High-attenuation crescent sign

Last revised by Joshua Yap on 25 Jan 2023

The high-attenuation crescent sign, also called the hyperdense crescent sign, represents an acute hematoma within either the mural thrombus or the aneurysm wall, especially when detected on unenhanced CT scans. It is a specific sign of impending abdominal aortic aneurysm (AAA) rupture or so-called contained rupture.


The high attenuation is caused by fresh blood that first insinuates itself into the mural thrombus and later penetrates the aortic wall. Thus, the pathophysiology is not similar to that of an intramural hematoma, in which hemorrhage occurs from within the aortic wall.

As an indicator of AAA complicated by intramural hematoma, contained or uncontained rupture; the high-attenuating crescent sign has been shown to be 77% sensitive, 93% specific, and has a positive predictive value of 53% 1.

Treatment and prognosis

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.

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