The superior vena cava (SVC) is formed by the confluence of the right and left innominate veins and enters the right atrium at its upper pole. The SVC lies along the right sternal border. The right innominate vein lies more vertical and is shorter then the left innominate vein. The SVC is about 7 cm long. This vein is valveless and is joined by the azygous vein entering the SVC posteriorly.¹ Early in development, two paired anterior cardinal veins form the primitive venous return as the left anterior vein involutes and contributes to the left brachiocephalic vein. The junction of the primitive left anterior cardinal vein (LACV) and the right anterior cardinal vein thus forms the SVC. The primitive cardinal veins coalesce to the atrium via the sinus venosus. The sinus venosus then becomes the coronary sinus (Figure 19-1).

Failure of the left anterior vein to involute is present about 0.3% in the general population but approaches 5% in those with congenital heart disease.² The persistent left SVC empties to the coronary sinus in 90% and to the left atrium 10%. This seemingly tedious embryologic sequence has profound clinical impact in consideration of the persistent left SVC or duplicated SVC. In the case of persistent left SVC connecting to the left atrium, this imposes the risk of right-to-left shunt of air or emboli causing potentially stroke or other systemic embolization. Analogous to the supracardiac subset of total anomalous pulmonary venous connection, a persistent LACV that communicated with the left atrium provides a connection between systemic and pulmonary venous systems. When the persistent left SVC connects to the coronary sinus, any catheter-based venous access may inadvertently the coronary sinus, resulting in cardiac tamponade. Isolated LACV can be treated with ligation. In addition to contrast-enhanced cross-sectional imaging and venography, diagnosis may also be confirmed echocardiographically by coronary sinus dilatation and passage of contrast into it from a left arm vein¹ (Figure 19-2). The coronary sinus is a frequent conduit for placement of a pacemaker lead in a coronary vein. The incidence of coronary sinus dissection with pacemaker lead insertion is about 6%, but perforation or cardiac tamponade is rare.³ A single left-sided SVC is quite rare and may be confused with partial anomalous pulmonary venous return. Another venous anomaly that can be confused for left-sided SVC is a hemiazygous vein draining into the left brachiocephalic vein.

SVC syndrome (SVCS) occurs when blood return through it is obstructed. This condition was first described in the medical literature in 1757 by William Hunter⁴ (Figure 19-3). This case was secondary to thoracic aortic aneurysm. Since Hunter’s description, this disease has undergone several evolutions in its etiology with iatrogenic causes increasing in recent years. The resulting constellation of signs and symptoms being related to poor venous return from the upper body is characteristic. The rapidity of compression dictates the severity of symptoms and the effectiveness of collateral venous flow. The diagnosis of SVCS remains primarily clinical with imaging for confirmation. The SVCS was formerly considered a medical emergency with limited treatment options. In recent years, the ability to effectively treat SCVS has improved with more effective and less invasive treatment options available. Contemporary therapy provides promising outcomes for patients with both benign and malignant causes of SVCS.

Etiology

A review of the literature from 1757 to 1949 by McIntyre and Skyes⁵ of 502 cases of SVCS reported primary malignant tumors as the cause in 33.3% of patients, aortic aneurysm in 30%, and fibrosing mediastinitis in 15.4%. Banker and Maddison⁵ reported 438 cases from 1951 to 1966 with primary malignant tumors accounting for 76%, fibrosing mediastinitis for 9%, and aortic aneurysm for 4%. Malignancy remains the most common cause of SVCS, accounting for approximately 60% to 85% of cases^6,7 (Table 19-1) Non–small cell lung cancer (NSCLC), small cell lung cancer (SCLC), and lymphoma comprise 50%, 22%, and 12% of these, respectively.⁸ Approximately 4% of patients with lung cancer will experience SVCS, with a higher percentage among SCLC.⁷ Up to 10% of patients with SCLC develop SVCS.⁷ Other malignancies are reported with germ cell tumor, thymoma, and metastatic disease (most commonly breast cancer) being described.⁸

Benign disease comprises the remaining 15% to 40% causes of SVCS.⁷ The most common benign cause has previously been attributed to fibrosing mediastinitis. Fibrosing mediastinitis is commonly associated with an excessive inflammatory reaction to histoplasmosis.⁹ Other infectious agents, such as tuberculosis, have also been implicated. Proliferation of fibrotic tissue and local inflammatory process account for symptoms such as SCVS and airway stenosis.⁹ Several recent series have shown stenosis secondary to indwelling catheters or pacemaker wires to be the most common benign cause.^7,10 These may cause up to 75% of benign SVCS.¹⁰ There has been an increase in the prevalence of invasive devices in the central veins secondary to cardiac pacemaker and hemodialysis catheter use.⁷ More than 5 million central venous catheters and about 170,000 cardiac pacemakers are implanted annually in the United States.¹⁰ The incidence of SVC stenosis or thrombosis ranges from 5 % to 42% when a catheter is in the SVC, and the estimated rate of occurrence ranges from 0.003% to 0.2% for each day the catheter remains in place.⁷ The frank syndrome occurs in approximately 1% to 3% of those with a central venous catheter or pacemaker.¹⁰ The risk of central vein stenosis and thrombosis also increases with repetitive placements in a dose-dependent fashion.⁶ Female gender appears to pose a higher risk for catheter-associated venous stenosis.⁶ The prevalence of subclinical SVC stenosis from indwelling catheters is underappreciated and urges judicious use of such devices. Reported rates of mild to moderate stenosis after central vein cannulation are 18% to 50% with higher rates in the subclavian vein compared with internal jugular vein access.⁶ These risks are increased in patients with thrombophilia. Conditions such as factor V Leiden deficiency increase the risk of venous thrombosis. Infectious causes, such as adenopathy from tuberculosis, syphilitic aortic aneurysm, and vessel fibrosis from radiation therapy, also contribute to benign causes. Although malignancy remains the most common cause of SVCS, it is clear that the prevalence of benign causes is increasing, primarily because of increased use of invasive devices.

Presentation

Symptoms vary based on the cause of the obstruction or stenosis. Common symptoms are given in Table 19-2. The normal central venous pressure ranges from 2 to 8 mm Hg and with obstruction of the SVC may increase up to 20 to 40 mm Hg.⁸ The diagnosis of SVCS is largely clinical, and the symptoms are characteristic. With benign disease, or slower onset, formation of collaterals can prevent severe symptoms. Five main venous collaterals allow return to the heart—the azygous, internal mammary, lateral thoracic, vertebral, and portal vein from the esophageal veins via the left gastric vein.⁵ Early signs include dilatation of the upper thorax, arms, and head veins as well as upper body edema. Early symptoms include cough, dyspnea, and occasionally chest pain or dysphagia.¹¹ With rapid invasion or malignant obstruction of the SVC, a more dramatic presentation occurs with the frank syndrome. With rapid compression, prominent venous dilatation and edema occur with laryngeal edema and possible mental status changes from cerebral edema caused by venous congestion cephalad to the occlusion. Visual changes may occur both from cerebral edema as well as corneal edema¹¹(Figure 19-4).Although these severe symptoms have been described and previously was the basis for the classification of SVCS as a “medical emergency,” a review of 1986 patients with SVCS revealed only one death directly attributed to SVC occlusion.⁸ Patients with malignancy are more likely to present with cough, dyspnea at rest, and shoulder pain.⁷ It is possible to have cyanosis as a presenting sign of SVCS in the setting of anomalous venous pathway whereby systemic decompression is via the left atrium, also known as the levoatrial cardinal vein. This rare congenital anomaly connects the pulmonary veins to a remnant of the cardinal veins.¹²