SVC Obstruction

Synonym:Superior Vena Cava Syndrome

Obstruction of the superior vena cava (SVC) can be due to external pressure, involvement of the vessel by tumour tissue, or a blood clot obstructing the lumen. William Hunter first identified the condition in 1757 in a patient with syphilitic aortic aneurysm.¹ Today, the commonest cause is superior mediastinal pressure associated with lung cancer.²

The SVC extends from the junction of the right and left innominate veins to the right atrium.³ It is surrounded by the sternum, trachea, right bronchus, aorta, pulmonary artery, and the perihilar and paratracheal lymph nodes. All these are relatively rigid structures, and as the SVC runs along the right side of the mediastinum this thin-walled low pressure vessel can get easily compressed. The SVC supplies venous drainage for the head, the neck, the upper extremities, and the upper thorax. When obstructed, collateral routes are provided by four main pathways:^4,5

• The azygous venous system, which includes the azygous vein, the hemiazygous vein, and the connecting intercostal veins
• The internal mammary venous system plus tributaries and secondary communications to the superior and inferior epigastric veins
• The long thoracic venous system connection to the femoral veins
• The long thoracic venous system connection to the vertebral veins

• Primary bronchial carcinoma
• Lymphadenopathy due to lymphoma
• Constrictive pericarditis
• Chronic fibrotic mediastinitis
• Clot associated with indwelling catheter or pacemaker wires
• Thymoma
• Localised infection
• Thyroid cancer
• Synovial cell carcinoma
• Teratoma
• Retrosternal goitre
• Mediastinal fibrosis
• Thoracic aortic aneurysm
• Aortic aneurysm
• Angiosarcoma

In children the commonest causes are:

• T-cell acute lymphoblastic leukemia
• Non-Hodgkin's lymphoma (T-cell lymphoblastic lymphoma)⁶

American studies indicate that SVC obstruction develops in 5-10% of patients with a right-sided malignant intrathoracic mass lesion.⁴ One study of small-cell lung cancer patients found SVC obstruction in 87 patients out of 724 at the time of diagnosis.⁷ With increasing cardiovascular interventions, the incidence of benign causes is increasing. One study found that an intravascular device was the most common etiology in benign cases (22 of 31 cases), with fibrosing mediastinitis the second most common benign etiology (6 cases).⁸

Gender predilection reflects aetiology, with more males than females due to the prevalence of lung cancer. Malignant causes are commoner in the 40-60 age group, and benign causes in the 30-40 age group.⁴

History

The onset may be gradual or acute, depending on how quickly the condition proceeds from partial to complete obstruction, and the degree of development of a collateral circulation.

One study identified dyspnoea, cough and chest pain at rest as being the most prominent symptoms, particularly in patients with malignancy.⁸ Other symptoms can include neck and face swelling, arm swelling, dizziness, headache, disturbed vision, nausea, nasal stuffiness, stupor and syncope. Symptoms tend to be aggravated by postures which increase the venous pressure in the upper part of the body such as bending over or lying down.

Examination^4,2

Signs may include:

• Dilated veins over the arms, neck and anterior chest wall
• Dilated veins over the abdomen if a collateral circulation has developed
• Oedema of the face and arms
• Stridor due to laryngeal oedema
• Reduced mental function due to cerebral oedema
• Congested veins of the anterior chest wall and flushed face
• Cyanosis
• Papilloedema
• Stupor and even coma

Signs may get more pronounced when the arms are lifted above the head.

Diagnosis may be made on clinical grounds in patients with overt symptoms and signs. However, in more subtle cases, further investigations are required.

Imaging

• Chest X-ray This may reveal a widened mediastinum or a mass on the right side of the chest.
• CT scanning This shows more detail, particularly of surrounding structures such as the bronchi and vocal cords, and may be necessary to guide more invasive investigative procedures . Various refinements including the use of several detectors taking images in different planes. Injection of contrast media to highlight collateral circulation improves the sensitivity of CT scanning even further.^9,10
• MRI This was thought to have some advantages, but these have largely been cancelled out by the technological enhancement of CT. MRI also takes longer and is more expensive.^4,11
• Invasive contrast venography This is useful in some cases, particularly prior to surgery.

Procedures

• Sputum cytology and biopsy of palpable supraclavicular node may be helpful in establishing a diagnosis of malignancy.
• Anterior mediastinotomy or cervical mediastinoscopy are useful in cases where malignancy cannot be excluded by other means.¹²

Medical⁴

• Elevation of the head and oxygen may help to provide symptomatic relief.
• Corticosteroids and diuretics may be indicated in the emergency situation (e.g. reduced cardiac output, cerebral or laryngeal oedema).
• Radiotherapy is indicated in some lung cancer cases. The use of radiotherapy in SVC obstruction before a diagnosis of malignancy has been established is controversial, but may occasionally be justified if the clinical situation is deteriorating.
• Chemotherapy may be indicated in chemosensitive tumours (e.g.small-cell lung cancer).
• Anticoagulation will be required in cases where venography has demonstrated central vein thrombosis, to prevent pulmonary embolism. It is also indicated in central venous stenosis to prevent thrombosis.

Surgical¹³

Benign Disease

• Stenting and/or angioplasty may be required in patients requiring long-term venous access (e.g. haemodialysis, total parental nutrition), or severe SVC obstruction symptoms,
• Surgical bypass of the obstruction is technically difficult but may be indicated in some cases. There are no large trials comparing this approach to stenting in benign disease.

This depends on the underlying condition. The average survival rate of untreated patients and those not responding to treatment is thirty days.