VCOM Louisiana Research Day Program Book 2024

Clinical Research

26 ANALYSIS OF CADAVERIC BRACHIAL PLEXUS VARIATIONS

Nouraan Sadiq, BS; Patrick Przybylo, BS; Rebecca Peters, MS; Cameron Driskell, BS; and Savannah Newell, PhD; VCOM-Louisiana

Background: The brachial plexus consists of a system nerves that are essential in proper functioning and control of the upper extremities. In its typical arrangement, it consists of a union of nerve fibers originating from the anterior rami of C5-C8 and T1. Variations in the arrangement of the brachial plexus can be traced back to its development embryologically from neural crest cells through discrepancies in signaling between neural growth cones and mesenchymal cells that are part of axonal growth regulation. It is essential to be aware of these variations to avoid iatrogenic injury regarding this area during surgical procedures such as radical neck dissection. In addition, variations in the brachial plexus can greatly affect the treatment strategies regarding this area, and alter the risks for the development of different conditions such as thoracic outlet syndrome. Since brachial plexus development is related to neural crest cell migration and somite migration, brachial plexus variation can also affect the distribution of dermatomes, and the subsequent clinical evaluation of it. Objective: The purpose of this research study was to identify and document the different variations of the roots, divisions, trunks, cords, and branches of the brachial plexus. Methods: The brachial plexuses of thirty racially diverse adult cadavers of different sexes were bilaterally examined for variations. The corresponding plexuses were sketched and those with variations were noted and photographed by multiple students. The variations documented were further classified whether they affected the infraclavicular or supraclavicular portions

of the brachial plexus, and subsequent structures in the photographs were labeled. The cadavers were obtained from the UT Southwestern Body Program to be used in the anatomical educational curriculum at VCOM – Louisiana. Additional information regarding cause of death for each specimen was also provided along with age. The cadavers were systemically dissected from the roots of the brachial plexus along the cervical and upper thoracic vertebrae of the neck to the wrist of the arm with all of the underlying nerve connections in the axilla and antecubital fossa exposed. The position of additional structures such as the axillary artery and subclavian vein around the brachial plexus were noted as well. Results: Out of the 60 arms we examined we found a couple common variations in the infraclavicular and supraclavicular portions of the brachial plexus. The most frequently encountered variations found in the supraclavicular portion included suprascapular nerve origination at the C5 root (n = 10, 16.7%), T2 contribution to the inferior trunk (n = 4, 6.7%), C7 contribution to the superior rather than middle trunk (n = 2, 3.3%), independent origination of the suprascapular nerve from C5 and C6 respectively before seemingly joining the superior trunk (n = 2, 3.3%), lateral cord with inferior trunk contributions (n = 2, 3.3%), and C4 contributions to the superior trunk (n = 2, 3.3%). The most frequently encountered variations found in the infraclavicular region of the brachial plexus included distal median nerve formation from the axilla (n = 6, 10%), multiple lateral cord contributions to the median nerve (n = 33, 55%), and abnormal cord contributions to the ulnar nerve including the lateral cord (n = 12,

20%) and posterior cord (n = 1, 1.7%). Other variations found included merging of the median nerve with the musculocutaneous nerve (n = 3, 5%), and lateral and medial cord joining (n = 1, 1.7%). The results highlight the commonality of the brachial plexus variations as approximately 75% of the cadavers studied had an identifiable variation. Conclusions: Although more research is needed, some common variations in the brachial plexus were identified and subsequently analyzed in this study. The most frequent variations were found in the infraclavicular portion of the brachial plexus. The exact causes of brachial plexus variations are still under further study, but possible reasons are related to the disruption of axonal development and neural crest cell migration signaling. In addition, variations in brachial plexus configurations can alter the development of other nearby structures such as the axillary artery, and cause further anatomical variations. Dermatome distributions can be affected by brachial plexus variation due to alterations in embryological somite migration, and affect their clinical interpretations. The brachial plexus often is subjected to injury from various causes such as motor vehicle accidents, stabbings, gunshot wounds, or birth complications resulting in conditions such as Erb or Klumpke palsies, etc. Given how common injury to the brachial plexus is, it is important for physicians to be aware of common anatomical variations to better plan treatment and avoid iatrogenic injuries. The knowledge and documentation of these variations can better equip surgeons when performing procedures such as radical neck dissection and nerve repair in this area.

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