Scalenus muscle and the C5 root of the brachial plexus: bilateral anatomical variation and its clinical significance.

Objective: To describe an anatomical variant wherein, bilaterally, the C5 ventral root passes anterior to the anterior scalene muscle.

Clinical implications: This and other variants in the anatomy of brachial plexus may complicate diagnosis of thoracic outlet syndrome, by producing unconventional signs and symptoms. Additionally, the passage of C5 ventral root anterior to the anterior scalene muscle, as in this case, may render the nerve root more susceptible to injury, including injury during manual therapy directed to this region.