Potential compression of the musculocutaneous, median and ulnar nerves by a very rare variant of the coracobrachialis longus muscle.

The coracobrachialis longus muscle (CBL) is an extremely rare variant of the coracobrachialis muscle (CRM). The CBL originates from the apex of the coracoid process together with the short head of the biceps brachii and inserts on the olecranon of the ulna. The CBL consists of three parts: a superior part (classical CRM - length 137.88 mm), a middle fibrous layer (23.41 mm), and an inferior part (185.37 mm). A rare relationship between the CBL and median, musculocutaneous and ulnar nerves was observed with potential compression at these three parts. In addition, this case report describes a connection between CBL and the medial head of the triceps brachii, as well as a third head of the biceps brachii, which originate from the fibrous layer. This case report highlights the relationships between the CBL and the median, ulnar and musculocutaneous nerves.