Inability to show clot: one limitation of ultrasonography of the abdominal aorta.

Ultrasonography is accurate for diagnosis of abdominal aneurysms and clots within them. However, due to technical factors, occlusive clots within the aorta can be missed even at high gain. The authors report three cases in which total occlusion of the abdominal aorta was misdiagnosed as a free lumen occupied by a small clot. An explanation for the shortcomings of ultrasound is offered.