Anatomy - Thoracic outlet syndrome (TOS) - Left transaxillary first rib resection (TFRR) - Vascular surgery

The neurovascular structures (subclavian artery and vein, brachial plexus fascicles) travel through several narrow anatomic spaces in the thoracocervical region: sternocostovertebral space, scalene gap, costoclavicular space, and pectoralis minor (coracopectoral) space. Congenital and acquired changes in the anatomic equilibrium between the various structures can, because of compression or kinking, injure the neurovascular bundle. TOS in women mainly occurs in lean, non-athletic individuals, while in men it affects in particular the muscular, athletic males (e.g., basketball players and bodybuilders).

1. Fibromuscular bands

Congenital atypical fibromuscular bands often predispose to the pathogenesis of TOS. There are 20 different known types of fibromuscular attachments between the long transverse process of the 7th cervical vertebra (C7), the apical region of a cervical rib, the first rib, or the pleural dome.

2. Cervical rib

Bony factors contributing to TOS pathogenesis include various types of cervical ribs, either in ligamentous form or as ossifications of anlage remnants. Simple variants merely involve widening of the transverse process of the 7th cervical vertebra, more developed  cervical ribs can extend as far as the middle of the first rib and touch it, while purely ligamentous forms extend anteriad to the sternoclavicular joint.

The estimated incidence of cervical ribs is 0.5% to 1%, of which only 5% to 10% become symptomatic. The incidence of cervical ribs in women is twice as high as in men.

3. Scalenus minimus muscle

This accessory muscle arises from the transverse process of the 7th cervical vertebra, travels between the brachial plexus and subclavian artery and inserts on the first rib or the pleural dome, thus constricting the scalene gap and also impeding access to it. In particular, carrying heavy loads and postural change through abduction of the arm increases compression of the neurovascular structures with associated complaints.

Other anatomic variants include, for example, steepening >45°of the first rib or a rudimentary first rib, hypertrophy of the scalene muscles, as well as variants of their insertions on the first rib, resulting in a narrowed angle between the anterior scalene muscle, first rib and clavicle, thereby displacing and compressing the neurovascular bundle.