Superior Venecaval Syndrome

By Dr Deepu

Definition
History
Pathophysiology
Presentation and Findings
Causes
Diagnostic Workup
Management

Pathophysiology:

The SVC is the major drainage vessel for venous blood from the head, neck, upper extremities, and upper thorax. It is a thin-walled, low-pressure, vascular structure. This wall is easily compressed as it traverses the right side of the mediastinum.

 It is located in the middle mediastinum and is surrounded by relatively rigid structures such as the sternum, trachea, right bronchus, aorta, pulmonary artery, and the perihilar and paratracheal lymph nodes. It extends from the junction of the right and left innominate veins to the right atrium, a distance of 6-8 cm.

Obstruction of the SVC may be caused by neoplastic invasion of the venous wall associated with intravascular thrombosis or, more simply, by extrinsic pressure of a tumor mass against the relatively thin-walled SVC. Complete SVC obstruction is the result of intravascular thrombosis in combination with extrinsic pressure. Incomplete SVC obstruction is more often secondary to extrinsic pressure without thrombosis. Other causes include compression by intravascular arterial devices.

The incidence is on the rise, in line with the increased use of endovascular devices.

An obstructed SVC initiates collateral venous return to the heart from the upper half of the body through four principal pathways. The first and most important pathway is the azygous venous system, which includes the azygos vein, the hemiazygos vein, and the connecting intercostal veins. The second pathway is the internal mammary venous system plus tributaries and secondary communications to the superior and inferior epigastric veins. The long thoracic venous system, with its connections to the femoral veins and vertebral veins, provides the third and fourth collateral routes, respectively.

Despite these collateral pathways, venous pressure is almost always elevated in the upper compartment if obstruction of the SVC is present. Venous pressure as high as 200-500 cm H₂ O has been recorded in patients with severe SVCS.

Presentation