21st June 2023

Aetiology

Malignant SVCO can arise from a number of different mechanisms. These include extrinsic compression from an adjacent tumour, whether from a primary lung/mediastinal tumour or from locoregional lymphadenopathy. There can also be direct invasion into the superior vena cava from adjacent malignancy and obstruction secondary to malignancy-associated thrombosis or embolism.

The most common malignancies associated with SVCO are lung cancers, particularly small cell carcinoma (found in 10% of these patients) as well as non-small cell lung cancer (2-4% of these patients). Typically, tumours sited in the right upper lobe pose the greatest risk due to their anatomical location. Lymphomas are also a common cause, in particular diffuse large B-cell lymphoma (DLBCL) and primary mediastinal large B-cell lymphoma. Other malignancies of the mediastinum including thymoma, thymic carcinoma, germ-cell tumours and mesothelioma contribute to the remaining causes.

The archetypal presenting symptoms include upper limb, neck and facial swelling, dyspnoea, and chest discomfort. These symptoms may be further aggravated by leaning forward. Persistent swelling can lead to oedema of the larynx, leading to stridor and dysphagia. Furthermore, patients can develop cerebral oedema leading to headaches, confusion, and brainstem herniation. Thankfully, due to the greater availability of early imaging, these severe sequelae (airway compromise and cerebral oedema) are becoming increasingly rare. Depending on the underlying tumour biology, the development of SVCO tends to be gradual, which typically allows for the patient to develop venous collaterals, allowing the patient to compensate.

Most patients will have an abnormal chest x-ray. Further imaging in the haemodynamically stable patient is with cross-sectional imaging i.e. CT thorax or MRI (particularly in the case of a ‘Pancoast’ tumour). Duplex ultrasonography can be useful in determining the coexistence of thrombus. Dedicated venography (CT/MRI) may have an application in the planning of endovenous recanalisation. In those patients without a tissue diagnosis, it is imperative that this is sought, and this may be done concurrently with initial management.