Variation in the Formation and Branching Pattern of Brachial Plexus in the Human Foetuses: A Morphometric Cross-sectional Study

Introduction: The brachial plexus is a variable nerve plexus in its formation and branching pattern. Variations in the brachial plexus are not uncommon, and its area of supply and associations with other adjacent anatomical structures require clinical and surgical attention. Aim: To find out any anatomical variations in the formation and branching pattern of the brachial plexus in human foetuses. Materials and Methods: A morphometric prospective observational study was conducted from January 2020 to July 2022, on 30 stillborn or Intrauterine Dead (IUD) human foetuses were taken in the study. Gestation age from 28 to 40 weeks of gestation were included in the study, while those with gross anomalies or morphological anomalies of the cranium and vertebral column were excluded. The dissection includes vertical midline incision of the skin from the external occipital protuberance to the lower limit of the thoracic vertebra (T12). The skin was cut in the midline and reflected laterally. All superficial and deep muscles of the neck were dissect out to clear the cervical and thoracic parts of the vertebral column. The vertebral column was cut and opened to visualise the spinal cord and spinal nerves. Based on gestational age, the foetuses were divided into three groups: four in the first group (28-31 weeks), twelve in the second group (32-35 weeks), and fourteen in the third group (36-40 weeks) were divided for descriptive purposes. The gender of foetuses was determined based on the external genitalia. Results: A total of 60 brachial plexuses were dissected, of which 49 (81.66%) had the usual anatomical formation of the trunks: the upper trunk formed by C5 and C6 roots, the middle trunk by the C7 root, and the lower trunk by the C8 and T1 roots. Eleven (18.34%) plexuses presented variations in trunk formation. Specifically, 8 (13.3%) brachial plexuses were of the prefix type, where the upper trunk was formed by the C5 and C6 roots with an additional contribution from the C4 root; there was inter-branch communication between C6 and C7 in one (1.7%) case; the middle and lower trunks united by C7, C8, and T1 roots formed the lower trunk in another (1.7%) case, and finally, one (1.7%) case exhibited the post-fix type. Conclusion: In this study, out of the 30 foetuses examined, 11 showed variations, which is not uncommon. The prefix type of brachial plexus is quite common among the possible variations, although anatomists and neurosurgeons cannot ignore the possibility of other variations, like post-fix type or communication between the roots of the brachial plexuses.