mediastinum

If the two lungs are the side rooms of the chest, the mediastinum is the central corridor between them. It is the compartment in the middle of the chest, sitting between the lungs and behind the breastbone, where the body packs its most vital plumbing and wiring close together.

Crowded into this space are the heart and the membrane around it, the great vessels carrying blood to and from the heart, the windpipe and main bronchi, the esophagus, the thymus, important nerves, and many lymph nodes. Anatomists divide the mediastinum into compartments — broadly anterior, middle and posterior — because what normally lives in each region predicts what kind of abnormality is likely to arise there.

For the lung doctor, the mediastinum matters in two main ways. Its lymph nodes are key landmarks in staging lung cancer, since spread to them changes treatment and outlook. And masses that grow in it can press on neighboring structures — squeezing the windpipe, the esophagus or the great veins — so locating a problem to a mediastinal compartment is often the first step toward identifying it.