Superior vena cava syndrome

Superior vena cava syndrome occurs when blood flow through the superior vena cava is obstructed either from within due to a blood clot or from external compression.

The superior vena cava is a short and wide vein on the right side of the chest that drains blood from the head, upper body and both arms, and delivers all of that blood to the right atrium of the heart.

The superior vena cava can get obstructed a few different ways, and the most common way is via a nearby tumor, through mass effect, where inflammation and swelling pushes up against the superior vena cava.

Alternatively, though, there can be direct tumor invasion into the superior vena cava which is when tumor cells penetrate and grow directly into the superior vena cava. But this is only possible if the tumor is located on the right side near the superior vena cava.

The most common type of cancer that does this is a lung cancer, and when it’s located in the apex of the right lung near the superior vena cava, it’s given the name Pancoast tumor - after Dr. Henry Pancoast who first described them.

Also in that area, though, you’ve got a bunch of lymph nodes, and another possible cause of SVC syndrome a tumor of the lymph nodes, which would could lead to compression of the SVC.

This could be lymphomas – or primary cancers of the lymph node - cause superior vena cava syndrome, or secondary and have spread from somewhere else, like the lungs.

Apart from tumors, the superior vena cava can also get obstructed if a blood clot or thrombosis forms within it. This most often develops in individuals who have a long-term device like an indwelling central venous catheter.

Regardless of the cause, when the superior vena cava gets obstructed, behind the obstruction you’ll get an increase in venous pressure.

When this happens, blood starts to get re-routed through different blood vessels, essentially draining into the inferior vena cava, which also drains into the right atrium.

These are now called collateral blood vessels, and are essentially alternate routes.

If the blockage is low enough, it could be through the azygos system, but also other options are the internal mammary, lateral thoracic, and esophageal venous systems.