Superior Vena Cava Syndrome

Updated: May 15, 2017
  • Author: Todd A Nickloes, DO, FACOS; Chief Editor: Vincent Lopez Rowe, MD  more...
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Overview

Background

Superior vena cava syndrome (SVCS) is obstruction of blood flow through the superior vena cava (SVC). It is a medical emergency and most often manifests in patients with a malignant disease process within the thorax. A patient with SVCS requires immediate diagnostic evaluation and therapy.

William Hunter first described the syndrome in 1757 in a patient with syphilitic aortic aneurysm. [1]  In 1954, Schechter reviewed 274 well-documented cases of SVCS reported in the literature; 40% of them were due to syphilitic aneurysms or tuberculous mediastinitis. [2]

Since the early reports, these infections have gradually decreased as the primary cause of SVC obstruction. Lung cancer, particularly adenocarcinoma, is now the underlying process in approximately 70% of patients with SVCS. [3, 4, 5] However, as many as 40% of cases are attributable to nonmalignant causes. [1]

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Pathophysiology

The SVC is the major drainage vessel for venous blood from the head, neck, upper extremities, and upper thorax. 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. It is a thin-walled, low-pressure, vascular structure. This wall is easily compressed as it traverses the right side of the mediastinum. [6]

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. [4]

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 H2O has been recorded in patients with severe SVCS.

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Etiology

More than 80% of cases of SVCS are caused by malignant mediastinal tumors. [7, 8, 9] Bronchogenic carcinomas account for 75-80% of all these cases, with most of these being small-cell carcinomas. [3] Non-Hodgkin lymphoma (especially the large-cell type) account for 10-15%. Causes of SVCS appear similar to the relative incidence of primary lung and mediastinal tumors. Rare malignant diagnoses include Hodgkin disease, metastatic cancers, [10] primary leiomyosarcomas of the mediastinal vessels, and plasmocytomas. [11, 12, 13]

Nonmalignant conditions that can cause SVCS include the following:

These account for approximately 22% of cases of SVCS. [11, 14, 15, 16]

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Epidemiology

United States statistics

SVCS develops in 5-10% of patients with a right-side malignant intrathoracic mass lesion. In 1969, Salsali and Cliffton observed SVCS in 4.2% of 4960 patients with lung cancer; 80% of the tumors inducing SVCS were of the right lung. [17] In five large series of small-cell lung cancer, 9-19% of patients demonstrated SVCS. In 1987, Armstrong and Perez found SVCS in 1.9% of 952 patients with lymphoma. [18]

Age-, sex-, and race-related demographics

Malignant causes of SVCS are predominantly observed in individuals aged 40-60 years. Benign causes account for most of the cases diagnosed in individuals aged 30-40 years. Obstruction of the SVC in the pediatric age group is rare and has a different etiologic spectrum.

Malignant causes of SVCS are most commonly observed in males because of the high incidence of lung cancer in this population. In contrast, cases related to benign causes show no sex-related differences in frequency.

The frequency of SVCS in different races depends largely on the frequency of lung cancer and lymphomas in these populations.

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Prognosis

Survival in patients with SVCS depends mainly on the course of the underlying disease. No mortality, per se, results directly from mild venous congestion.

In patients with benign SVCS, life expectancy is unchanged. If SVCS is secondary to a malignant process, patient survival correlates with tumor histology. Patients with signs and symptoms of laryngeal and cerebral edema have the most life-threatening manifestations of SVCS and are in danger of sudden death.

Clinical observations show that approximately 10% of patients with a bronchogenic carcinoma and 45% of patients with lymphoma treated with irradiation live at least 30 months. In contrast, patients with untreated malignant SVCS survive for only about 30 days. [5]  Survival for those who do not respond to treatment is similar.

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