Superior vena cava syndrome

ALSO KNOWN AS: Superior vena cava (SVC) obstruction, super vena cava occlusion

RELATED CONDITIONS: Fibrosing mediastinitis, lung cancer

DEFINITION: Superior vena cava syndrome is characterized by swelling of the face, neck, and arms that results from obstruction or compression of the superior vena cava (the vein connecting the upper half of the body and right atrium of the heart, formed by brachiocephalic veins) from any number of causes, including malignancy, infection, or an iatrogenic cause (inadvertently caused during treatment). Superior vena cava syndrome may also cause difficulty breathing, cough, and hoarseness.

Risk factors: The most common cancers that cause superior vena cava syndrome are non-small cell lung cancer, small cell lung cancer, and non-Hodgkin lymphoma, which together account for about 95 percent of malignant causes of superior vena cava syndrome. Less common malignant causes include mediastinal germ cell tumors, thymoma, metastatic disease, mesothelioma, anaplastic thyroid cancer, and Hodgkin lymphoma. Nonmalignant causes include fibrosing mediastinitis due to histoplasmosis, tuberculosis, or blastomycosis. This syndrome can also be caused by idiopathic fibrosing mediastinitis. Central venous catheters are the most common iatrogenic cause, followed by pacemaker leads, central venous devices, and implantable defibrillators.

Etiology and the disease process: When the superior vena cava is obstructed, there is an increase in venous pressure to between 20 and 40 millimeters of mercury (mmHg), which is diagnostic. In about 40 percent of patients, the obstruction occurs above the azygous vein and is responsible for the most disabling symptoms. Obstruction between the azygous vein and the right atrium is less serious, as the azygous vein can provide collateral venous decompression.

Incidence: Although superior vena cava syndrome is considered a rare disease, affecting less than 15,000 people in the United States each year, it is a well-described complication of both device implantation and central venous catheter placement. Most diagnoses of malignant causes of SVCS occur in individuals between forty and sixty. Because of the high incidence of lung cancer in males, they also experience a higher incidence of SVCS.

Symptoms: The symptoms of superior vena cava syndrome vary depending on the degree of increase in venous pressure, the level of obstruction, the rate at which it develops, and the cause. If extrinsic compression of the superior vena cava is caused by a benign process, such as fibrosing mediastinitis, the obstruction is gradual, allowing time for collateral circulation to develop, and therefore the symptoms are milder. With mild obstruction, symptoms include headache, puffiness of the face, and swelling of the eyelids or neck. Patients quickly find that severity is related to posture, with symptoms often worsening when they lie down or bend over.

If the superior vena cava is invaded or thrombosis occurs, the obstruction develops rapidly, and the symptoms are more acute. If an acute obstruction occurs because of bleeding into a rapidly growing neoplasm, cerebral edema, blurring vision, and drowsiness occur. As the majority of cases are caused by rapidly growing lung cancer, pulmonary symptoms such as shortness of breath, orthopnea, cough, hemoptysis, and chest pain predominate. Other symptoms include hoarseness, stridor, and laryngeal edema from laryngeal obstruction.

Diagnosis: Superior vena cava syndrome was previously diagnosed by upper extremity venography, but with the advent of contrast computed tomography (CT), these scans became the most common modality of diagnosis. CT scans show the extent of the obstruction and its likely cause—a distinct advantage over venography. Direct CT signs of superior vena cava obstruction include nonopacification of the superior vena cava with or without intraluminal filling defects or encasement or extrinsic compression of the superior vena cava by the tumor. Indirect signs of superior vena cava obstruction include opacification of venous collateral circulation. The five major routes of collateral circulation include internal mammary veins, azygous or hemizygous veins, paravertebral veins or Batson venous plexus, anterior jugular veins, and lateral thoracic and thoracoepigastric veins. Additional collaterals include the superior intercostal, parascapular, superficial thoracoabdominal, epigastric, and vertebral veins. The location and extent of the obstruction determine the collaterals that opacify during the contrast CT exam. Sometimes, marked focal enhancement of the liver is seen in cases of superior vena cava obstruction and likely represents low-resistance collateral flow from the superior vena cava through the liver to the inferior vena cava. Magnetic resonance imaging (MRI) is common in patients with contraindications to CT intravenous contrast. However, MRI occasionally fails to differentiate complete and incomplete obstructions because of marked narrowing and slow flow. An advantage of MRI over CT involves clearing up confusion regarding flow-related artifacts seen on CT because of the mixing of opacified and unopacified blood.

Treatment and therapy: Treatment varies with clinical presentations, cause of obstruction, extent of occlusion, and severity of symptoms. Because most cases involve a malignant process that precludes surgical resection, standard therapy includes radiation therapy (often in combination with diuretics and corticosteroids to reduce cerebral edema) and chemotherapy. Some 80 to 90 percent of patients are relieved of superior vena cava syndrome. However, approximately 50 percent of patients relapse, even in benign disease, because, although collaterals develop, thrombosis will continue to propagate and occlude even these collaterals over time. Thrombolytic therapy is used for selected cases of acute thrombosis. Superior vena cava bypass with composite autogenous vein grafts has also been used for patients with benign processes in whom collateral circulation is inadequate to relieve symptoms. Interventions for symptom relief include oxygen as needed, corticosteroids, and diuretics. Intubation or stenting may be necessary if the obstruction is life-threatening (for example, if the airway is compromised).

Prognosis, prevention, and outcomes: With benign causes, symptoms will improve or subside as collateral circulation develops. With malignant causes, an improvement in symptoms varies with the type of tumor involved. However, most patients rapidly improve within a few weeks from the decrease in edema after intensive radiation therapy, steroids, diuretics, and chemotherapy. Death from cancer within the next several months is inevitable, however, with rare survivors beyond two years.

Bibliography

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