The most common cause of SVCO in the first world is malignancy; historical causes included mediastinal infections. Thrombus is another possibility, particularly if a central line is in situ.
Most cases of SVCO are due to:
- Lung cancer (either small or non small cell)
- Non-Hodgkin's Lymphoma
- Other mediastinal tumours
- Metastatic tumours to the mediastinum
Hodgkin's disease rarely causes SVCO.
Obstruction of the SVC causes blood to be diverted through collateral channels to return to the heart via the azygos or inferior vena cava. This is often readily apparent on CT with contrast.
Patients usually complain of dyspnoea. Swelling of the face or arms is common, as is the feeling of pressure. Rarely, severe cases can present with cerebral oedema (somnolence, headache, nausea and vomiting) or airway obstruction in combination with SVCO; these cases require emergency stenting and radiotherapy whereas most other cases can wait for histological diagnosis.
CXR may be helpful but the investigation of choice is CT with contrast of the chest. This can demonstrate the site of obstruction, degree of obstruction and the presence of collateral vessels - these are virtually pathognomic of SVCO. Venography can help to localise the exact position of the obstruction but is usually only performed in the setting of an endovascular stent placement.
Emergency therapy is only indicated for patients with cerebral oedema and/or airway obstruction. Emergency therapy consists of head elevation, corticosteriods, endovascular stent placement (which causes rapid resolution of pressure) followed by radiotherapy to the mediastinum.
All other cases require histological diagnosis prior to systemic or radiotherapy. Endovascular stenting remains a useful procedure in any setting as it is highly effective (95-100%), has low rates of failure (10%) and does not compromise the diagnosis. Histological diagnosis can be obtained by biopsy, either through mediastinoscopy or percutaneous CT guided biopsy. Core biopsy or excisional biopsy is frequently most useful as a number of the malignancies that cause SVCO require tissue architecture for diagnostic purposes.
Aside from stenting, symptomatic relief can be obtained by:
- Head elevation
- Diuretics (although the evidence for this is not strong)
- Oxygen (to relieve dyspnoea)
Definitive therapy depends on the nature of the obstruction.
- Chemosensitive malignancies (eg. small cell lung cancer, lymphoma, germ cell tumours) should be treated with systemic therapy urgently.
- Chemoresistant malignancies (eg. non small cell lung cancer, breast cancer, thymoma) should be treated with local radiotherapy first followed by chemotherapy
Radiotherapy continues to play a role in the management of SVCO. Typical dose would be 20 Gy in 5 fractions. In some malignancies that are treated with chemoradiotherapy (localised small cell lung cancer, diffuse large B Cell lymphoma) it is essential to avoid radiotherapy if possible to allow for curative doses of treatment to be delivered later.