Variations of the Brachial Plexus: A Study in Human Fetuses

Andrade LS

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OJHAS Vol. 18, Issue 1: (January-March 2019)

Original Article
Variations of the Brachial Plexus: A Study in Human Fetuses

Authors:
Lydia S. Andrade, Assistant Professor, Department of Anatomy, Kasturba Medical College, Manipal, MAHE, Manipal, Karnataka - 576104,
Ishita Singh, Undergraduate student, Kasturba Medical College, Manipal, MAHE, Manipal – 576104

Address for Correspondence
Dr. Lydia S. Andrade,
Assistant Professor, Department of Anatomy,
Kasturba Medical College, Manipal,
MAHE, Manipal,
Karnataka - 576104, India.
E-mail: lidibudy@gmail.com.

Citation
Andrade LS, Singh I. Variations of the Brachial Plexus: A Study in Human Fetuses. Online J Health Allied Scs. 2019;18(1):13. Available at URL: https://www.ojhas.org/issue69/2019-1-13.html

Submitted: Mar 2, 2019; Accepted: Apr 12, 2019; Published: Apr 30, 2019

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This work is licensed under a Creative Commons Attribution-No Derivative Works 2.5 India License

Abstract: Objectives: Brachial plexus, is a nerve plexus, that supplies the upper limb. Very few studies have been conducted in the fetus to know its pattern of variations. Therefore, this study aimed to identify the variations in the brachial plexus in human fetuses. Materials and method: Twenty-five formalin-fixed human fetuses were dissected bilaterally and the variations in the roots, trunks, cords and branches were identified. Results: Out of the fifty brachial plexuses studied, thirty-five plexuses were normal and fifteen showed variations. Among the fifteen variant plexuses, more number of variations were seen in the median nerve branch of the lateral cord of brachial plexus. These variations in the fetuses show that the adult pattern of variations are pre-determined in the embryological life. Conclusion: Therefore, these variations are of clinical importance for the clinicians and surgeons performing surgeries in the region of the axilla and in the upper limb.
Key Words: Brachial plexus, Cords, Fetus, Roots, Median nerve

Introduction:

The brachial plexus is a somatic plexus formed by the anterior primary rami of C5 to C8 and T1. A limited contribution is also given by C4 and T2. The plexus originates in the neck, passes lateral and inferior to the first rib, and enters the axilla. The parts of the brachial plexus, from medial to lateral are, roots, trunks, divisions, and cords. All major nerves that innervate the upper limb originate from the brachial plexus, mostly from the cords. The brachial plexus would be called as pre-fixed if there is excessive contribution from C4 and the contribution from T1 is suppressed. Similarly, the brachial plexus would be called post-fixed when there is more contribution from T2 and least contribution from C5. A complex interchange of branches, before the main nerves of the upper limb are formed, produces its trunks, divisions, and cords [1].

A lot many studies regarding the variations in brachial plexus have been conducted on adult cadavers [2-5]. However, there is a paucity in the fetal study. Embryologically, the formation of brachial plexus is completed by the 13^th week of gestation [6, 7]. Thereafter, there would only be growth along with the lengthening of the body of the fetus. Therefore, this project aims at viewing any morphological and/or anatomical deviations from normal by dissecting a total of 25 fetuses from the second and third trimesters.

Objectives

There is seen to be a considerable amount of variations in the brachial plexus, and a dissection of a total of 25 fetuses is to be made to come up with a conclusive result. The variations thus seen will be photographed. The objective here, is to determine the possible variations occurring in the brachial plexuses of developing fetuses. The variations due to clinical mishandling and/or accidents are not included.

Materials and Methods

Twenty-five spontaneously aborted fetuses, irrespective of their sex, belonging to the second and third trimesters, were procured from the Department of Obstetrics and Gynecology, KMC, Manipal. These fetuses were stored in 10% formalin solution. The fetuses with any visible abnormalities/malformations were excluded from this study. Further study was conducted in the Department of Anatomy, KMC, Manipal. The dissection was carried out bilaterally to observe the possible variations in the supraclavicular and infraclavicular parts of brachial plexus. To achieve this, an S-shaped incision was made along the posterior border of sternocleidomastoid muscle until the upper border of clavicle to the coracoid process and then down into the deltopectoral groove. The scalenus anterior muscle acted as a guide, to identify the roots and trunks of brachial plexus. The trunks and divisions were traced laterally up to the clavicle. Further, the clavicle was partitioned with a bone cutter to observe the possible variations in the infraclavicular part of brachial plexus (cords and branches) in the axilla. The variations were photographed. The entire study period lasted for eight months.

Results

Out of the fifty brachial plexuses studied, variations were observed in fifteen brachial plexuses (30%).

For reference purposes, a picture of a standard brachial plexus of the right side is as shown in Fig 1. The variations thus found are tabulated (Table 1).

Table 1. Variations of brachial plexus
Variation	Age	Male	Female
Upper trunk and lower trunk of brachial plexus (fig. 2)	3^rd trimester	1	1
Upper trunk and lower trunk of brachial plexus (fig. 2)	2^nd trimester	----	----
Prefixed brachial plexus (fig. 3)	3^rd trimester	----	----
Prefixed brachial plexus (fig. 3)	2^nd trimester	1	----
Two lateral roots of the median nerve originating from the lateral cord (fig. 4)	3^rd trimester	3	1
	2^nd trimester	1	1
Median nerve formation with multiple roots (fig. 5)	3^rd trimester	1	----
Median nerve formation with multiple roots (fig. 5)	2^nd trimester	----	----
Low formation of median nerve (fig. 6)	3^rd trimester	----	----
Low formation of median nerve (fig. 6)	2^nd trimester	1	----
Communication between median & musculocutaneous nerves (fig. 7)	3^rd trimester	3	----
	2^nd trimester	----	1

	Figure 1. Normal right brachial plexus

Figure 2. Right Brachial plexus showing two trunks	Figure 3. Left pre-fixed brachial plexus

Figure 4. Additional lateral root of median nerve from lateral cord	Figure 5. Median nerve formation with multiple roots

Figure 6. Low formation of median nerve	Figure 7. Communication between median & musculocutaneous nerves

Discussion

Brachial plexus variations have been widely studied in the adult cadavers. A few studies have also been conducted in the fetal cadavers. Variations in the roots of brachial plexus – A study conducted by Lee et al on 77 adult cadavers, showed that 21.5% had pre-fixed brachial plexus and only one case showed contribution from both C4 and T2 [8]. Out of the 200 brachial plexuses studied by Uysal on fetuses, 25.2% were pre-fixed and only 2.5% were post-fixed. In the present study, pre-fixed brachial plexus was observed only in a single brachial plexus (fig. 3) [7].

Variations in the trunks of brachial plexus – Normally, the there are three trunks, namely, upper, middle and lower trunks. The upper trunk is formed by the union of C5 and C6 roots, the C7 continues as the middle trunk and C8 and T1 forms the lower trunk. Numerous authors have described variations in the trunks of brachial plexus. In a study conducted by Uysal et al, in 1% case, the upper trunk was formed by C4 and C5 [7]. However, in the present study, no such variation was observed. The number of trunks varied from 2 to 4. Two trunks, namely upper trunk formed by the fusion of C5, C6 and C7 roots and lower trunk formed by C8 and T1, was observed by Matejcik, Aragao et al. and Nayak et al. In the present study, similar variations were observed in 2 brachial plexuses [9-11]. Interestingly, Aragao et al., also mentioned that in 2.5% brachial plexuses, there were four trunks. In the present study no such finding was observed.

Variations in the cords of the brachial plexus – Several cord variations have been revealed by the previous authors. In a study conducted by Kerr et al., only 4% cases showed the formation of lateral cord. Medial and posterior cords were identified in all the cases [12]. In the present study, all the cords and their formation was recorded as per the standard text book.

Variations in the distal branches of brachial plexus – Among the branches of brachial plexus, highest number of variations were found in the median nerve. Median nerve formed from three roots is the most widely found variation [13, 14, 7]. In the present study, similar variation was observed (2 lateral roots from the lateral cord and 1 medial root from the medial cord) in 6 brachial plexuses (fig. 4). A single case in the present study also found the formation of median nerve from multiple roots (fig. 5). More distal formation of median nerve was observed by Uysal et al., in about 8.5% cases [7]. In the present study, a single brachial plexus showed a similar finding (fig. 6). A few authors have also shown a communicating branch between median and musculocutaneous nerves [7, 12]. In the present study, a similar communication between median and musculocutaneous nerves was observed in 4 brachial plexuses (fig. 7).

Conclusion

The purpose is supposed to be a self-investigation, documentation and deeper understanding of the combinations of converging and diverging patterns of the brachial plexus. The knowledge of these variations would help surgeons to perform surgeries better in the cervical and axillary regions. The presence of all possible anatomical variations can also explain certain abnormal symptoms and would facilitate the localization necessary for diagnosis and treatment of those symptoms. Due to abnormal communications, the defined dermatomes may be blurred, and the patient may experience anaesthesia/pain in a different dermatome. Similarly, seemingly anomalous cases can be better diagnosed by knowing any possible occurrences of variations. Thus, a fair amount of clinical applications is also possible. In some cases, a worthy post mortem explanation may also be offered for the cause of abortion.

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