Diagnosis by computed tomography of arteriovenous fistula complicating ruptured iliac artery aneurysm.

Isolated iliac artery aneurysms comprise less than 1% of all arteriosclerotic aneurysms. Spontaneous iliac arteriovenous fistula is a rare complication of these aneurysms with only 16 cases previously described. The diagnosis depends on a strong clinical suspicion and usually requires angiography for confirmation. We report a case in which CT with contrast medium showed clear findings of a spontaneous iliac arteriovenous fistula complicating rupture of an isolated iliac artery aneurysm. CT findings included: (1) iliac artery aneurysm, (2) vena caval dilatation, (3) rapid flow of contrast medium from the arterial side into the dilated inferior vena cava on dynamic scanning, (4) increased density of the inferior vena cava similar to that of the aorta caused by entry through the fistula of blood with a high concentration of iodinated contrast medium, and (5) the actual fistula connecting the two vessels.