High attenuation crescent sign or hyperdense crescent sign is a radiologic sign indicating impending aortic rupture. [1] [2] It is seen as a curvilinear area paralleling the vessel wall of the aorta. [3] The hyperdense area is due to intramural or mural thrombus haemorrhage. The blood that dissects through mural thrombosis or wall of the aneurysm causes weakening of the wall. [4] This is of relatively high density compared to the psoas muscle in contrast-enhanced CT and greater than the aorta in non-contrast CT imaging. [5]