Superior vena cava (SVC) syndrome (SVCS) is characterized by gradual, insidious compression/obstruction of the superior vena cava. Although the syndrome can be life threatening, its presentation is often associated with a gradual increase in symptomatology. For this reason, diagnosis is often delayed until significant compression of the superior vena cava has occurred.
Extrinsic compression of the superior vena cava is possible because it has a thin wall coupled with a low intravascular pressure. Because the superior vena cava is surrounded by rigid structures, it is relatively easy to compress. The low intravascular pressure also allows for the possibility of thrombus formation, such as catheter-induced thrombus.
The subsequent obstruction to flow causes an increased venous pressure, which results in interstitial edema and retrograde collateral flow.
Superior vena cava syndrome is chiefly associated with malignancy. Currently, more than 90% of patients with superior vena cava syndrome have an associated malignancy as the cause. This contrasts with studies in the early 1950s in which a large proportion of cases were nonmalignant. Infectious causes (eg, syphilis, tuberculosis) have decreased because of improvements in antibiotic therapy. Of the nonmalignant causes of superior vena cava syndrome, thrombosis from central venous instrumentation (catheter, pacemaker, guidewire) is an increasingly common event, especially as these procedures become more common.
In developing countries, nonmalignant causes of superior vena cava syndrome continue to constitute a significant percentage. Still, superior vena cava syndrome occurs infrequently in the general population.
Bronchogenic carcinoma (CA) accounts for more than 80% of cases of superior vena cava syndrome. Even when treated with radiation, only 10% of these patients are alive 30 months after presentation. However, patients with superior vena cava syndrome due to a malignant cause survive only 30 days without radiation.
Superior vena cava syndrome has no racial predilection. However, because of poorer access to adequate health care, some socioeconomic groups have a disproportionately greater representation.
Because most superior vena cava syndromes are caused by bronchogenic carcinoma, the age distribution is skewed strongly toward elderly persons. Nonmalignant causes, as well as lymphoma, tend to affect younger people more than malignancy-associated superior vena cava syndrome. The age range reported in one study was 18-76 years, with a mean age of 54 years. 
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