Additional lateral root of the Ulnar and Median nerves - Case study ●
Dorian Wolff - Amandine Labarthe
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Coordinator: Dr. Kory-Mercea Bogdan
UMF Cluj – Department of Anatomy, Cluj-Napoca, Romania
Introduction: ● ●
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Brachial plexus Formation: Ventral rami of the lower cervical and upper thoracic nerve roots between C5 and T1. Course: Neck, axilla and upper part of the arm. Territories: Cutaneous and muscular innervation of the upper limb.
Brachial Plexus:
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The five anterior rami of the spinal nerves merge to form three trunks: superior (C5-C6), middle (C7), inferior (C8T1).
Brachial Plexus:
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Each of these trunks splits in two branches, one anterior, and one posterior.
Brachial Plexus: ●
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Anterior divisions of the upper and middle trunks will form the lateral cord. The three posterior divisions will regroup to form the posterior cord (which is posterior to the axillary artery). Anterior division of the lower trunk will form the medial chord.
1) Lateral cord - Lateral root of the median nerve -Musculocutaneous nerve 2) Medial cord: - Medial root of the median nerve - Ulnar nerve -Medial brachial and antebrachial nerves 3) Posterior cord: -Radial nerve -Axillary nerve
Divisions of cords:
Objectives: ●
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This study presents a case of an additional lateral root of the Ulnar and Median nerves. It could provide important informations about the variations of these nerves and their origins, in order to avoid injuries and possible impairment of a patient during surgical procedures of axillary region.
Materials and methods: ● ●
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Adult male cadaver Dissected by classical dissection in the Department of Anatomy, UMF Cluj-Napoca, Romania. The entire upper arm and the axillary region were dissected carefully. The variations from the usual pattern were noted.
Results: ●
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A lateral root of the ulnar nerve, which originated from the lateral cord, was found. Usually the lateral cord only gives three branches: lateral pectoral nerve, lateral root of median nerve and musculocutaneous nerve. The fourth branch of the lateral cord splits in two, posteriorly to the origin of median nerve.
Results: ●
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One of the two branches courses to the medial nerve -> Lateral origin of the right ulnar nerve. The branch that made an anastomosis with the median nerves forms a third origin of the right median nerve (second lateral origin). The additional branch : approximately 3.5 cm long.
Fig. 1: Right Arm: View of the Lateral Root of the Ulnar Nerve - Closeup ●
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The branch coming from the lateral cord, passes under the medial root of Median nerve. Divides in two branches, one going back to the median nerve, and the other forming the lateral root of the ulnar nerve.
Fig. 1: Right Arm: View of the Lateral Root of the Ulnar Nerve ●
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Musculocutaneous can be seen.
nerve
The insertion of the lateral root of ulnar nerve is in its lateral side. The third root of the median nerve joins him between the two other roots. The fourth branch of lateral cord runs inferiorly to medial root of the median nerve.
Drawing of the variation:
Results:
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Apart from the fourth branch emerging from the lateral chord, the rest of the brachial plexus follows the regular pattern, and no other variation can be observed.
Discussion: ●
The fourth branch divides itself in two parts:
One towards nerve.
median
One towards ulnar nerve. ●
The anatomical variant of this brachial plexus consists in the presence of the fourth abnormal branch.
Discussion ●
On a plexus:
usual
This fourth branch does not exist. The ulnar nerve does not have any lateral origin.
Discussion: ●
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There wasn't any living subject bearing this anomaly available for our study, We cannot be sure about the consequences that it could have.
possible
functional
We are not yet in possession of any method that could permit us to find out what those consequences would be on a living subject.
Discussion: ●
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We do know that both the nerves Ulnar and Median carry motor and cutaneous sensitive functions, especially in the forearm and the hand. Both muscular and sensitive functions of the territories innervated by the Ulnar and Median nerves could be altered in one or another way.
Discussion: ●
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Most common brachial plexus variation are at root, but they can also be found at division of a trunk, formation of a cord, or at the root of a nerve. These variations could be damaged during the neck dissection or during axillary surgery, thus it's important for surgeons and anatomists to know about their presence.
Discussion: ●
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Anatomic variants often happen in the brachial plexus. (according to Valeria Paula et al. - Brachial plexus variation in its formation and main branches. Acta Cir. Bras. 2003; 18:5.). Errors of migration of nerve cells axons are corrected distally in the arm, thus the brachial plexus often carries anatomical variations.
Discussion: ●
According to F.K. Fuss (Fuss FK. Acta Anatomica. 134(3):199-205) a lateral branch of the ulnar nerve is normal, and is not an anatomic particularity but is more of a variant as it was found in 56% of the brachial plexuses he investigated.
Discussion: ●
According to T.W. Sadler (Langmans Medical Embryology. 9th edition, 2004, Luppincott Williams & Wilkins, 202-206) during the formation of the Brachial Plexus, the nerve cells remain with their original muscles as they migrate.
Hypothesis: ●
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Based on the embryologic argument: Every muscle bud migrates, preserving it's own innervation. The nervous fibers may eventually group differently from the general pattern, but every muscle preserves the fibers coming from a certain neuromere. It could mean that the median nerve has a smaller than usual muscular territory and the ulnar nerve a bigger one.
Hypothesis: ●
Previous hypothesis can also be considered about the sensitive territories of the two nerves:
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The ulnar nerve would have a greater territory.
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The median nerve would have a smaller territory.
Conclusions: ●
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We have to pay particular attention to this zone in case of injury (accidental or surgical) of the axillary region. The reason: during the surgery of this zone, the abnormal roots of these nerves can be injured. Furthermore, there is no exterior sign that could signal the presence of this variation, so when working on the axillary region, we can't be sure if the brachial plexus follows the regular pattern.
