Uperior vena cava syndrome (svcs) was first described in l757 in a patient with a syphilitic

ANATOMY OF THE SUPERIOR VENA CAVA

The superior vena cava is a thin-walled, readily com-

pressible vessel that transmits blood to the heart at low

pressure. The superior vena cava is located in the mid-

dle mediastinum and is encircled by rigid structures,

including the trachea, right bronchus, aorta, thymus,

and pulmonary artery. The superior vena cava extends

approximately 8 cm from the innominate vein to the

right atrium. The distal 2 cm of the superior vena cava

are within the pericardial sac. The azygous vein enters

the superior vena cava posteriorly and is a significant

venous collateral channel. Encircling the superior vena

cava are subcarinal, perihilar, and paratracheal lymph

nodes. These nodes drain the right lung and the lower

lobe of the left lung.

2 – 4

PATHOPHYSIOLOGY

Any pathology of the previously noted structures

produces external pressure on the superior vena cava

or internally obstructs the vessel as a result of either

thrombosis or direct invasion by the disease process. In

addition, enlargement of the lymph nodes may also

compress the superior vena cava. In most cases, extrin-

sic compression develops gradually and the symptoms

are initially mild because collateral circulation has suffi-

ciently developed. If the obstruction develops sudden-

ly, as in the case of a malignancy, the collateral circula-

tion has not developed and the patient rapidly be-

comes symptomatic. Thrombosis of the superior vena

cava may progress to involve all the major collateral

vessels, and the resulting thrombosis eventually under-

goes fibrosis that results in permanent occlusion of the

superior vena cava. In this case, thrombolytic therapy is

of little or no benefit unless the treatment is directed at

the primary cause of SVCS.