Computed tomography of the superior vena cava.

The superior vena cava (SVC) can be visualized and reliably evaluated by computed tomography (CT). Opacification of this vessel with iodinated contrast material and multiplanar reformations can provide information concerning the patency of the lumen and the relationship of the SVC with adjacent mediastinal and lung structures, both normal and abnormal. SVC obstruction leading to SVC syndrome is the most common condition affecting this vessel. It can be caused by both extrinsic compression and intraluminal thrombosis. Numerous collateral pathways have been described by conventional radiographic and anatomic studies with the azygos vein being the most important collateral vessel. From this aspect, five distinct grades of SVC obstruction can be identified. Grade 0: SVC narrowing without clinical evidence of SVC syndrome. Grade I: Moderate SVC narrowing without collaterals. Grade II: Severe SVC narrowing with the azygos vein serving as partial collateral. Grade III: SVC obstruction above the azygos arch. Grade IV: SVC obstruction at or below the level of the azygos arch. Patients with Grades I to IV have clinical evidence of SVC syndrome, and the CT grading roughly corresponds to the severity of clinical findings. CT accurately depicts both the site of SVC obstruction and important collateral pathways and clearly distinguishes between SVC thrombosis and external compression. In this regard, it provides unique information not available from other modalities such as conventional or radioisotope venography. Furthermore, in a number of patients with suspected SVC obstruction, this vessel may be patented, leading to clinical reassessment. The only disadvantage of CT as compared with radionuclide flow studies is the potential hazard from i.v. administration of iodinated contrast material. Less common abnormalities of the SVC include congenital or developmental conditions, such as persistent left SVC, aneurysms, dilation of the vessel due to heart failure, and variations (usually tortuosity) of the thoracic inlet vessels. We conclude that CT should be used as the procedure of choice for the diagnosis of SVC abnormalities, especially in patients with suspected SVC syndrome.