Bilateral anatomic variation in the relation of the upper trunk of the brachial plexus to the anterior scalene muscle.

The brachial plexus represents a field of many anatomical variations with impor- tant clinical implications, especially in the diagnosis and treatment of the thoracic outlet syndrome (TOS). The case described in this paper presented a novel bilateral variation in the relation of the upper trunk of the brachial plexus to the anterior scalene muscle. The ventral rami of the C5 and C6 spinal nerves perforated the anterior scalene muscle simultaneously through a common opening, and joined to form the upper trunk. Previous literature reports described variations of the brachial plexus and the scalene muscles, as well as the embryological basis for their presence. The case reported herein helps to improve the comprehension of the TOS, as well as the diagnostic and therapeutical approach to this syndrome.