The co-occurrence of a four-headed coracobrachialis muscle, split coracoid process and tunnel for the median and musculocutaneous nerves: the potential clinical relevance of a very rare variation

Abstract

The coracobrachialis muscle (CBM) originates from the apex of the coracoid process, in common with the short head of the biceps brachii muscle, and from the intermuscular septum. Both the proximal and distal attachment of the CBM, as well as its relationship with the musculocutaneus nerve demonstrate morphological variability, some of which can lead to many diseases. The present case study presents a new description of a complex origin type (four-headed CBM), as well as the fusion of both the short biceps brachii head, brachialis muscle and medial head of the triceps brachii. In addition, the first and second heads formed a tunnel for the musculocutaneus and median nerves. This case report has clear clinical value due to the split mature of the coracoid process, and is a significant indicator of the development of interest in this overlooked muscle.

Keywords: Anatomical variations; Coracobrachialis muscle; Median nerve; Musculocutaneus nerve; Split coracoid.

Fig. 1

View of the three heads. Visible fusion with the short head of the biceps brachii. HH head of humerus, ACP apex of coracoid process, AACP accessory apex of coracoid process, 1 first head of coracobrachialis muscle, shBB short head of the biceps brachii, lhBB long head of the biceps brachii, B brachialis muscle. White arrowheads indicate the fusion between fourth head of the coracobrachialis muscle and brachialis muscle

Fig. 2

View after excision of short head of the biceps brachii. HH head of humerus, ACP apex of coracoid process, AACP accessory apex of coracoid process, 1 first head of coracobrachialis muscle, 2 the second head of the coracobrachialis muscle, 3 the third head of coracobrachialis muscle, 4 the fourth head of the coracobrachialis muscle, DM deltoid muscle, LC lateral cord of the brachial plexus, MCN musculocutaneus nerve, MN median nerve, AA axillary artery, lhBB long head of the biceps brachii, B brachialis muscle. The green circle indicates the musculocutaneus nerve ran between the first and the second head of the coracobrachialis muscle. The red circles show the place, where the median nerve ran between the first and the second head of the coracobrachialis muscle (color figure online)

Fig. 3

Insertion of the coracobrachialis muscle. CBM coracobrachialis muscle, B brachialis muscle, 1 first head of coracobrachialis muscle, 2 the second head of the coracobrachialis muscle, 3 the third head of coracobrachialis muscle, mhTB medial head of the triceps brachii. Blue arrowhead shows a connection of first and second heads of the coracobrachialis muscle. Yellow arrowhead show a connection between the third head of CBM and first and second heads joined together. White arrowheads show the connection between CBM and the medial head of the triceps brachii (color figure online)

Fig. 4

Extracted coracobrachialis muscle with nerves and arteries. 1 first head of coracobrachialis muscle, 2 the second head of the coracobrachialis muscle, 3 the third head of coracobrachialis muscle, 4 the fourth head of the coracobrachialis muscle, MCN musculocutaneus nerve, MN median nerve, LC lateral cord of the brachial plexus, MC medial cord of the brachial plexus, AA axillary artery

Fig. 5

Scapula. A acromion, G glenoid fossa, BCP base of coracoid process, MP midportion, ACP apex of coracoid process, AACP accessory apex of coracoid process

Fig. 6

Scapula. A acromion, G glenoid fossa, BCP base of coracoid process, MP midportion, ACP apex of coracoid process, AACP accessory apex of coracoid process

Fig. 7

Scapula. A acromion, G glenoid fossa, BCP base of coracoid process, MP midportion, ACP apex of coracoid process, AACP accessory apex of coracoid process

Fig. 8

Relationship between the coracobrachialis and musculocutaneus nerve and the median nerve. 1 first head of coracobrachialis muscle, 2 the second head of the coracobrachialis muscle, 3 the third head of coracobrachialis muscle, LC lateral cord of the brachial plexus, AA axillary artery, MCN musculocutaneus nerve, MN median nerve. The green circle indicates the musculocutaneus nerve ran between the first and the second head of the coracobrachialis muscle. The red circles show the the place, where the median nerve ran between the first and the second head of the coracobrachialis muscle (color figure online)