Absence of Musculocutaneous Nerve: Two Case ReportsP.V.V. PRASADA RAO* AND S.C. CHAUDHARY

Department of Anatomy, University of Zimbabwe, Harare, Zimbabwe

Anomalies of the brachial plexus including its terminal branches as well as the course anddistribution of the nerves in the upper limb have been reported in the literature. Two cases ofabsent musculocutaneous nerve from the lateral cord of the brachial plexus encounteredduring routine gross anatomical dissection are reported. The median nerve took over the areaof supply of the musculocutanoeus nerve by giving both the muscular and sensory branches.Out of 24 upper limbs dissected, the musculocutaneous nerve was found to be absent in 8%of the cases. The clinical implications of the absent musculocutaneous nerve and its etiologyin light of its development is discussed. Clin. Anat. 14:31–35, 2001.© 2001 Wiley-Liss, Inc.

Key words: brachial plexus; musculocutaneous nerve; median nerve; lateralcord; variations; absence

INTRODUCTION

Anomalies of the brachial plexus formation and itsterminal branches are not uncommon and Buch-Han-sen (1955) observed these variations in 65.3% of cases.The musculocutaneous nerve is a motor and sensoryperipheral nerve, which originates from the lateralcord of the brachial plexus in the axilla. Variations inthe course of the musculocutaneous nerve and itsbranches have been previously reported (Bergman etal., 1988; Williams, 1995). The musculocutaneousnerve was reported to be absent by Ihunwo et al.(1997). The musculocutaneous nerve has been shownto communicate with the median nerve in the upperarm (Chiarapattanakom et al., 1998; Eglseder andGoldman, 1997; Kosugi et al., 1992; Sunderland et al.,1959).

The median nerve is generally described as nothaving any muscular branches in the upper arm, ex-cept in some instances a variable muscular branch tothe pronator teres given off above the elbow (Wil-liams, 1995). The musculocutaneous nerve usuallysupplies the coracobrachialis, biceps brachii, and thebrachialis muscles in the anterior compartment of theupper arm and then continues as the lateral cutaneousnerve of the forearm. Two cases of absent musculo-cutaneous nerve from the lateral cord of the brachialplexus were encountered during routine gross ana-tomical dissection. The median nerve took over theinnervation of the anterior compartment muscles ofthe upper arm. This report will assist clinicians and

the surgeons by pointing out anatomical anomaliesassociated with the origin of musculocutaneous nerveand variations in the origin of muscular branches tothe anterior compartment muscles of the upper arm.

MATERIALS AND METHODS

Twenty-four upper extremities were dissected witha sex and race distribution of 11 males, one female; sixwhites, five blacks, respectively. The branches of var-ious cords of the brachial plexus in the axilla weredissected. If the musculocutaneous nerve was notseen originating from the lateral cord of the brachialplexus, the roots of formation of the median nervewere dissected. The course and the branches of themedian nerve to the upper arm muscles were noted.The site of origin of the branches from the mediannerve in the upper arm was identified and the lengthof the median nerve before the origin of thesebranches was measured. The muscular branches tothe muscles of the anterior compartment of the upperarm were dissected and their origins noted. The siteswhere the nerves supplied the muscles were identi-fied and their lengths measured.

*Correspondence to: Dr. P.V.V. Prasada Rao, Department of Anat-omy, University of Zimbabwe, P.O. Box MP 167, Harare, Zim-babwe. E-mail: prasada@compcentre.uz.ac.zw

Received 6 October 1999; Revised 18 February 2000

Clinical Anatomy 14:31–35 (2001)

© 2001 Wiley-Liss, Inc.

CASE REPORTS

Two cases of absent musculocutaneous nerve wereobserved during gross anatomical dissection.

Case one: Musculocutaneous nerve was absent inthe right limb of a white male aged 89 years. Thelateral cord of the brachial plexus gave a lateral pec-toral branch and a muscular branch to the coracobra-chialis, which crossed the shoulder joint and suppliedthe muscle 3.2 cm from the coracoid process. Themedian nerve was formed in front of the axillary arteryby the union of the lateral root, which was a continu-ation of the lateral cord, and the medial root from themedial cord forming a clasping relationship with theaxillary artery. The contribution of the lateral root tothe median nerve was much larger than the medialroot. The median nerve then crossed the axillary ar-tery, ran downward and medial to the axillary artery inthe axilla, and then on the medial side of the brachialartery in the upper arm.

A common branch arose from the median nerve 3.7cm following its formation at the level of the upperborder of the teres major muscle, ran downward andlaterally for about 5 cm on the way crossing the bra-chial artery anteriorly. The common branch gave mus-cular branches to biceps brachii and brachialis after 1.5cm and 5.7 cm of its course. The common branch thencontinued downward and laterally anterior to the bra-chialis muscle, pierced the lateral intermuscular sep-tum of the upper arm at about 3.5 cm above the inter

condylar line of the humerus as the lateral cutaneousnerve of the forearm (Fig. 1).

Case two: Musculocutaneous nerve was absent inthe right limb of a black male, aged 50 years. Thelateral cord of the brachial plexus gave a lateral pec-toral branch and a muscular branch to the coracobra-chialis muscle, which crossed the shoulder joint beforeit supplied the muscle. The median nerve was formedby the fusion of the lateral root coming as a continu-ation of the lateral cord and the medial root from themedial cord, anterior to the axillary artery. The lateralroot contribution to the median nerve was larger thanthe medial root contribution. The median nerve randownward and laterally, crossed the axillary artery onits way and ran lateral to the axillary artery in the axillaand then lateral to the brachial artery in the upper halfof the upper arm. The median nerve then crossed thebrachial artery in front and continued medial to thebrachial artery in the lower half of the upper arm.

The median nerve gave muscular branches to cor-acobrachialis and biceps brachii at 1.3 cm and 9.7 cmfollowing its formation and ran for about 3.7 cm and2.5 cm, respectively, before they supplied the mus-cles. Just before it crossed the brachial artery, themedian nerve gave a common branch 13.5 cm follow-ing its formation which ran downward and laterallyand gave a small branch which supplied the brachialismuscle on its medial border. The common branchthen continued further downward laterally on the an-

Fig. 1. Anterior view of right arm: absent musculocutaneous nerve: (1) common branch: mediannerve, (2) median nerve, (3) nerve to biceps brachii, (4) nerve to brachialis, and (5) lateral cutaneous nerveof forearm.

32 Rao and Chaudhary

terior surface of the brachialis muscle in the lowerthird of the arm, deep to the biceps brachii muscle andpierced the lateral intermuscular septum at about 2.6cm above the inter condylar line of the humerus as thelateral cutaneous nerve of the forearm (Fig. 2).

DISCUSSION

The musculocutaneous nerve after its origin fromthe lateral cord normally pierces the coracobrachialismuscle in the upper part of the arm. It then gives abranch to the coracobrachialis muscle and continuesits course lateral to the brachial artery between thebrachialis and the biceps brachii muscles and givesmuscular branches to both the biceps and brachialis. Itthen continues as the lateral cutaneous nerve of theforearm. We observed two cases of absent musculo-cutaneous nerve out of 24 dissected upper limbs thusmaking the incidence rather high given that the re-ported cases were only four in the last 32 years. In onecase, a single branch of the median nerve supplied allthe anterior compartment muscles of the upper arm,which further down continued as the lateral cutaneousnerve of the forearm. In the second case, separatemuscular branches to the coracobrachialis and bicepsbrachii arose from the median nerve and the lateralcutaneous nerve of the forearm also arose from themedian nerve in common with the muscular branch tothe brachialis muscle. In the cases reported here, the

lateral root contribution to the median nerve waslarger than the medial root since the median nerve hastaken over the area of supply of musculocutaneousnerve. Absence of the musculocutaneous nerve indi-cated that the nerve fibers of C5 and C6 passed via thelateral root to the median nerve and then distributedto muscles in the anterior compartment of the upperarm as well as anterolateral cutaneous area of theforearm through the branches of the median nerve. Inone case, two branches supplied the coracobrachialismuscle, one arising directly from the lateral cord andanother from the median nerve. According to Williams(1995), the coracobrachialis branch arising from thelateral cord may contain fibers from the seventh cer-vical ramus whereas the other coracobrachialis brancharising from the median nerve contains the fibers fromboth the fifth and sixth cervical rami, which normallypass through the musculocutaneous nerve.

Complete absence of the musculocutaneous nerveand a complete takeover of the innervation of thecoracobrachialis, biceps brachii, and the brachialismuscles by the median nerve is an unusual variationof the brachial plexus (McMinn, 1994; Moore, 1992;Williams, 1995). Reference is sometimes made to thepresence of a communicating branch between themusculocutaneous nerve and the median nerve (Wil-liams, 1995). Venieratos and Anagnostopoulou (1998)classified the communications between the musculo-cutaneous and median nerves as Type I and Type II

Fig. 2. Anterior view of right arm: absent musculocutaneous nerve (1) nerve to coracobrachialis, (2)nerve to biceps brachii, (3) median nerve, (4) common branch: median nerve, (5) nerve to brachialis, and(6) lateral cutaneous nerve of forearm.

Absent Musculocutaneous Nerve 33

depending on whether the communicating brancharose from the musculocutaneous nerve before or afterit pierced the coracobrachialis muscle, and Type IIIwhen the musculocutaneous nerve did not pierce thecoracobrachialis muscle.

Nakatani et al. (1997) reported an anomaly of thebrachial plexus including the absence of anterior andposterior divisions of its middle trunk and communi-cations between various cords of the brachial plexus.They also reported absence of the musculocutaneousnerve with branches of the lateral cord directly sup-plying the coracobrachialis, biceps brachii, and bra-chialis muscles. The lateral cutaneous nerve of theforearm also arose from the lateral cord, which alsoreceived a small contribution from the median nerve.The medial and lateral roots of the median nerve didnot unite in the axilla but were united in the upperarm about 5 cm distal to the lower border of thelatissimus dorsi muscle. Adachi (1928) and Buch-Han-sen (1955) also observed the union of medial andlateral roots in the upper arm and not in the axillaryregion. Ihunwo et al. (1997) reported a case of bilateralabsence of the musculocutaneous nerve from the lat-eral cord of the brachial plexus with four branchesarising from the lateral side of the median nerve. Thefirst three were muscular branches to the coracobra-chialis, biceps brachii, and brachialis muscles and thelast branch continued as the lateral cutaneous nerve ofthe forearm. The branch to the pronator teres alsoarose from the medial side of the median nerve abovethe elbow. Le Minor (1990) also reported the absenceof musculocutaneous nerve with branches from thelateral cord directly supplying the coracobrachialis,biceps brachii, and brachialis muscles. The lateralcutaneous nerve of the forearm also arose from thelateral cord. The lateral root to the median nerveoriginated from the lateral cord at the middle of theupper arm after the origin of muscular branches.

Nakatani et al. (1997) and Le Minor (1990) ob-served the absence of the musculocutaneous nervefrom the lateral cord of the brachial plexus andbranches from the lateral cord directly supplied theanterior compartment muscles of the upper arm.Moreover, they observed the formation of mediannerve by the union of lateral root with the medial rootin the upper arm, and the lateral root was in fact acontinuation of the lateral cord after giving the mus-cular branches. In the cases reported here, the mediannerve was formed in the axilla and there was a com-plete absence of the musculocutaneous nerve fromthe lateral cord of the brachial plexus. The muscularbranches to the anterior compartment of the upperarm arose from the median nerve either directly orindirectly, and also the lateral cutaneous nerve of the

forearm, which were normally given off by the mus-culocutaneus nerve in the upper arm. These observa-tions are similar to the one reported by Ihunwo et al.(1997) except that we did not observe the muscularbranch to the pronator teres from the median nerve inthe upper arm. In the present study, the musculocu-taneous nerve was absent on the right side, whereasNakatani et al. (1997) and Le Minor (1990) observedit on the left side and Ihunwo et al. (1997) observed itbilaterally.

From the embryological studies done by Iwata(1960), the brachial plexus appeared as a single radic-ular cone in the upper limb, which was divided intoventral and dorsal segments. The ventral segmentgave roots to the median and the ulnar nerves. Themusculocutaneous nerve arose form the mediannerve. This study confirms the primitive embryologi-cal origin of the musculocutaneous nerve from themedian nerve, which was retained in these two casesand the median nerve supplied the anterior compart-ment muscles either by a common branch or by sep-arate muscular branches.

The clinical implication of this variation is thatinjury to the median nerve in the axilla would, inaddition to the effects in the hand, result in the pa-ralysis of the coracobrachialis, biceps brachii, and themedial part of the brachialis muscles. It would alsoproduce a weak flexion at the elbow and a very weaksupination of the flexed elbow. Loss of sensation onthe lateral surface of the forearm could also follow.The musculocutaneous nerve absence is not only ofinterest to the anatomists but also to the clinicians andsurgeons.

ACKNOWLEDGMENTS

We thank Mr. W. Makowa for his technical assis-tance as well as Miss F. Matsenga for typing thismanuscript.

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