Thoracic outlet syndrome (TOS) is a group of disorders characterized by paresthesias, pain and weakness of the upper extremities due to compression, tension or inflammation of the neurovascular bundle as it passes through the thoracic outlet. There are 3 forms of TOS with different clinical pictures and etiologies: neurogenic TOS (NTOS) that can be divided into true or disputed forms, arterial TOS (ATOS) and venous TOS (VTOS) (see these terms).