The severity of the syndrome depends on the rapidity of onset of the obstruction and its location. The more rapid the onset, the more severe the symptoms because the collateral veins do not have time to distend to accommodate an increased blood flow. If the obstruction is above the entry of the azygos vein, the syndrome is less pronounced because the azygous venous system can readily distend to accommodate the shunted blood with less venous pressure developing in the head, arms, and upper thorax. If the obstruction is below the entry of the azygos vein, more florid symptoms and signs are seen because the blood must be returned to the heart via the upper abdominal veins and the inferior vena cava, which requires higher venous pressure.
One study suggested that the general recruitment of venous collaterals over time may lead to remission of the syndrome, although the SVC remains obstructed.
Once SVCS is recognized, prompt clinical attention is important. A diagnosis should be established prior to initiating therapy for the following reasons:
- 75% of patients have symptoms and signs for longer than 1 week before seeking medical attention.
- Cancer patients diagnosed with SVCS do not die of the syndrome itself but rather from the extent of their underlying disease.
- 3% to 5% of the patients diagnosed with SVCS do not have cancer.
In the absence of tracheal obstruction, SVCS is unlikely to be a life-threatening oncologic emergency, and treatment prior to definitive diagnosis is not justified.
The initial evaluation of the patient should include a chest radiograph to look for mediastinal masses and associated findings, such as pleural effusion, lobar collapse, or cardiomegaly. Computed tomography (CT) scanning of the thorax yields the most useful diagnostic information and can define the anatomy of the involved mediastinal nodes. Venous patency and the presence of thrombi are assessed by using contrast and rapid scanning techniques. Depending on local expertise, contrast or nuclear venography, magnetic resonance imaging, and ultrasound may be valuable in assessing the site and nature of the obstruction.
If bronchogenic carcinoma is suspected, a sputum specimen should be obtained. If the sputum specimen is negative, a biopsy specimen should be taken from the most accessible site that is clinically involved with disease. The biopsy approach depends on the working diagnosis, the location of the tumor, the physiologic status of the patient, and the expertise available at the facility. It may include bronchoscopy, biopsy of palpable cervical or supraclavicular lymph nodes, needle biopsy of a lung mass or mediastinal nodes using either CT or ultrasound guidance, mediastinoscopy, mediastinotomy, median sternotomy, video-assisted thoracoscopy, and conventional thoracotomy. The biopsy findings will help the clinician plan appropriate treatment.