The differential diagnoses for abdominal aneurysms include the causes of syncope, abdominal pain, back pain, and shock. The presentation of syncope with back pain or shock should strongly suggest aortic disease. However, the diagnosis will be difficult to make in shock or syncope without a significant complaint of pain. Other cardiac, abdominal, and retroperitoneal diseases need to be considered, including renal disorders, hepatobiliary disorders, and pancreatic disease. Unfortunately, some patients may appear well enough to receive benign diagnoses such as musculoskeletal back pain or enteritis and be discharged from the emergency department (ED).
The diagnosis may be further confused by coexisting pathology. Coronary artery disease and chronic lung disease are often present, and these features may distract the physician from the diagnosis of aneurysmal disease. This is especially true in patients without significant pain.
Aneurysms of large arteries other than the aorta may expand or rupture. Ileac aneurysms are notoriously difficult to diagnose because they may be confused with urologic, bowel, or groin disorders. Splenic artery aneurysms may present as undifferentiated shock or intraabdominal catastrophe. A rupture of the splenic artery has a poor prognosis owing to its intraperitoneal location.
Radiologic studies may be very helpful in confirming a ruptured AAA, but since radiographs often unnecessarily delay operative repair, the decision to obtain confirmatory studies must be made carefully.
Radiologic evaluation may include plain radiography, ultrasound ( Fig 54-1), or computed tomographic (CT). Plain abdominal films may show a calcified, bulging aortic contour implying the presence of an aneurysm. Approximately 65 percent of patients with symptomatic aortic aneurysmal disease will have a calcified aorta. Some propose that a cross-table lateral film of the abdominal aorta will have a higher yield for calcifications. 1 The lateral view will allow the aorta to be visualized without overlying the vertebral column. An AP projection may show an arch of calcification, most commonly on the patient's left. Rarely, a chronic aneurysm may erode into a vertebral body. Plain film cannot exclude the presence of AAA.
FIG. 54-1. Bedside ultrasound image of an abdominal aortic aneurysm. This aneurysm measures 6.5 cm.
Rapid bedside ultrasonography is ideal for unstable patients who cannot undergo CT scanning. A technically adequate ultrasound study has virtually 100 percent sensitivity for demonstrating the presence of an aneurysm and measuring its diameter.11 obesity or bowel gas may make the study difficult to perform. Rupture cannot be reliably seen.
CT with intravenous contrast is useful to demonstrate the anatomic details of the aneurysm and associated retroperitoneal hemorrhage. CT should be obtained on stable patients. Should unusual circumstances occur (such as the presence of other prominent acute abdominal conditions) and a CT become necessary, the patient should be accompanied by the surgeon, who could expedite an emergent operation if necessary.
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