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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.