Abdominal Aortic Aneurysm

  • Written By: Jacob Manteuffel, MD, Henry Ford Hospital, Detroit, Michigan
  • Edited By: Rahul Patwari, MD, Rush University, Chicago, Illinois

Abdominal Aortic Aneurysm Objectives

  • Describe the classic triad of ruptured AAA
  • Discuss imaging modalities for diagnosis of AAA
  • Describe the emergency department course and treatment after diagnosis of ruptured AAA is reached
  • Understand which patients diagnosed with AAA can be safely discharged

Abdominal aortic aneurysms can be found on autopsy in up to 4% of people aged 50 years or greater, up to 10% of elderly men (age > 65), and up to 15% of men with peripheral vascular disease. Patients with a ruptured AAA may present to an emergency department with a chief complaint of abdominal, back, or flank pain.

Common misdiagnoses of patients with ruptured AAAs include renal colic, pancreatitis, bowel ischemia, diverticulitis, cholecystitis, bowel obstruction, myocardial infarction, and musculoskeletal back pain.

Ruptured AAA is fatal unless treated surgically, and even with surgical intervention mortality is approximately 50%.

Classic Presentation

Ruptured AAA

The classic triad of ruptured AAA is:

  • pain
  • hypotension
  • pulsatile abdominal mass

The pain is usually acute, severe and constant and located in the abdomen, back, or flank. The pain can radiate to the chest, thigh, inguinal region, or scrotum.

A ruptured AAA can also be associated with nausea and vomiting and can cause near-syncope, syncope, or altered mental status.

In any patient who presents with a known AAA with the acute onset of symptoms, the presumptive diagnosis is aneurysm rupture.

On physical exam, a tender pulsatile, expansile abdominal mass at or above the level of the umbilicus is diagnostic. Seventy-five percent of aneurysms 5 cm and larger can be palpated. A continuous abdominal bruit and a palpable abdominal thrill are suggestive of an aortovenous fistula. Heme-positive or grossly bloody stools can be indicative of an aortoenteric fistula.

Unruptured AAA

Most patients diagnosed with AAA are asymptomatic and are discovered incidentally on physical exam or through a radiology study of the abdomen done for an unrelated reason. Patients may complain of abdominal, back, or flank pain with a stable, intact AAA. However, the pain usually has a gradual onset and a dull quality. Patients may also complain of abdominal mass, fullness, or the sensation of pulsations.

Initial Actions & Primary Survey

When a patient has a known or suspected ruptured AAA, the patient should be considered unstable, regardless of initial vital signs or hemoglobin.

Manage airway and breathing appropriately. Most of the resuscitative effort will be directed toward potential circulatory collapse.

Two large-bore intravenous lines should be established with blood sent to the lab for type and crossmatch in anticipation of large transfusion requirement.

There is no agreed upon resuscitation strategy for hypotensive patients with ruptured AAAs. Hypotensive patients may benefit from a slowing in the rate of hemorrhage and clot formation. On one hand, large volumes of crystalloid solution can cause further bleeding (by dislodging clots) and causing a dilutional coagulopathy. On the other hand, prolonged hypotension can cause myocardial infarction, respiratory failure, renal failure. Therefore a target systolic blood pressure of between 90 and 100 mm Hg is reasonable to prevent these complications.

Diagnostic Testing

Hemodynamically unstable patients with a known or suspected ruptured AAA should be transferred to the operating as soon as possible. Radiology studies should be kept to a minimum. If the patient is not hypotensive, more time and studies can be used to confirm the presence of an AAA.

Laboratory Testing

Laboratory testing can be done to support the diagnosis of ruptured AAA. A hemoglobin and hematocrit can be helpful to diagnose an aortoenteric fistula if the hemoglobin is low. Coagulation studies should be ordered in these cases and any coagulopathy should be reversed if necessary. Electrolytes and urinalysis are can also he useful for the detection of blood or renal failure, but could confuse the diagnosis with ureterolithiasis. In the work up of an undifferentiated abdominal pain, a lipase and liver function tests may be useful as well.

Ultrasound

Ultrasonography is the ideal study for detection of AAA. It is an extremely sensitive test and can be done at the patient’s bedside. However, the aorta is sometimes not well visualized because of obesity or bowel gas. This test is also more operator dependent than other diagnostic modalities.

The image to the left shows a AAA with a thrombus. Click the image to see the video.

Computed Tomography (CT)

Computed tomography (CT) is extremely accurate in determining whether or not an AAA is present. CT is less operator dependent than ultrasound and is more accurate in detecting extraluminal blood. Intravenous contrast is desirable, but not essential, for emergency department exams. It raises the level of detail of the exam, but worsens nephropathy caused by hypotension.

However in unstable patients, radiology studies should be kept to a minimum. If the patient is not hypotensive, these patients should not be sent to the operating room. In this case, bedside ultrasound (if available) can be used to confirm the presence of an AAA.

Plain Radiographs

Plain film radiographs of the abdomen can be diagnostic if ultrasound and CT are not readily available. A curvilinear calcification of the aortic wall or a paravertebral soft tissue mass can be found.

So how do you make the diagnosis?

Hemodynamically unstable patients with signs and symptoms of ruptured AAA should be given presumptive diagnosis of ruptured aneurysm and treated as such.

In other patients, reviewing radiographic studies with appropriate clinical correlation is warranted. Rarely a CT may falsely negative for rupture of an AAA. Patients should be considered to have an imminent rupture of the AAA if the history and physical examination is consistent with a ruptured AAA, but CT findings indicate an intact AAA.

Treatment

Resuscitation should have been started during your primary survey. Patients with ruptured AAA may require crystalloid and blood products. Remember that O-negative blood is an option while waiting for crossmatched blood to become available. By the time cross matched blood is available,the patient should be in the operating room.

Treatment of a ruptured AAA requires emergent surgical repair. Contact the vascular surgeons early, often before definitive diagnosis is made. Surgical treatment should not be delayed for preoperative volume resuscitation.

Incidental, asymptomatic AAAs found during an emergency department visit can sometimes be observed or repaired electively.

Disposition

An acutely symptomatic patient with AAAs requires hospital admission and surgical repair.

An unstable patient with AAA requires emergent surgical consultation and transfer to the operating room. Any delay in surgical care will result in an increased mortality.

A patient with an AAA diagnosed in the emergency department and discerned not to be the cause of the patient’s emergency department visit can be referred to a surgeon for an outpatient workup. Instructions should be given to return to the emergency department immediately if abdominal, back, or flank pain develops.

Pearls and Pitfalls

  • A ruptured AAA should be in the differential diagnosis for any patient older than 50 years with abdominal, back, or flank pain.
  • In a patient with an AAA who develops acute pain, assume rupture is imminent or has already occurred.
  • The patient with a ruptured AAA who is hemodynamically stable can deteriorate at any time.
  • Patients with ruptured AAA need emergent surgical intervention.
  • Aggressive fluid resuscitation can worsen hemorrhage and should not delay transportation to the operating room.
  • Patients with AAA diagnosed in the emergency department should only be referred for outpatient workup if it is clear that symptoms prompting the visit are unrelated to the aneurysm.

References

  • Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th Edition. Elsevier. Vol. 2:1330-41.