A rare anomaly of the cervicobrachial plexus: penetration of the anterior scalene muscle tendon by the T1 nerve root.

Abstract

The cervicobrachial plexus is known to exhibit anatomical variation, particularly the brachial plexus, which maintains a close anatomical relationship with the subclavian artery and the scalene muscles. Knowledge of these structural variations is critical for clinicians involved in the diagnosis and management of brachial plexus injuries. This case report describes a rare case involving multiple anomalies in the root formation of the brachial plexus, observed in a Japanese male cadaver. In this case, both brachial plexuses were formed from C4 to T1, and the both subclavian arteries passed between C8 and T1. Notably, the right T1 nerve root penetrated the insertion tendon of the anterior scalene muscle. In addition, the right subclavian artery also penetrated the insertion of the anterior scalene muscle. On the left side, further anatomical variations were observed, including anomalies in the intermediate supraclavicular nerve, the cervical ansa, and the dorsal scapular artery. The configuration in which the T1 nerve root penetrates the anterior scalene muscle tendon has not been previously reported and may have important clinical implications. These findings underscore the importance of careful preoperative assessment of the anatomical relationship between the T1 nerve root and the anterior scalene muscle during brachial plexus blocks via the interscalene approach, neurogenic thoracic outlet syndrome, and surgical procedures in the cervical and upper limb regions.