Spectrum of CT findings in rupture and impending rupture of abdominal aortic aneurysms.

Prompt diagnosis of rupture and impending rupture of abdominal aortic aneurysms is imperative. The computed tomographic (CT) findings of ruptured abdominal aortic aneurysms are often straightforward. Most ruptures are manifested as a retroperitoneal hematoma accompanied by an abdominal aortic aneurysm. Periaortic blood may extend into the perirenal space, the pararenal space, or both. Intraperitoneal extravasation may be an immediate or a delayed finding. Discontinuity of the aortic wall or a focal gap in otherwise continuous circumferential wall calcifications may point to the location of a rupture. There usually is a delay of several hours between the initial intramural hemorrhage and frank extravasation into the periaortic soft tissues. Contained or impending ruptures are more difficult to identify. A small amount of periaortic blood may be confused with the duodenum, perianeurysmal fibrosis, or adenopathy. Imaging features suggestive of instability or impending rupture include increased aneurysm size, a low thrombus-to-lumen ratio, and hemorrhage into a mural thrombus. A peripheral crescent-shaped area of hyperattenuation within an abdominal aortic aneurysm represents an acute intramural hemorrhage and is another CT sign of impending rupture. Draping of the posterior aspect of an aneurysmal aorta over the vertebrae is associated with a contained rupture.