An accessory middle scalene muscle causing thoracic outlet syndrome.

The aim of our study is to present a very rare accessory middle scalene muscle, leading to thoracic outlet syndrome. In particular, a muscular bundle was discovered on a male cadaver connecting the middle portion of the middle scalene muscle with the anterior scalene muscle insertion to Lisfranc's tubercle. This triangular accessory muscle and, especially, its sharp medial border compressed the middle and lower trunk of the brachial plexus and...