High-attenuating crescent in abdominal aortic aneurysm wall at CT: a sign of acute or impending rupture.

PURPOSE: To determine whether a peripheral high-attenuating crescent in an abdominal aortic aneurysm (AAA) on unenhanced computed tomographic (CT) scans is a sign of impending or active aneurysm rupture. MATERIALS AND METHODS: CT scans were reviewed of 149 consecutive patients operated on because of AAA who had undergone preoperative unenhanced CT scanning. The presence of a peripheral high-attenuating crescent on CT scans was correlated with surgical findings of aneurysm complication. Aneurysm diameter was correlated with presence or absence of pain at the time of CT, high-attenuating crescent, and aneurysm complication. RESULTS: Sensitivity of the high-attenuating crescent sign as an indication of complicated aneurysm was 77%; specificity, 93%; and positive predictive value, 53%. The sign showed a statistically significant correlation with large aneurysm size (P < .001) and presence of pain at the time of CT (P < .003). CONCLUSION: In patients without CT evidence of frank aneurysm leak, the high-attenuating crescent sign should be regarded as a sign of impending AAA rupture, particularly in patients with pain.