Imaging description

The presence of air in the abdominal aorta raises the possibility of recent surgery, instrumentation, infection (Figure 72.1) or aortoenteric fistula (AEF) (Figure 72.2).

Imaging features favoring post-surgical air include a fat plane between the aorta and bowel and no tethering of the bowel. The presence of a fat plane essentially rules out AEF (Figure 72.3).

Importance

Air in the abdominal aorta may be a sign of important pathology or may be innocuous. Findings on imaging alone may not distinguish between the two. Specific inquiry should be made of the timing of intervention. Air is not atypical in the first 10 days after intervention.

Infection should be considered in a patient with fever and positive blood culture.

AEF is a surgical emergency and untreated can have a near- certain mortality. AEF can be clinically silent and imaging may provide the life-saving clues.

Typical clinical scenario

The patient is post-open or has a stent graft repair of abdominal aortic aneurysm. CT is obtained for surveillance or symptoms. Patients with AEF fistula may present with hematemesis, melena, sepsis, and abdominal pain. Air may be detected incidentally.

Differential diagnosis

The differential diagnosis for air in the aorta includes infection, aortoduodenal fistula, or instrumentation. Infection may lead to an aortoduodenal fistula and vice versa.

Teaching point

The presence of air in the abdominal aorta is both reflective of serious pathology and an expected finding post-intervention. Imagers should be aware of the bandwidth of possibilities and use findings on imaging and pertinent clinical information.