Embryology of the thoracic outlet

The thoracic outlet is the area in the lower neck traversed by the brachial plexus and subclavian vessels between the thorax and axilla. This dynamic space is formed by the first thoracic vertebra, first rib, and manubrium of the sternum. The thoracic outlet changes in volume with the movement of the upper limbs, thorax, and neck, is occupied by scalene and prevertebral muscles and fibrous structures, and is limited by osseous structures-the clavicle, first rib, and cervical vertebrae and their transverse processes. During upper limb abduction, patients with thoracic outlet syndrome (TOS) have been found to decrease the space of the outlet more compared to healthy individuals.