Musculocutaneous nerve arises from the lateral cord (C5,6,7) of brachial plexus. Communications between the branches of brachial plexus are not so common. During routine dissection, we observed bilateral variation in 60-year-old female cadaver. In the present case, median nerve represented as a musculocutaneous nerve which supplied biceps brachii and brachialis, further continued into forearm as lateral cutaneous nerve of forearm on the right arm. This branch did not pass through coracobrachialis muscle but the coracobrachialis was innervated by a branch from lateral cord of brachial plexus. We also observed an abnormal communicating branch between the musculocutaneous and median nerve on left side of the arm. These kinds of variations are important for surgeons while performing surgeries of axilla and upperlimb

Ahmed Peer, S

Indira Devi, B

Raju, S

Udaya Kumar, P

English

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Bilateral variation of musculocutaneous nerve                                   Raju S et al. Journal of Surgical Academia 2013; 3(1):13-15   13       An Unusual Bilateral Variation of Musculocutaneous Nerve  Raju S (), Udaya Kumar P, Ahmed Peer S, Indira Devi B  Department of Anatomy, RIMS Medical College, Rajiv Gandhi Institute of Medical Sciences, Kadapa- 516002, Andhra Pradesh, India.   Abstract  Musculocutaneous nerve arises from the lateral cord (C5,6,7) of brachial plexus. Communications between the branches of brachial plexus are not so common. During routine dissection, we observed bilateral variation in 60-year-old female cadaver. In the present case, median nerve represented as a musculocutaneous nerve which supplied biceps brachii and brachialis, further continued into forearm as lateral cutaneous nerve of forearm on the right arm. This branch did not pass through coracobrachialis muscle but the coracobrachialis was innervated by a branch from lateral cord of brachial plexus. We also observed an abnormal communicating branch between the musculocutaneous and median nerve on left side of the arm. These kinds of variations are important for surgeons while performing surgeries of axilla and upperlimb.  Keywords: Brachial plexus, communication, median nerve, musculocutaneous nerve, lateral cutaneous nerve of forearm.    Correspondence: Raju Sugavasi, Department of Anatomy, RIMS Medical College, Rajiv Gandhi Institute of Medical Sciences, Kadapa- 516002, Andhra Pradesh, India. Tel: +91-9849501978. Fax: 220200-9701501045–22022. Email: anatraju@yahoo.co.in  Date of submission: 31 Aug, 2012                Date of acceptance: 26 Feb, 2013   Introduction  Musculocutaneous nerve (MCN) is the nerve of anterior compartment of arm. It arises from the lateral cord of brachial plexus (C5,6,7) at the lower border of pectoralis minor. It passes through coracobrachialis muscle, and also supplying to it, later innervates both heads of biceps brachii and brachialis muscles, then enters the cubital fossa, lateral to the biceps tendon where it continues as the lateral cutaneous nerve of forearm. The median nerve (MN) has two roots from the medial (C8,T1) and lateral (C5,6,7) cords of the brachial plexus formed at lateral to third part of axillary artery, then passes through anterior compartment of arm crossing the brachial artery from lateral to medial side enters into the cubital fossa (1). Bilateral variations of terminal branches of the brachial plexus are uncommon.  Case Report  During routine dissection in the department of Anatomy, we observed bilateral variations in the anterior compartment of the arm region in 60-year-old female cadaver. In the right upper arm the motor branches to the biceps brachii and brachialis muscles found to arise from the branch of the right median nerve (Fig. 1) and the same nerve continued as the lateral cutaneous nerve of forearm. This branch was not passing through the coracobrachialis muscle, but this muscle was innervated by direct branch from lateral cord of brachial plexus. We also observed another variation at left side of arm where MCN and MN communicated by an abnormal communicating branch (Fig. 2), which measured about 5 cm in length.   Discussion  In present case, it was found that MN innervated the brachialis and the biceps brachii and the MCN was reported to be absent. Previous studies reported the MCN was absent or not separated from MN (2,3,4,5,6,7) but its real prevalence is still remains unknown.  Case Report Bilateral variation of musculocutaneous nerve                                   Raju S et al. Journal of Surgical Academia 2013; 3(1):13-15   14                 Figure 1: Right side of Arm showing Cb: Coracobrachialis, Bb: Biceps brachii, Bh: Brachialis, Mn: Median nerve, Ncb: Nerve to coracobrachialis, Nbb: Nerve to Biceps brachii, Lcnf: Lateral cutaneous nerve of forearm.                  Figure 2: Left side of Arm showing Mn: Median nerve, Mcn: Musculo cutaneous nerve, Cn: Communication, Bb: Biceps brachii, Lcnf: Lateral cutaneous nerve of forearm.    Musculocutaneous nerve did not pierce the coracobrachialis muscle in three cases (8) similar to the present case.  According to Le Minor (9), variations in the communications between MN and MCN classified as 5 types, in type I there is no communication between the MN and MCN. In type II the fibres of medial root of MN pass through MCN and join the MN in the middle of the arm, in type III MN and MCN run together later that lateral root of MN separates from it. In type IV MCN arises from median nerve after joining to lateral root of the MN. In type V MCN is absent. The fibers of the MCN run within the MN along its course. In this type the MCN does not pierce the coracobrachialis muscle. Veinreratos and Anagnostopolou conducted studies on 79 cadavers and found communications between mcn and mn in 22 cadavers (10) and they reported the following three types of communications between MCN and MN, in relation to coracobrachialis muscle. In type I the communication was proximal to the entrance of the MCN into the coracobrachialis (9/22), in type II it was distal to the muscle (10/22) and in type III the nerve did not pierce the muscle (3/22). So according to this classification the present variation, fits to type III. Lokanadham (11), Chauhan (12) Himabindhu (13) who reported the communications between median nerve and musculo cutaneous nerve.  Conclusion   The present variation was found to be bilaterally which not yet reported, so the knowledge of anatomical variations of these nerves at the level of upper arm is essential while performing surgeries in the axilla and post-traumatic evaluations and exploratory interventions of the arm for peripheral repair.  References  1. Standring S, Borley NR, Collins P, Crossman AR, Gatzoulis MA, Healy JC, et al. Gray’s Anatomy. 40th Ed. London: Churchill Livingstone, 2008, pp-791–822.  2. Henry Holinshed W. Anatomy for surgeons: vol.3 (The Back and Limbs). 3rd Ed., Philadelphia:Harper & Row, 1982, pp-366.   3. Prasada Rao PV, Chaudhary SC. Communication of the musculocutaneous nerve with the median nerve. East Afr Med J 2000;77(9):498-503.  4. Beheiry EE. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol 2004;63(3):313-318.  5. Arora L, Dhingra R. Absence of musculocutaneous nerve and accessory head of biceps brachii: a case report. Indian Journal of Plastic Surgery 2005; 38(2): 144-146.   6. Nayak S. Absence of musculocutaneous nerve associated with clinically important variations in the formation, course and distribution of the median nerve – a case report. Neuroanatomy  2007; 6: 49-50.   7. Rajendrakumar V. Absence of musculocutaneous nerve in the left axilla. IJAV 2009; 2: 140–142.   8. Nakatani T, Mizukami S, Tanaka S. Three cases of the musculocutaneous nerve not perforating Bilateral variation of musculocutaneous nerve                                   Raju S et al. Journal of Surgical Academia 2013; 3(1):13-15   15  the coracobrachialis muscle. Kaibogaku Zasshi 1997;72(3):191-4.  9. Le Minor JM. A rare variation of the median and musculocutaneous nerves in man. Arch Anat Histol Embryol 1990;73:33-42.  10. Venieratos D, Anagnostopoulou S. Classification of communications between the musculocutaneous and median nerves. Clin Anat 1998;11(5):327-31.  11. Lokanadham S, Subhadra Devi V. Anatomical variation Communication between musculocutaneous nerve and median nerve. Int J Biol Med Res 2012; 3(1): 1436-1438.  12. Chauhan R, Roy TS. Communication between the Median and Musculocutaneous Nerve. A Case Report. J Anat Soc India 2002; 51(1): 72-75.   13. HimaBindu A and Narsinga Rao B. Short musculocutaneous nerve and unusual innervation of median nerve. JMS 2012; 2 (2): 166-169.  

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