An abdominal aortic aneurysm is defined as an aorta ≥3.0 cm in diameter; repair is considered for an aneurysm ≥5.0 cm in diameter. Patients with an abdominal aortic aneurysm often (18%) have a first-degree relative with an aortic aneurysm, compared with <3% of those without aneurysm. Most patients are >60 years old, and males have an increased risk of the disease. Patients with aneurysms involving other major arteries and those with peripheral arterial disease are also at increased risk for aortic aneurysmal disease. The risk increases with the number of years of smoking and decreases with the number of years since quitting smoking.6 As smoking becomes less prevalent in the United States, abdominal aortic aneurysm deaths have decreased.7
Symptomatic abdominal aortic aneurysms may present with a variety of signs or symptoms that can mimic other primary diagnoses: syncope; flank, back, or abdominal pain; GI bleeding from an aortoduodenal fistula; extremity ischemia from embolization of a thrombus in the aneurysm; shock; or sudden death. Sudden death most commonly occurs from intraperitoneal rupture of the aneurysm, which leads to massive, rapid blood loss. Syncope without warning symptoms followed by severe abdominal or back pain suggests rupture of an abdominal aortic or visceral aneurysm with some temporary containment. Syncope is caused by rapid blood loss and a lack of cerebral perfusion. Patients may regain consciousness, but irreversible hemorrhagic shock follows without prompt diagnosis and intervention.
Back or abdominal pain is the most common presenting symptom with aortic aneurysm or rupture. The pain is classically severe and abrupt in onset, with about half of patients describing a ripping or tearing pain. Syncope occurs in about 10%. Many patients present with nonclassic sites of pain: flank, groin, isolated quadrants of the abdomen, and hip. Other common symptoms exist, such as nausea, vomiting, bladder pain, hip pain, or tenesmus.
Physical examination has only a moderate ability to detect a large abdominal aortic aneurysm. The sensitivity of abdominal palpation increases with aortic aneurysm diameter, ranging from 29% for a diameter of 3.0 to 3.9 cm to 50% for a diameter of 4.0 to 4.9 cm and 76% for a diameter of ≥5.0 cm.8 Tenderness to palpation of an aneurysm is commonly interpreted as a sign of aneurysmal expansion or rupture. However, a lack of tenderness does not indicate an intact aorta. Examination is difficult in the obese and the very thin.
The differential diagnoses include the causes of syncope, abdominal pain, chest pain, back pain, and shock. When seeing patient with abrupt back pain with syncope or shock, consider aortic aneurysm rupture. However, other cardiac, abdominal, and retroperitoneal diseases may be the cause, including renal disorders, hepatobiliary disorders, and pancreatic disease. If symptoms are insidious, it is possible that some patients may appear well enough and receive benign diagnoses, such as musculoskeletal back pain, and are discharged from the ED.
Diagnosis is confounded by coexisting pathology. Coronary artery disease and chronic lung disease are often present, and signs and symptoms of these disorders may distract the physician from the diagnosis of aneurysmal disease. This is especially true in patients without severe pain or with findings that seem congruent with another cause (e.g., ECG changes or dyspnea).
External signs of acute rupture are rare and include periumbilical ecchymosis (Cullen sign) or flank ecchymosis (Grey Turner sign). Retroperitoneal blood may dissect into the perineum or groin, causing scrotal or vulvar hematomas, or inguinal masses. Retroperitoneal blood may irritate the psoas muscle, triggering an "iliopsoas sign" (pain upon extension of the hip, typically with the patient lying on the opposite side). Blood may compress the femoral nerve and present as a neuropathy. The presence or rupture of an abdominal aortic aneurysm typically does not alter femoral arterial pulsations.9
Think of aortoenteric fistulas in patients with unexplained or high-volume upper or lower GI bleeding, especially in patients without liver disease. A history of aortic graft placement increases the risk of fistula. Fistulas most frequently involve the duodenum, with hematemesis, melenemesis, melena, or hematochezia. While massive, life-threatening bleeding is common, mild sentinel bleeding may be the first sign. Aortic aneurysms also may erode into the venous vasculature and form aortovenous fistulas, which cause high-output cardiac failure, decreased arterial blood flow distal to the fistula, and increased central venous volume.
Contained chronic abdominal aortic aneurysmal ruptures are not common. A retroperitoneal rupture may cause enough fibrosis to limit blood loss, and the patient may look well. The inflammatory response commonly causes pain, with pain continuing for an extended interval, clouding the diagnosis.
Imaging performed away from the bedside can delay emergency consultation and operative repair, so consult a surgeon early and before any transport for imaging when a symptomatic aneurysm is suspected.
Radiologic evaluation may include plain radiography (Figure 60-1), US (Figure 60-2), CT scanning (Figure 60-3), or MRI. Plain abdominal films may show a calcified and bulging aortic contour, implying the presence of an aneurysm (Figure 60-1). Approximately 65% of patients with symptomatic aortic aneurysmal disease have a calcified aorta, often better seen on a lateral view. An anteroposterior projection may show an arch of calcification, most commonly on the patient's left. Rarely, a chronic aneurysm may erode into a vertebral body and be seen on plain film. Plain film radiographs do not exclude the presence of abdominal aortic aneurysm or detect rupture and can be omitted in most patients.
Plain radiographic images of an abdominal aortic aneurysm. A. Lateral view of a calcified infrarenal aortic aneurysm. B. Posteroanterior view of a calcified infrarenal aortic aneurysm.
Bedside US image of an abdominal aortic aneurysm. This aneurysm measures 6.5 cm.
CT scan of a patient with a 12-cm abdominal aortic aneurysm. Calcification of the aortic wall is seen in the anterior aspect of the aneurysm. Evidence of hemorrhage and surrounding inflammation (arrow) is seen in the left side of the abdomen.
Bedside US (Figure 60-2) is ideal for initial screening and for patients with any hemodynamic compromise. Emergency US is noninvasive, easily deployed, and does not entail removal of the patient from the resuscitation area.10 A technically adequate US study has >90% sensitivity for demonstrating the presence of an aneurysm and measuring its diameter.10 Obesity, bowel gas, and abdominal tenderness may make the study difficult to perform. Measure aneurysms from the outside margin of one wall to the outside margin of the opposite wall in both the transverse (Figure 60-4) and longitudinal (Figure 60-5) planes. Identifying the superior mesenteric artery (Figure 60-6) allows distinguishing the aorta from the vena cava. An aortic diameter <3.0 cm excludes acute aneurysmal disease.
US image of an abdominal aortic aneurysm in the transverse plane.
US image of an abdominal aortic aneurysm in the longitudinal plane.
US image of an abdominal aortic aneurysm in the transverse plane showing the superior mesenteric artery (arrow) coursing parallel to the aorta.
CT scanning with IV contrast (Figure 60-3) best detects the anatomic details of the aneurysm and associated hemorrhage. Scan all stable patients with suspected abdominal aneurysmal disease or rupture. For those who cannot have IV contrast, unenhanced CT can reveal aneurysm size and retroperitoneal hemorrhage.