The superior vena cava carries blood from the head, arms and upper trunk to the heart, and approximately one-third of the venous return to the heart. SVCO is caused by intrinsic or extrinsic compression of the superior vena cava.

The most common cause of extrinsic compression is an underlying malignancy. Lung cancer accounts for about 80 per cent of cases. These tend to be right upper lobe tumours or anterior mediastinal masses that compress the vessel wall.

Less common causes of extrinsic compression include lymphoma, testicular cancer, thymoma, mesothelioma, and metastatic disease (most commonly from breast cancer). More rarely, it can be associated with benign conditions, such as tuberculosis, and in the past was seen in patients with syphilis.

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Intrinsic compression can be caused by thrombosis, often related to central venous instrumentation, such as catheters, pacemakers or guide wires.1 When the superior vena cava is obstructed, blood flows through collateral veins, the inferior vena cava or the azygos vein, leading to raised venous pressure and oedema. The severity of symptoms depends on the site and degree of narrowing of the superior vena cava and the speed of onset of the compression.

The underlying diagnosis influences prognosis. SVCO secondary to lung cancer is generally associated with a poor prognosis, with a median survival of six months. Lymphomas and testicular tumours with SVCO are potentially curable.

Clinical features
SVCO can occur in patients with an existing diagnosis of malignancy, but can also be the presenting symptom in previously undiagnosed patients. Symptoms are usually gradual in onset as the tumour increases in size, although it can develop rapidly over weeks or even days, especially if related to a thrombotic event.

Patients may complain of breathlessness, facial swelling, and redness in the face. Their neck, arms, or hands may become swollen and they can complain of a headache and dizziness which is worse when leaning forward or bending over. Patients may also develop oedema around the larynx or pharynx and this can cause cough, hoarseness, dyspnoea, stridor, and dysphagia. These symptoms may also be due to the underlying malignancy. Rarely, cerebral oedema can develop and this may result in confusion or coma. The main symptoms are listed in Box 1.

Examination often reveals a raised JVP, visibly distended venous collaterals on the chest wall, oedema of the arm and plethora of the face. Patients may have signs of underlying malignancy, such as clubbing or Horner’s syndrome. It is important to examine for evidence of lymphadenopathy and to consider a breast examination if metastatic disease is suspected.

SVCO is rarely an acute emergency unless there is associated airway obstruction and stridor. The diagnosis is usually made clinically and the history and examination should guide the physician towards an underlying cause. The severity of symptoms also helps to guide management.

A chest X-ray may show a widened mediastinum or primary lung lesion (Figure 1). The most useful imaging technique is a CT scan of the chest (Figure 2), especially if IV contrast is used. This allows visualisation of the superior vena cava and gives details about the site and the possible cause of the obstruction. CT scans may also provide staging information about the underlying tumour. MRI may be used in patients who have had a previous allergy to contrast.

Patients without a confirmed underlying diagnosis should have tissue obtained for a histological diagnosis, because management will vary according to the underlying pathology. Palpable peripheral lymph nodes may be easier to biopsy than a mediastinal mass. If there are no peripheral nodes to biopsy, patients may require CT-guided biopsy, bronchoscopy, or sometimes mediastinoscopy to obtain a diagnosis. Discussing cases at hospital multidisciplinary meetings is advised, but this should not delay diagnosis.