Indmedica Home | About Indmedica | Medical Jobs | Advertise On Indmedica
Search Indmedica Web
Indmedica - India's premier medical portal

Journal of the Anatomical Society of India

Communication Between The Median And Musculocutaneous Nerve- A Case Report

Author(s): Chauhan, R. and Roy, T.S.

Vol. 51, No. 1 (2002-01 - 2002-06)

Department of Anatomy, All India Institute of Medical Sciences, New Delhi - INDIA

Abstract

Variations of the median and musculocutaneous nerve at the level of brachial plexus are common. The present report describes a case of variation of the median nerve observed in a 55 years old Indian female cadaver during routine educational dissection. Three nerve roots formed the median nerve, one each from the lateral and medial cords and the third root originating from the musculocutaneous nerve. The third root received separate communication from the musculocutaneous nerve. This abnormal root coming from the musculocutaneous nerve had a very close oblique course over the brachial artery. No accurate description of a similar case has been found in the literature. It is important to be aware of this variation while planning a surgery in the region of axilla or arm, as these nerves are more liable to be injured during operations. Possible mode of origin and clinical importance of such kind of variation has been discussed.

Key words: Median nerve, third root, anatomical variations.

Introduction:

Variations in the formation and branching of the brachial plexus are common and have been reported by several investigators (Kerr, 1918; Poynter, 1920; Linell, 1921; Hovelaque, 1927; Hirasawa, 1931; Miller, 1934; Bergman et al. 1988). The median, musculocutaneous and ulnar nerves after their origin from the brachial plexus, pass through the anterior compartment of the arm without receiving any branch from any nerve in the neighbourhood (Hollinshead, 1976; Williams et al., 1995). Although communications between the nerves in the arm are rare, the communication between the median nerve (MN) and musculocutaneous nerve (MCN) were described from nineteenth century (Testut, 1884, 1899; Villar, 1888; Harris, 1904). The lateral root of the MN carries fibres that may pass through the MCN, and a communicating branch from the later usually joins the MN in the lower third of arm (Kaus and Wotowicz, 1995; Bergman et al. 1988). In the arm, the MCN passes through the coracobrachialis muscle and innervates the coracobrachialis as well as the brachialis and the biceps brachii muscles and later continues as the lateral cutaneous nerve of the forearm without exhibiting any communication with the MN or other nerves. We recently observed multiple communications between the MCN and the MN in the upper arm that has not been reported in large clinical series or cadaveric studies. Our aim is to describe the exact topography of this variation and to discuss its morphological and clinical

significance. Knowledge of anatomical variation of these nerves at the level of upper arm is essential in light of the frequency with which surgery is performed in the axilla and the surgical neck of the humerus (Leffert, 1985).

Materials and Methods:

This study was conducted on 200 cadavers (400 upper limb specimens) dissected by the undergraduate students of All India Institute of Medical Sciences, New Delhi. The cadavers were embalmed through femoral arterial perfusion of 4% formaldehyde solution and preserved in weak formalin solution for more than one year before dissection. The brachial plexuses were dissected carefully and the variations from the normal usual pattern were noted, sketched and photographed.

Observations and Results:

We studied the origin and course of the MCN, MN and the ulnar nerve (UN) and their relationship with the surrounding structures. In the right upper limb of a female cadaver the MN had three roots; one each coming from the lateral cord, medial cord and the MCN. A thick lateral root originated from the lateral cord and joined the medial root to form the main trunk of the MN on the medial side of the axillary artery, 2.6 cm distal to the tip of the coracoid process. The UN arose independently from the medial cord of the brachial plexus, which continued as the medial root of the MN. The MN so formed had the same diameter as the ulnar nerve. The MCN was found to be communicating with the MN at two sites. A third root (TR) of the median nerve emerged from the MCN, which joined the MN 12.3 cm distal to the tip of the coracoid process, below the level of insertion of the coracobrachialis muscle (Fig. 1). The TR received a communicating branch from the MCN, 9.9 cm distal to the tip of coracoid process (Fig. 1, arrow). The TR of the MN and its communicating branch crossed the brachial artery superficially (Fig. 2). The remaining course of the MCN was unremarkable. It was also observed that the MCN did not penetrate through coracobrachialis muscle. The MN and the UN did not innervate any muscle in the anterior compartment of the arm.

Discussion:

Anastomosis between the MCN and the MN is by far the most common and frequent of all the variations that are observed among the branches of the brachial plexus (Venieratos and Anangnostopoulou, 1998). Fibres of the MN run along with the MCN, which after travelling some distance, leave the later to join the parent trunk (Williams et al, 1995). These communications between MN and MCN have been classified into five types (Le Minor, 1992). In type I, there is no communication between the MN and the MCN, in type II, the fibres of the medial root of the MN pass through the MCN nerve and join the MN in the middle of the arm, whereas in type III, the lateral root fibres of the MN pass along the MCN and after some distance, leave it to form the lateral root of the MN. In type IV, the MCN fibres join the lateral root of the MN and after some distance the MCN arises from the MN. In type V, the MCN is absent and the entire fibres of the MCN pass through the lateral root and fibres to the muscles supplied by MCN branch out directly from the MN. Connection between the MCN and MN in the present study could not be incorporated into any of the types described by Le Minor (1992) as it showed communication, which was not included in his description. Le Minor's description did not include multiple communications between these two nerves, a variation, which was observed in the present study. Venieratos and Anangnostopoulou (1998) have described only three types of communications between the MCN and MN in relation to the coracobrachialis muscle. In type I, communication between MCN and MN is proximal to the entrance of the MCN into the coracobrachialis, whereas in type II, the communication is distal to the muscle and in type III neither the nerve nor its communicating branch pierced the muscle. According to this classification the communication, noted in our study can be placed in type III, as the MCN did not pass through the coracobrachialis muscle. Therefore, we feel that with the exploration of new types of communications and anatomical variations, there may arise a need to modify the classification of Le Minor (1992), which could include not only the communication between the MN and the MCN but also the relationship of the MCN with the coracobrachialis.

The most frequent variation is the presence of a communicating branch that bifurcates from the MCN and goes distally to join the MN, an anastomosis observed in the lower third of arm (Venieratos and Anangnostopoulou, 1998; Bergman et al., 1988). If this branch is given off in upper third of the arm, it is generally considered as third (double lateral) root of the median nerve. The upper limb dissected in the present case, revealed that a branch of the MCN appeared in upper third of the arm, passed medially downwards and joined the MN in the lower third of the arm (Fig. 1). This branch was of the same diameter as the lateral root. Therefore, this is considered as the third root of median nerve or second lateral root. We report in addition to communication with the MN, the communicating third root also received a branch from the main trunk of the MCN. A variation which has not been reported yet was that the, so-called, third root of MN received a communicating branch from the MCN. Also, the third root passed superficial to the brachial artery. These kinds of variations are important, as it is more prone to injury in surgical operations of the axilla and upper arm.

The interpretation of the nerve anomaly of the arm requires consideration of the phylogeny and development of the nerves of the upper limb. Communication between the MCN and MN is considered as a remnant from the phylogenetic or comparative point of view. Imokawa (cited from Kosugi et al. 1986) reported that there was only one trunk equivalent to the MN in the thoracic limb of the lower vertebrates (amphibians, reptiles and birds). In the context that ontogeny recapitulates phylogeny, it is possible that the variation seen in the current study is the result of developmental anomaly. In man, the forelimb muscles develop from the mesenchyme of the para-axial mesoderm during fifth week of embryonic life (Larsen, 1997). The axons of spinal nerves grow distally to reach the limb bud mesenchyme. The peripheral processes of the motor and sensory neurons grow in the mesenchyme, in different directions (Brown et al. 1991; Williams et al. 1995). Although it is unclear why neuronal processes assemble to form a mixed nerve, in this complex developmental event, there are multiple possibilities for the route taken by developing axons and thus for their arrival at the main trunk. Once formed, any developmental differences would obviously persist postnatally (Brown et al. 1991). As the guidance of the developing axons is regulated by expression of chemoattractants and chemorepulsants in a highly coordinated site specific fashion any alterations in signaling between mesenchymal cells and neuronal growth cones can lead to significant variations (Sanes et al. 2000). Specifically, such developmental abnormalities for axonal guidance in the coracobrachialis muscle could readily produce a situation where the MCN does not pass through the coracobrachialis muscle, as seen here (Venieratos and Anangnostopoulou, 1998). Alternatively, the variation could arise from circulatory factors at the time of fusion of the brachial plexus cords (Kosugi et al. 1986).

Cases of communication between the MN and MCN or MN and UN have been reported (Srinivasan and Rhodes, 1981; Venieratos and Anangnostopoulou, 1998; Gümüsburun and Adigüzel, 2000; Choi et al. 2002). These variations are apparently not rare, and it is possible that the combined lesion of the MCN and part of MN would occur in injury of the lateral cord of the brachial plexus. Lesions of the communicating nerve may give rise to patterns of weakness that may impose difficulty in diagnosis. Clinical implication of this could be that injury of MCN proximal to the anastomotic branch between MCN and MN may lead to unexpected presentation of weakness of forearm flexors and thenar muscles (Sunderland, 1978). In diagnostic clinical neurophysiology, variations in connections between MN and MCN may have some significance (Choi et al. 2002). Variations that were observed in the present study involving MN and MCN might be of some importance to the surgeons. Knowledge of various communications between the MCN and the MN may prove valuable in traumatology of the shoulder joint, as well as in relation to repair operations (Benjamin et al. 1981; Ha'eri and Wiley, 1982; Seradge and Orme, 1982). To prevent unwanted outcomes of operations conducted on MCN, it is suggested that the presence of MN and MCN communications should be ruled out (Leffert, 1985).

Acknowledgement:

The authors acknowledge the contributions of undergraduate anatomy students (2000-2001 batch) and dissection hall technicians of the All India Institute of Medical Sciences, New Delhi for their help during dissection of the cadavers.

Reference:

  1. Bergman, R.A., Thompson, S.A., Afifi, A.K. and Saadeh, F.A.: Compendium of human anatomic variation. Urban & Schwarzeberg Munich. pp 139-143. (1988).
  2. Benjamin, A., Hirschowitz, D., Arden, G.P. and Blackburn, N. (1981): Doppelosteotomie am Schultergelenk. Orthopade. 10: 245-249.
  3. Brown, M.C., Hopkins, W.G. and Keynes, R.J.: Axon guidance and target recognition In : Essentials of neural development. Cambridge University Press. Cambridge. pp 46-66. (1991).
  4. Choi, D., Rodriguez-Niedenfuhr, M., Vazquez, T., Parkin, I. And Sanudo J.R. (2002): Patterns of connections between the musculocutaneous and median nerves in the axilla and arm. Clinical Anatomy. 15: 11-17.
  5. Gumusburun, E., Adiguzel, E. (2000): A variation of the brachial plexus characterized by the absence of the musculocutaneous nerve : case report. Surgical and Radiologic Anatomy. 22: 63-65.
  6. Haeri, G.B. and Wiley, A.M. (1982): Shoulder impingement syndrome, results of operative release. Clinical Orthopaedic. 168: 128-132.
  7. Harris, W. (1904): The true form of the brachial plexus. Journal of Anatomy and Physiology 38: 399-422.
  8. Hirasawa, K.O.: Untersuchengen uber das periphere Nervensystem, Plexus brachialis and die Nerven der oberen Extremitat. Arb Anat Inst Kaiserlichen Univ Kyoto A2: 135 136. (1931)Chauhan R. & Roy. T.S.
  9. Hollinshead, W.H.: Functional anatomy of the limbs and 27. Williams, P.L., Bannister, L.H., Berry, M.M., Collins, P., back. 4th Edn: W.B. Saunders, Philadelphia. pp 134-140. Dyson, M., Dussek, J.E. and Ferguson, M.W.J.: Gray's (1976). Anatomy In: Nervous system. 38th Edn; Churchill Livingston.
  10. Hovelacque, A.: Anatomie des nerfs craniens et rachidiens et Edinburgh. pp 1266-1274 (1995). du systeme grand symmthiqu. Gaston Doin et Cie. Paris. pp 483-491. (1927).
  11. Kaus, M. and Wotowicz, Z. (1995): Communicating branch between the musculocutaneous and median nerves in human. Folia Morphologica (Warsz). 54: 273-277.
  12. Kerr, A.T. (1918): The brachial plexus of nerves in man, the variations in its formation and branches. American Journal of Anatomy. 23: 285-395.
  13. Kosugi, K., Mortia, T., Yamashita, H. (1986): Brancing pattern of the musculocutaneous nerve. 1. Cases possessing normal biceps brachii. Jikeakai Medical Journal. 33: 63-71.
  14. Larsen, W.J.: Human Embryology In. Development of limbs. 2nd Edn; Churchill Livingstone. Edinburgh. pp 311-339. (1997).
  15. Le Minor, J.M. (1992): A rare variant of the median and musculocutaneous nerves in man. Archieves Anatomy Histology Embryology. 73: 33-42.
  16. Leffert, R.D.: Anatomy of brachial plexus In: Brachial Plexus injuries. Churchill Livingstone. New York. p 384. (1985).
  17. Linell, E.A. (1921): The distribution of nerves in the upper limb, with reference to variabilities and their clinical significance, Journal of Anatomy. 55: 79-112.
  18. Miller, R.A. (1934): Comparative studies upon the morphology and distribution of the brachial plexus. American Journal of Anatomy. 54: 143-147.
  19. Poynter, C.W.M.: Congenital anomalies of the arteries and veins of the human body with bibliography. University Studies. University of Nebraska 22: 1-106. (1920).
  20. Sannes, H.D., Reh, T.A. and Harris, W.A.: Development of the nervous system In: Axon growth and guidance. Academic Pres. New York. pp 189-197. (2000).
  21. Seradge, H. and Orme, G. (1982): Acute irreducible anterior dislocation of the shoulder. Journal of Trauma. 22: 330-332.
  22. Srinivasan, R. and Rhodes, J. (1981): The median-ulnar anastomosis (Martin-Gruber) in normal and congenitally abnormal fetuses. Archieves of Neurology. 38: 418-419.
  23. Sunderland, S.: Nerves and Nerve Injury In: The Median Nerve: Anatomical and Physiological features. 2nd Edn; Churchill Livingstone. Edinburgh. pp 672-677, 691-727. (1978).
  24. Testut, Trait: d'' Anatomie, 4th Edn; Vol 3. pp 176 (1899).
  25. Venieratos, D. and Anangnostopoulou, S. (1998): Classification of communications between the musculocutaneous and median nerves. Clinical Anatomy. 11: 327-331.
  26. Villar F. (1888): Quelques recherches sur les anastomoses des nerfs du membre superrieur. Bull. Scoc. Anat. De Paris. pp 607-615.

Missing Image

Fig. 1. Photograph of the dissected right upper arm showing branches of the brachial plexus. The biceps brachii muscle (BB) has been retracted laterally to expose the structures underneath. Note the branch of the musculocutaneous nerve (Mc), the third root (TR) joining the median nerve (MN) at the lower part of the arm. Another branch (with arrow) from the MCN joining the TR at the level of insertion of coracobrachialis muscle (Cb).

Missing Image

Fig. 2. Schematic diagram of figure. 1, note the branch to biceps brachii (nb) and Brachialis (br) from the MCN. BB Biceps Brachii, BA = Brachial Artery, LC = Lateral Cord, UN = Ulnar Nerve, MR & LR = Medial Root and Lateral Root of the median nerve.

Access free medical resources from Wiley-Blackwell now!

About Indmedica - Conditions of Usage - Advertise On Indmedica - Contact Us

Copyright © 2005 Indmedica