Growth of the brachial nerve plexus with reference to topographical relation of the medianus nerve ansa with the thoracic wall and shoulder: a histologic study using human embryos and fetuses

Abstract

BackgroundThere is currently no information on positional changes in the brachial nerve plexus during prenatal growth. The subclavian-axillary artery passing through the medianus nerve ansa is considered a good landmark for evaluating the height of the plexus. Materials and MethodsWe used histological sections from 9 embryos and 17 fetuses (approximately 6-15 weeks of gestational age) to identify the height of the ansa by referring to the level of the rib and the glenohumeral joint. ResultsThe nerve ansa was usually (23 plexuses) observed at the level of the rst and/or second ribs. However, it was sometimes observed above the rst rib, at a distance equal to or more than an intercostal width (7 plexuses). In the latter group, the ansa was usually located below the glenohumeral joint. Thus, the joint was located higher than the rst rib, although the upper extremities were in the anatomical position for all specimens. The left-right difference in the height of the plexus corresponded to or was less than the width of the rst intercostal space. Despite the synchronized growth between the thorax and shoulder girdle, the brachial plexus showed a considerable variation in comparative height; the range corresponded to twice of an intercostal width. Whether the nerve plexus is located high or low is determined at an early developmental stage and is maintained during the later growth stages. ConclusionsThe high-positioned plexus might cause nerve injury at delivery, followed by a glenohumeral joint deformity because of the fragility without xation in the thorax.