Cadaveric Report of an Unusual Axillary Artery Branching Variation: A Potential Compression Site for the Lateral Root of the Median Nerve.

The median nerve is formed by the union of lateral and medial roots originating from the lateral and medial cords of the brachial plexus, respectively. The lateral root of the median nerve is responsible for motor innervation to some of the anterior forearm muscles as well as sensory innervation to the lateral palm and the palmar surfaces of the lateral three-and-a-half digits. While anatomical variations in the axillary artery's branching pattern are relatively common, vascular compression of the median nerve, particularly its individual roots, is exceedingly uncommon. In this report, we observed that the distal part of the axillary artery gave rise to a single large-caliber common trunk. The lateral root of the median nerve was found to be clamped between the distal axillary artery and its common trunk branch, which formed a dynamic acute arterial angle that narrowed further upon abduction of the arm. At 90 degrees of abduction, the angle was obliterated; this resulted in direct compression of the nerve root between the two arteries. No atrophy was noted in the muscles of the forearm, suggesting the compression may have been intermittent or subclinical. Additionally, the tortuosity of the proximal brachial artery observed in this case may reflect long-term compensatory changes due to restricted arterial mobility. This case highlights a previously unreported potential site of compression of the lateral root of the median nerve by a vascular anomaly. The findings underscore the importance of recognizing such variations during clinical assessments and surgical procedures involving the axilla.