Superior vena cava obstruction

Synonym: superior vena cava syndrome

What is superior vena cava obstruction?

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. The most common cause is superior mediastinal pressure associated with lung cancer (over 85%).^{1 2}

The SVC extends from the junction of the right and left innominate veins to the right atrium. 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 easily get compressed.

The SVC provides venous drainage for the head, the neck, the upper extremities and the upper thorax. When obstructed, collateral routes are provided by four main pathways:

• The azygous venous system, which includes the azygous vein, the hemizygous 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.

Aetiology³

One American study reviewed the aetiology of 78 patients with SVC obstruction over five years. ⁴ In adults, bronchogenic carcinoma was the most common cause of SVC obstruction. Small-cell carcinoma (22%) and non-small cell carcinoma (24%) comprised the majority of cases, with lymphoma and germ cell tumours responsible for a smaller but significant proportion. Of note, an intravascular device was the most common cause in benign cases, followed by fibrosing mediastinitis.

The incidence of device-related superior vena cava obstruction has been increasing due to modern-day use of catheters, pacemakers, and defibrillators. Clinically silent venous thrombosis can occur in up to 30% of patients with pacer leads. However SVC obstruction is rare and seen in only 0.1% to 3.3% of patients. Lead extraction with subsequent re-implantation also causes mechanical trauma as additional risk factors for venous occlusion.⁵

In children, the most common causes are T-cell acute lymphoblastic leukaemia and non-Hodgkin's lymphoma (T-cell lymphoblastic lymphoma).⁶

How common is SVC obstruction?⁷

Superior vena cava obstruction is a significant disorder affecting up to 10% of small-cell lung cancer patients and 2-4 % of all lung cancer patients. It is otherwise very difficult to provide incidence and prevalence figures because of the large number of possible underlying causes.

SVC obstruction symptoms

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.⁴ 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

Signs may include:¹

• Dilated veins over the arms, neck and anterior chest wall.

• Oedema of the upper body, extremities and face.

• Severe respiratory distress.

• Cyanosis.

• Engorged conjunctiva.

• Convulsions and coma.

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

Investigations

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

Imaging

• CXR: this may reveal a widened mediastinum or a mass on the right side of the chest.

• Doppler scanning: Doppler flows correlate well with CT scanning and changes seen during the respiratory cycle can be used to evaluate the severity of obstruction and the effect of therapy.⁸

• Enhanced CT and MRI scanning: the method of choice for imaging is contrast- enhanced CT with multiple phase imaging, as it has a high sensitivity and specificity and reliably allows to define the underlying pathology. Contrast- enhanced multislice CT is also suitable for the detection of effusions, metastatic intra- and extrapulmonary manifestations, assessment of collateral vasculature and planning of interventional procedures. Contrast-enhanced MRI might be used as an alternative diagnostic tool in case of intolerance to iodine contrast media.⁹

Procedures

Most cases of SVC obstruction present before the primary cause is elucidated, and there has been some controversy as to whether treatment should be instituted before diagnostic procedures are carried out.¹⁰ Radiotherapy, for example, can destroy histologically useful material.¹¹ However, the underlying pathology is usually easy to identify.

Bronchoscopy has a reported diagnostic yield of >70%, whilst mediastinoscopy or mediastinotomy has a yield of >90%. The latter has a high anaesthetic and complication risk; ultrasound-assisted biopsies have been found to be safer with a similar yield.¹²

SVC obstruction treatment

Superior vena cava obstruction may be life-threatening and requires emergency treatment, particularly if laryngeal oedema causing laryngeal constriction, or cerebral oedema is present.⁷

In the past, radiation therapy was considered first-line treatment, particularly in patients with airway obstruction. However, in recent years, endovascular therapy is more frequently used first, or in combination with radiation therapy, to provide rapid relief of clinical symptoms, with reduced complications.^{3 5}

Medical

• Elevation of the head, and oxygen, may help to provide symptomatic relief.

• Corticosteroids and diuretics may be indicated in the emergency situation (eg, reduced cardiac output, cerebral or laryngeal oedema) although evidence for their efficacy is lacking.

• 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 symptoms are rapidly deteriorating or there have been multiple attempts to obtain a tissue diagnosis without success.

• Chemotherapy may be indicated in chemo-sensitive tumours (eg, small-cell lung cancer).

• Anticoagulation may be required in cases where venography has demonstrated central vein thrombosis, to prevent pulmonary embolism. It may also be indicated in central venous stenosis to prevent thrombosis.

Surgical

Benign disease

• Stenting and/or angioplasty (also known as endovascular surgery) are particularly hopeful in patients requiring long-term venous access (eg, haemodialysis, total parenteral nutrition), or severe SVC obstruction symptoms. An increasing body of evidence suggests it should be considered as first-line treatment for all benign disease, as it is as effective but even less invasive than angioplasty.¹³

• Surgical bypass of the obstruction is technically difficult but may be indicated in some cases. There are no large trials comparing this approach with stenting in benign disease.

• Selected patients may benefit from resection of the blockage, and reconstruction.¹⁴

Malignant disease

• Stenting is useful in relieving obstruction and a National Institute for Health and Care Excellence (NICE) review concluded that it was more effective and produced a quicker response than chemotherapy or radiotherapy.² Thrombolysis and angioplasty may also be indicated in individual patients.

• Reconstructive surgery is possible and may be assisted by the use of autologous tissue.¹⁵

• Insertion of a prosthesis does not increase the overall mortality from SVC resection and is a feasible option where reconstructive surgery is not possible.¹⁶

Prognosis

The prognosis for the relief of SVC obstruction is good with radiation therapy or stenting. However, the ultimate prognosis is of course associated with the underlying condition.