





















































Formation of median nerve by three roots A case report


Formation of median nerve by three roots: A case report

N. Satyanarayana1, C.K. Reddy2, P. Sunitha3, N. Jayasri4, V. Nitin5, G. Praveen6, R. Guha7, A.K. Datta8, M. M. Shaik9

1, 5, 6Lecturer in Anatomy,  2Associate Prof in Anatomy, PIMS, Karimnagar, India, 3Lecturer in Physiology ,  7,8Professor in

Anatomy, 9Lecturer in Pharmacology, College of Medical Sciences, Bharatpur, Nepal, 4Professor & Head, Dept of Anatomy,

CAIMS, Karimnagar

Abstract:

During routine dissection of an adult male cadaver in the Department of Anatomy, College of Medical

Sciences, Bharatpur, Nepal, the right median nerve was found to be formed by three roots. The finding

was noted after thorough and meticulous dissection of the upper limbs of both sides (axilla, arm, forearm

and palm). Out of the three roots forming the anomalous median nerve, two were from lateral cord and

one from medial cord of brachial plexus. However, the distribution of the anomalous median nerve was

normal in arm, forearm and palm. The arterial pattern in the arm (axillary and brachial arteries) was

also normal.

Key words: Cadaver, median nerve, brachial plexus

Case report:

During routine dissection of an adult male cadaver

in the Department of Anatomy, College of Medical

Sciences, Bharatpur, Nepal, anomalous median nerve

with regard to its formation was found. Dissection of

both the upper limbs (axilla, arm, cubital fossa, forearm

and palm) was done thoroughly and meticulously to find

out the mode of formation, relations and distribution of

the anomalous right median nerve and the status of the

left median nerve.

It was found that the right median nerve was

formed by three roots, two coming from lateral cord

and one from medial cord of brachial plexus.

The uppermost or highest root was noted to be at the

level of origin of coracobrachialis muscle. The second

root was found to be immediately below the first one.

These two roots were found to be passing obliquely in

front of second and third part of axillary artery and

joining individually with the medial root of median nerve

and forming median nerve trunk, in front of third part

of axillary artery. (Figure No.-1)

Further distribution of the anomalous median nerve

in the arm, forearm and palm was normal. The arterial

pattern in arm was also normal. The left median nerve

was also normal.

Discussion:

The median nerve is normally formed by the union

of two roots: lateral root of median nerve  coming from

the lateral cord (C5, C6, C7) of brachial plexus and

medial root of median nerve  coming from the medial

cord (C8, T1) of brachial plexus. The two roots

embrace the third part of the axillary artery, uniting

anterior or lateral to it. Some fibres from C7 often leave

the lateral root in the lower part of the axilla passing
Correspondences: Dr. N. Satyanarayana

E-mail: satyam_n19@yahoo.com

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distomedially posterior to the medial root, usually

anterior to axillary artery, to join the ulnar nerve: they

may branch from the seventh cervical ventral ramus.

Clinically they are believed to be mainly motor to the

flexor carpi ulnaris.

The median nerve enters the arm at first lateral to

the brachial artery. Near the insertion of the

coracobrachialis, it crosses in front of (rarely behind)

the artery, descending medial to it, to the cubital fossa,

where it is posterior to the bicipital aponeurosis and

anterior to the brachialis, separated by the latter from

the elbow joint. It usually enters the forearm between

the heads of the pronator teres, crossing to the lateral

side of the ulnar artery and separated from it by the

deep head of pronator teres.1

Variations in the formation of median nerve were

noted by some earlier workers. However, most of the

variations as presented by them were related to

anomalous relationship between median and

musculocutaneous nerves. Chauhan and Roy (2002)

reported formation of median nerve by two lateral and

one medial root.2 Same observation was reported by

Saeed and Rufai (2003).3

Satyanarayana and  Guha (2008) reported

formation of median nerve by four roots (three lateral

and one medial root).4

In other study, it was found that the lateral root

was small and the musculocutaneous nerve was

connected with median nerve in the arm.5

Another study involving dissection of ten cadavers,

mentioned failure of separation of musculocutaneous

nerve from the median nerve and the latter therefore

gave off the branches that should arise from

musculocutaneous nerve, namely branches to

coracobrachialis, biceps brachii and major part of

brachialis.6

However the variation related to the formation of

median nerve by more than two roots which were

observed in the present study is rare as revealed by

survey of literatures.

Such variation can be explained in the light of

embryogenic development.

The first indication of limb musculature is observed

in the seventh week of development as condensation

of mesenchyme near the base of the limb buds.

With further elongation of the limb buds, the muscle

tissue splits into flexor and extensor compartments.

The upper limb buds lie opposite the lower five

cervical and upper two thoracic segments. As soon as

the buds form, ventral primary rami from the spinal

nerves penetrate into the mesenchyme. At first, each

ventral ramus divides into dorsal and ventral branches,

but soon these branches unite to form named peripheral

nerves which supply extensor and flexor group of

muscles respectively.

Immediately after the above mentioned

rearrangement of nerves, they enter the limb buds and

establish an intimate contact with the differentiating

mesodermal condensations and this early contact

between the nerve and muscle cells is a prerequisite

for their complete functional differentiation.7

Over the years, two principal theories have

emerged concerning the directional growth of nerve

fibres-the neurotropism or chemotropism hypothesis

of Ramon y Cajal.8 and the principle of contact-

guidance of Weiss.9 The salient feature of chemotropism

is that axonal growth cones act as sensors to

concentration gradients of molecules in the environment

and grow up the gradient towards the source, i.e. the

target.

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There is no doubt, however that contact guidance

mechanisms operate in parallel with neurotropism.

Adhesion to the structures with which the growth cone

contacts also plays a role.

A group of cell surface receptors viz. neural cell

adhesion molecule (N-CAM) and L1 and the

Cadherins act as transcription factors which recognize

and bind to components of the extracellular matrix.

Thus, both cell-cell and cell-matrix interactions may

be involved in axonal pathfinding.10

Over or under expression of one or multiple

transcription factors as mentioned above have been

found to be responsible for the variations in the formation,

relation and distribution of the motor nerve fibers10.

The variations could arise from circulatory factors

at the time of fusion of the cords of brachial plexus.11

The variations in the formation of median nerve in

the arm bear remarkable clinical significance.

Considering these variations Rao advocated that the

clinicians and surgeons should be aware of such

variations while performing surgical procedure in this

region.12 Injury to such a variant nerve in the proximal

arm may lead to a galaxy of manifestations including

sensory, motor, vasomotor and trophic changes.3

The possible clinical implications of these variations

relating either to the surgical approach to the shoulder

joint and entrapment syndromes are important.13

Anomalies of axillary or brachial artery are

frequently related to unusual pattern of brachial plexus

and median nerve.14 However, in our case no abnormal

arterial pattern was detected.

References:

1. Williams PL, Bannister LH, Berry MM, et al - Gray’s

Anatomy. In: Nervous System. 38th ed. London Churchill

Livingstone, 1999; 1270.

2. Chauhan and Roy Communication between the median

and musculocutaneous nerve-a case report.journal of

the anatomical Society of India. 2002:52(1):72-5.

3. saeed and Rufai,A.A.-Median nerve and

musculocutaneous nerves:variant formation and

distribution. Clinical Anatomy.2003:16:453-7.

4. Satyanarayana N and  Guha R -Formation of median

nerve by four roots. J college of medical sciences

2008;vol.5,no.1:105-7.

5. Standring S, Ellis H, Healy JC, et al - Gray’s Anatomy.

In: General organisation and surface anatomy of the

upper limb.39th ed. Philadelphia Elsevier Churchill

Livingstone, 2005; 803-4.

6. Guha R and Palit S - A rare variation of anomalous

median nerve with absent musculocutaneous nerve and

high up division of brachial artery. J Interacad 2005;

9(3): 398-403.

7. Saddler TW - Langman’s Medical Embryology. In:

Muscular system. 10th ed. Philadelphia Lippincott

Williams & Wilkins, 2006; 146-7.

8. Ramon y Cajal S – Accion neurotropica de los epitelios.

Algunos detalles sobre el mecanismo genetico de las

ramificaciones nerviosas intraepiteliales sensitivas y

sensoriales. Trab Lab Invest Biol 1919; 17:65-8.

9.  Weiss P – Nerve patterns: the mechanics of nerve

growth. Growth (suppl 5) 1941; 163-203.

10. Williams PL, Bannister LH, Berry MM, et al - Gray’s

Anatomy. In: Embryology and development. 38th ed.

London Churchill Livingstone, 1999; 231-2.

11. Kosugi,K Mortia. T,Yamashita.H: Branching pattern

of the musculocutaneous nerve-Jikeakai Medical

journal.1986;33:63-71.

12. Rao PPV and Chaudhary SC - Communication of

musculocutaneous nerve with the median nerve. East

Afr Med J 2000; 77(9):498-503.

13. Venieratos D and Anagnostopoulou S – Classification

of communication between musculocutaneous and

median nerves. Clin Anat 1998; 11(5): 327-31.

14. Basar R, Aldur MM, Celik HH, et al- A connecting

branch between the musculocutaneouos nerve and the

median nerve. Morphologie 2000; 84(266): 25-7.

N. Satyanarayana et al. Unusual case of laryngeal foreign body: A case report

49



Figure No.-1.  Shows  formation of median nerve by three roots, two  from lateral cord of brachial plexus joining

individually with medial root of median nerve forming the median nerve trunk.

LC= Lateral Cord, R1= Root one, R2= Root two, R3= Root three, MN= Median nerve, MCN=

Musculocutaneous nerve, UN= Ulnar nerve, AA= Axillary artery, BA= Brachial artery, BB=Biceps Brachii,

CBM=Coracobrachialis Muscle.

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