Multiple anomalies of the brachial plexus : a case report

The brachial plexus is situated in the posterior triangle of the cervical region and in the axilla. This plexus is a union of the lower four cervical (C5, C6, C7, and C8) ventral rami and the first thoracic (T1) ventral ramus. At the lateral border of the anterior scalene muscle, the five roots unite to form the upper, middle, and lower trunks, each of which splits into anterior and posterior divisions in the floor of the posterior triangle of the neck. At the upper border of the first rib, the divisions join to form lateral, medial, and posterior cords. Just distal to the inferior border of the pectoralis minor muscle, near the third part of the axillary artery, the cords give off their terminal branches, including the axillary, musculocutaneous, radial, median, and ulnar nerves [1–4]. The scalene muscles are known as the paravertebral muscles and comprise anterior, middle, posterior, and minimus. Anterior scalene muscle arises from the anterior tubercles of the transverse processes of the third to sixth cervical vertebrae. It passes anterolaterally to be inserted by a narrow tendon on the upper surface of the first rib between the grooves for the subclavian vein and subclavian artery. The middle scalene muscle arises from the posterior tubercles and costotransverse bars of transverse processes of all or most of the cervical vertebrae. It inserts into the upper border of the first rib between the groove for the subclavian artery and the scalene tubercle. The brachial plexus and subclavian artery emerge between anterior and middle scalene muscles. The posterior scalene muscle arises from the posterior tubercles of the fourth to sixth cervical vertebrae and is inserted into the outer surface of the second rib [5]. The abnormalities of scalene muscles may result in compression to subclavian artery or brachial plexus in the root of the neck.