Superior vena cava obstruction
Compression, invasion or thrombosis of the superior vena cava blocks venous drainage from the head, neck and arms, raising upstream pressure until collaterals open or the airway is threatened.
Definition
Superior vena cava obstruction is impaired blood flow through the superior vena cava caused by external compression, direct tumour invasion, intraluminal thrombosis or post-treatment stenosis. It is diagnosed clinically from swelling of the face, neck or arms with distended, non-pulsatile neck and anterior chest-wall veins, and confirmed anatomically on contrast-enhanced venous-phase CT of the thorax.
First principles
The pressure has nowhere to go, and speed decides severity
The superior vena cava (SVC) is a thin-walled, low-pressure vessel draining the head, neck, arms and upper chest. Narrowing raises pressure across that whole territory. Slow occlusion lets collateral veins open across the chest wall, so symptoms stay mild. Rapid occlusion gives no time to compensate, and the patient arrives with a swollen face and arms. That is why two people with identical scans can look entirely different.
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