50 - Bilateral Variant of the Interscalene Triangle and Accessory Coracobrachialis Muscle in a Female Cadaver: An Anatomical Case Report

Poster Board Number: 50
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Co-authors:

Ashraf Beshay - Georgetown University School of Medicine; Fan Cao - Georgetown University School of Medicine; Christopher Jaicks - Georgetown University School of Medicine; Iwanger-I-Ter Jia - Georgetown University School of Medicine; Caitlin Coker, PhD - Georgetown University School of Medicine

Abstract Body :This report details a case involving variations of the brachial plexus and subclavian artery at the interscalene triangle and an accessory coracobrachialis muscle. The interscalene triangle serves as a passageway for the brachial plexus and subclavian artery, which are vital for upper limb neurovascular supply and hold significant clinical importance, especially for specialties such as surgery and anesthesiology. Moreover, the coracobrachialis muscle is pierced by the musculocutaneous nerve, and its variations can hold clinical implications. During a routine dissection of a 94-year-old female anatomical donor, asymmetrical bilateral variations of the neurovasculature at the interscalene triangle were observed. A bilateral variation of the coracobrachialis muscle was also noted. Bilaterally, the C5 ventral ramus pierced the anterior scalene muscle and trifurcated into the suprascapular nerve, lateral cord contribution, and posterior cord contribution. On the right side, the subclavian artery also pierced the anterior scalene muscle through a separate intramuscular opening. Further dissection revealed a bilateral musculotendinous expansion of the coracobrachialis muscle that inserted on the medial epicondyle of the humerus. This accessory coracobrachialis muscle created a tunnel that transmitted the brachial artery and median nerve. The interscalene triangle variation described in this report can increase susceptibility to neurogenic and arterial thoracic outlet syndrome (TOS), compressing portions of the brachial plexus and subclavian artery by the anterior scalene muscle, leading to pain, sensory loss, and muscle weakness. Furthermore, patients with a brachial plexus variation are at risk of incomplete anesthesia during an interscalene nerve block due to the displacement of the target nerve bundle from what may be expected. Additionally, an accessory coracobrachialis muscle, especially when hypertrophied from exercise, creates a risk of brachial artery and median nerve compression. Imaging technologies are useful in mitigating the risks associated with anatomical variations in real time. However, procedures that use these technologies can be most efficient when medical practitioners develop and maintain a high awareness of potential anatomical variations. Clinical utilization of this knowledge will improve diagnostic accuracy, patient management, and treatment outcomes.