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High-attenuation crescent sign

Dr Yuranga Weerakkody and Dr Erik Ranschaert et al.

The high attenuating crescent represents an acute haematoma or bleed within either the mural thrombus or the aneurysmal wall, especially when detected on unenhanced CT-scans. It is a specific sign of impending AAA rupture or so-called contained rupture.

The hyperattenuation is caused by fresh blood that first insinuates itself into the mural thrombus and later penetrates the aortic wall. Thus, the pathophysiology is dissimilar to that of an intramural haematoma, in which haemorrhage occurs from within the aortic wall.

Sensitivity of the high-attenuating crescent sign as an indication of complicated aneurysm is 77%; specificity, 93%; and positive predictive value of 53%.

When seeing this sign in an aneurysm, especially in patients with pain, it is warranted to inform the referring physician or surgeon about the high risk for aneurysmal rupture, even if there are no primary or frank signs of leakage. This condition may require emergent surgical management and warrants close vitals monitoring.