This patient presented with acute abdominal pain and hypotension. His non-contrast CT shows a large AAA and extensive periaortic haematoma. A thick (but subtle) hyperdense crescent is present within the aortic wall posteriorly and laterally which represents acute intramural haematoma, a sign of acute or impending rupture.
A ruptured AAA carries a 60 to 90% mortality before the patient reaches hospital and a 30 to 80% operative mortality for those who make it to surgery. The risk of rupture is proportional to the size and rate of growth of the aneurysm. Aneurysms greater than 5cm diameter or that grow faster than 10mm per year have a significantly increased risk of rupture and are indications for elective operative repair.

1. Dahnert W. Radiology Review Manual, 5th edition. Lippincott, Williams and Wilkins 2003
2. Rakita, D. et al Spectrum of CT Findings in Rupture and Impending Rupture of Abdominal Aortic Aneurysms, Radiographics 2007;27:497-507

Credit: Dr Donna D’Souza