and is exacerbated by even gentle pressure on the aneurysm sack. Pain may also accompany inflammatory aneurysms. Most aneurysms have a thick layer of thrombus lining the aneurysmal sac, but embolization to the lower extremities is rarely seen (eFigure 12–10).
CT angiography cross sectional image of a patient with a 5.5 cm aneurysm. Note the proximity of the aneurysm to the anterior abdominal wall. These vessels are easily palpable in 80% of patients.
The sudden escape of blood into the retroperitoneal space causes severe pain, a palpable abdominal mass, and hypotension. Free rupture into the peritoneal cavity is a lethal event.
In acute cases of a contained rupture, the hematocrit may be normal, since there has been no opportunity for hemodilution.
Patients with aneurysms may also have such cardiopulmonary diseases as coronary artery disease, carotid disease, kidney impairment, and emphysema, which are typically seen in elderly men who smoke. Preoperative testing may indicate the presence of these comorbid conditions, which increase the risk of intervention.