RADIOLOGY: AORTA: Case# 28: LEAKING AAA. 85 year old female who has a known abdominal aortic aneurysm nowpresents with blood per rectum. The aortic aneurysm measures 7.2 x 7.2 cm (previously measured 5.2 x 6.0 cm). There are curvilinear calcifications internally. The lateral aneurysm contour is markedly lobular particularly posteriorly. Numerous punctate foci of increased density within the antero-lateral thrombosed lumen are consistent with enhancement of dissection planes. The aneurysmal mass displaces the distal third duodenal segment anteriorly. There is a focus of increased density noted just posterior to the duodenum. Abdominal aortic aneurysms usually occur in the setting of atherosclerotic disease but may be caused by syphilis, by extension of a dissection from above, or by connective tissue disorders such as Takayasus arteritis. Complications of abdominal aortic aneurysm include rupture, peripheral embolization, thrombosis, and infection. The incidence of rupture increases with increasing aneurysm size above 4 cm. Rupture usually occurs into the left retroperitoneal space and rarely into the gastrointestinal tract and inferior vena cava. If a ruptured or leaking aneurysm is suspected, CT should be done with contrast enhancement. Typical findings include obscuration or anterior displacement of the aneurysm by an irregular high density mass or collection that extends into one or both perirenal spaces. The wall of the aneurysm may be identified by calcifications while the lumen enhances. Other findings include anterior displacement of the kidney by hematoma, enlargement or obscuration of the psoas muscle, and a focally indistinct aortic margin that corresponds to the site of rupture. In contrast, a chronic pseudoaneurysm appears as a well-defined, ususally round mass with attenuation similar or lower than that of the native aorta on noncontrasted images.