|Year : 2015 | Volume
| Issue : 1 | Page : 43-45
Duplication in the formation of median nerve - a case report
Gyata Mehta1, Varsha Mokhasi2
1 Assistant Professor, Department of Anatomy, Vydehi Institute of Medical Sciences and Research Centre, Bangalore, Karnataka, India
2 Professor and Head, Department of Anatomy, Vydehi Institute of Medical Sciences and Research Centre, Bangalore, Karnataka, India
|Date of Web Publication||29-Nov-2019|
225/3, Golden Jubilee Complex, Near Command Hospital (AF), Old Airport Road, Bangalore - 560 007, Karnataka
Source of Support: None, Conflict of Interest: None
The median nerve is formed in the axilla by fusion of the two roots from the lateral and medial cords.The present case report describes an anomalous presentation of double formation of median nerve and its relation with axillary and brachial arteries. The median nerve was formed in two stages at different levels, first in the axilla and then in the upper arm by receiving double contribution from the lateral root of the lateral cord, which fuse with the medial root of the medial cord to form the median nerve. The formation took place medial to the axillary artery in the axilla and antero-medial to the brachial artery in the arm. Such anatomical variations and their relation with the arteries are important for the surgeons and anesthesiologists and of great academic interest to the anatomists.
Keywords: double formation, plexus, lateral cord, axilla
|How to cite this article:|
Mehta G, Mokhasi V. Duplication in the formation of median nerve - a case report. Natl J Clin Anat 2015;4:43-5
| Introduction|| |
The median nerve (MN) has two roots from the lateral (LC) (C5, 6, 7) and medial cords (MC) (C8T1), which embrace the third part of axillary artery and unite anterior or lateral to it. In contrast to the other terminal branches of the plexus, the MN is complex since it takes its origin by two large roots, it can be expected to contain fibers from each of the five spinal nerves regularly entering the plexus. Much has been written about the various anomalies of the MN but unusual formation by multiple roots though documented, is not very common. Such variations usually remain asymptomatic and are detected at the time of surgery, autopsy or cadaveric dissection. With the advent of newer diagnostic techniques like CT and MRI, anatomical variations have gained more clinical significance. Our study highlights an anomalous presentation of double formation of MN at different levels and its relation with axillary and brachial arteries.
| Case Report|| |
During the routine dissection of upper extremity for Ist year MBBS students, a variation was noted in a sixty year old male cadaver on the right side. The brachial plexus was dissected and exposed according to standard guidelines. Double formation of MN was observed on the right side. The first formation took place in the axilla by the fusion of lateral root of median nerve (LRM)(1) and medial root of median nerve (MRM). Here, the LRM(1) which was short and thin crossed the front of the axillary artery from lateral to medial side, to form the MN (a), medial to the third part of axillary artery. The MN (a) passed downwards, maintaining medial relation with third part of axillary artery and brachial artery. In the upper part of the arm, it received a second contribution from LRM (2) which was long and thick, from the LC that joined the MN (a) at a lower level, antero-medial to the brachial artery forming MN(b). Thus the MN was formed at two stages, first in the axilla and then in the upper arm, receiving the LRM from the LC twice. The relation was medial and antero-medial to the axillary artery and brachial artery respectively. [Figure 1].
|Figure 1: Showing the double formation of median nerve in the axilla and in the upper arm and its relation with axillary artery and brachial artery|
1-lateral root of median nerve(1); 2-medial root of median nerve; 3-median nerve(a); 4-lateral root of median nerve(2); 5-median nerve(b); 6-axillary artery; 7-brachial artery; 8- musculocutaneous nerve; 9-axillary vein; Single arrow - first formation of median nerve in axilla; Double arrow-second formation of median nerve in upper arm.
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On the left side, the formation of MN was normal by the fusion of LRM and MRM from the LC and MC respectively in the axilla, enclosing the third part of the axillary artery. No other anomaly was found.
| Discussion|| |
Previous studies have reported the formation of MN in two stages in 20% of cases. Other authors have also reported the formation of MN by three roots, two from the LC and one from the MC,,. Some studies have shown the formation of MN by four roots, with a contribution of three roots from the LC and one root from the MC. The third and fourth root from the LC arose from LRM and musculocutaneous nerve (MCN) respectively,. Although it is mentioned in literature that if LRM is small, the MCN connects with the MN in the arm .This results from the fact that majority of the MN fibers from the LC pass into the MCN and then re-join the MN at a lower level. Hence commonly the lower of the two roots joins the main trunk at a variable distance in the arm as seen in the present study and also by other workers,,,,. However it has been seen that both roots coming from the LC joined the MRM in the axilla and formed the MN. Such variations are commonly associated with communication between MCN and MN,. No such communication was noted in the present study.
Relation of MN with axillary artery is clinically significant as anomalous branches of LC crossing the artery anteriorly may cause compression symptoms producing ischemia. In the present study, the first formation of MN took place medial to the axillary artery and the second formation in the arm was found antero- medial to the brachial artery. Our study corresponded with the findings of the other authors,,,,. Formation of MN behind the third part of axillary artery also has been reported,. This change in relationship between cords of brachial plexus and axillary artery may be due to change in the source of subclavian artery from the usual 7th segmental artery which is between the LC and MC, to the 6th or 8th segmental artery which will cause medial or lateral displacements of cords in relation to the artery respectively. Awareness of such anomalies is important for surgeons operating in this area.
These anatomical variations can be explained embryologically. In human, the forelimb muscles develop from the mesenchyme of the paraxial mesoderm during the fifth week of embryonic life. The axon of spinal nerve grows distally to reach the limb bud mesenchyme. The peripheral process of the motor and sensory neurons grows in the mesenchyme in different directions. Once formed, any developmental differences would persist postnatally. As the guidance of the developing axons is regulated by expression of chemo attractants and chemo repellants in a highly coordinated site specific fashion, any alteration in signaling between mesenchymal cells and neuronal growth cones can lead to significant variation.
| Conclusions|| |
Knowledge of such variations is of paramount importance to surgeons and anesthesiologists during surgical exploration of axilla and arm region and during nerve block. It is of academic interest to the anatomists, and prior academic knowledge helps in better understanding and interpretation of such variations.
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