Aortic dissection and abdominal aortic aneurysms (AAAs) are important causes of morbidity and death that require rapid diagnosis and frequently require prompt operative repair to offer the patient any chance of survival. Diagnosing these conditions can be challenging and carries a high risk of misdiagnosis.
Four clinical scenarios arise regarding AAAs: acute rupture, aortoenteric fistula, chronic contained rupture, and an incidental finding. Although there are several other nonaortic large artery aneurysms that often require surgical repair by a vascular surgeon, they are aptly covered in Tintinalli's Emergency Medicine, 7th edition.
Acute rupturing AAA is a true emergency that, if not rapidly identified and repaired, will lead to death. The classic presentation is of an older (>60 years) male smoker with atherosclerosis who presents with sudden onset severe back or abdominal pain, hypotension, and a pulsatile abdominal mass. Patients may present with syncope or some variation of unilateral flank pain, groin pain, hip pain, or pain localizing to one quadrant of the abdomen.
Fifty percent of patients describe a ripping or tearing pain that is severe and abrupt in onset. Patients may have a tender pulsatile abdominal mass on physical examination, but the absence of pain does not imply an intact aorta. Obesity may mask a pulsatile abdominal mass. Nausea and vomiting are commonly present.
Shock may persist through presentation or may transiently improve due to compensatory mechanisms. Femoral pulsations are typically normal. Retroperitoneal hemorrhage may be appreciated as periumbilical ecchymosis (Cullen sign), flank ecchymosis (Grey-Turner sign), or scrotal hematomas. If blood compresses the femoral nerve, a neuropathy of the lower extremity may be present.
Aortoenteric fistulas, although rare, present as gastrointestinal bleeding, either a small sentinel bleed or massive life-threatening hemorrhage. A history of previous aortic grafting (eg, AAA repair) increases the suspicion. Because the duodenum is the usual site of the fistula, the patient may present with hematemesis, melenemesis, melena, or hematochezia.
Chronic contained rupture of AAA is an uncommon presentation. If an AAA ruptures into the retroperitoneum, there may be significant fibrosis and a limiting of blood loss. The patient typically appears quite well and may complain of pain for an extended period.
Discovering a previously undiagnosed asymptomatic AAA on physical or radiologic examination can be lifesaving. Those aneurysms larger than 5 cm in diameter (outer wall to outer wall) are at a greater risk for rupture, but all should be referred to a vascular surgeon.
Diagnosis and Differential
Although the diagnosis may be relatively straightforward in the setting of syncope, back pain, and shock with a tender pulsatile abdominal mass, the differential diagnosis varies depending on the presentation. Missed AAAs are most frequently misdiagnosed as renal colic. This life-threatening disease process should be considered in the differential diagnosis for any patient that presents with back pain, an intraabdominal process (pancreatitis, diverticulitis, mesenteric ischemia, etc), possible testicular torsion, or gastrointestinal bleeding disorders (eg, esophageal varices, tumors, or ulcers).
If the diagnosis of rupturing AAA is clear on clinical grounds, the operating vascular surgeon should immediately evaluate the patient. However, when the diagnosis is not entirely clear, confirming studies may be required. In the unstable patient, technically adequate bedside abdominal ultrasound has a >90% sensitivity for identifying AAA and can measure the diameter of the aneurysm (see Fig. 27-1). Be aware that aortic rupture or retroperitoneal bleed cannot be reliably identified with ultrasound. Obesity and bowel gas technically may limit the study. In the stable patient, computed tomography (CT) can identify the AAA and delineate the anatomic details of the aneurysm and any associated rupture. The role of plain radiography in the diagnosis of rupturing AAA in unclear; a calcified, bulging aortic contour is present in only 65% of patients with symptomatic AAA.
Bedside US image of an abdominal aortic aneurysm. This aneurysm measures 6.5 cm.
Emergency Department Care and Disposition
The primary role of the emergency physician is in identifying AAA.
For suspected rupturing AAA or aortoenteric fistula, prompt surgical consultation in anticipation of emergency surgery is critical. No diagnostic testing should delay surgical repair.
The patient is stabilized with large-bore intravenous access, judicious fluid administration for hypotension, treatment of hypertension (see Chapter 26), and typing and cross-matching of several units of packed red blood cells, with transfusion as needed. Because patients may rapidly deteriorate, those who undergo diagnostic testing should not be left unattended in the radiology department.
Pain control should be initiated with narcotic medications as compared to nonsteroidals due to medication induced platelet dysfunction. Control of pain is a compassionate intervention that may aid in control of blood pressure, but beware of hypotension.
For chronic contained rupturing AAA, consultation with a vascular surgeon for urgent repair and intensive care unit admission should be sought.
For AAA identified as an incidental finding, the patient potentially can be discharged home, depending on the aneurysmal size and comorbid factors. Telephone consultation with a vascular surgeon for admission or close office follow-up is usually adequate.