Thoracic Outlet Syndrome is a group of disorders that occur when certain blood vessels or nerves are compressed.
Between the rib cage and the collarbone (clavicle) is a space where the main blood vessels and nerves pass from the neck and the chest into the arm.
This space is called the thoracic outlet. From this outlet, the nerves and blood vessels leave the neck between two muscles (scalene muscles).
If pressure is put on the nerves or blood vessels as they go through the thoracic outlet, a cluster of symptoms can occur. (This is called a syndrome.)