Assessment of major venous anomalies by computerized tomography. Congenital anomalies of major venous structures are not common but their identification and relative position, particularly in relation to an abdominal aortic aneurysm, are of significant value in planning and conducting aortic operations. Computed tomography (CT) has become a common method of preoperative evaluation of aortic disease. Its reliability in providing accurate information regarding aneurysmal size, configuration, and extension, as well as the presence of intraluminal thrombus and involvement of the renal and iliac arteries, has been demonstrated. Simultaneous visualization of the major adjacent venous structures with the use of contrast enhancement is obtained, but anatomic variants can be overlooked because they are commonly subtle and considered incidental. The preoperative diagnosis of these venous abnormalities is significant to the vascular surgeon. Such information can be accurately and reliably acquired with the present CT techniques without the need for further diagnostic studies. 