RADIOLOGY: AORTA: Case# 21: LEAKING AAA. 70 year old female ultrasound examination documenting a large abdominal aortic aneurysm. A large abdominal aortic aneurysm begins about the level of the renal arteries. It is approximately 7.0 x 7.0 cm in its greatest dimension which is just above the aortic bifurcation. There is a large amount of intramural thrombus as well as calcification within the walls. There is a large amount of soft tissue within the retroperitoneum consistent with hematoma. At the level of the aortic bifurcation at approximately 3 oclock, there is active arterial extravasation from the aortic aneurysm. 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 4cm. Rupture usually occurs into the left retroperitoneal space and rarely into the gastrointestinal tract or inferior vena cava. If a ruptured or leaking aneurysm is suspected, a CT scan of the abdomen 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.