The increased incidence of motor vehicle accidents during the past century has been associated with a significant increase in brachial plexus injuries. New imaging studies are currently available for the evaluation of brachial plexus injuries. Myelography, CT myelography, and magnetic resonance imaging (MRI) are indicated in the evaluation of brachial plexus. Moreover, a series of specialized electrodiagnostic and nerve conduction studies in association with the clinical findings during the neurologic examination can provide information regarding the location of the lesion, the severity of trauma, and expected clinical outcome. Improvements in diagnostic approaches and microsurgical techniques have dramatically changed the prognosis and functional outcome of these types of injuries. 1. Introduction Brachial plexus is a complex network of nerves, which is responsible for the innervation of the upper extremity. It is formed in the posterior cervical triangle by the union of ventral rami of 5th, 6th, 7th, and 8th cervical nerve roots and 1st thoracic nerve root. This composite nerve network can be divided into roots, trunks, divisions, and cords. The roots, trunks, and divisions lie in the posterior triangle of the neck, whereas the cords lie in the axillary fossa. Cords are further divided in the major nerve branches of the upper extremity [1] (Figure 1). Figure 1: Classic form of brachial plexus. Roots and trunks lie in the supraclavicular space; the divisions are located posterior to the clavicle, while cords and branches lie infraclavicularly [2]. Branches that arise from different portions of brachial plexus are shown in the following figure (Figure 2). Figure 2: Roots, trunks, divisions, cords, and terminal branches of brachial plexus. All three cords of the plexus lie above and laterally to the medial portion of axillary artery. Medial cord crosses the artery, passing inferiorly, to reach the medial surface of the middle portion of the artery. Posterior cord is located behind the middle portion of the artery and lateral cord lies laterally to the middle portion of the artery. The names of the cords of brachial plexus imply their relationship to the middle portion of the axillary artery (Figure 3). Figure 3: Relationships of brachial plexus and its portions of the axillary artery. Anatomic variants of brachial plexus are observed in more than 50% of the cases [3]. Most common variants are associated with the contribution of C4 (prefixed) or with the contribution of T2 nerve root to the plexus (postfixed) (Figure 4). It is estimated that C4 nerve root
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