A complex scalenus muscle variant: Case report

During dissection in a first year dental gross anatomy laboratory, we identified an unusual, complex muscle variant in the left posterior triangle of an 87 year‐old, Caucasian female cadaver. This consisted of the left anterior scalene divided longitudinally into two approximately equal ‘heads', superficial and deep, with the fifth and sixth cervical nerve roots passing between them, along with a small but substantial muscle bundle passing between and attaching to portions of the anterior and middle scalene muscles. This extra muscle bundle passed antero‐medially from the middle of the anterior surface of the middle scalene, to attach inferiorly on the superficial aspect of the deep head of the anterior scalene. This ‘bridging’ muscle also passed anterior to and in contact with the middle trunk (C7) of the brachial plexus. The left subclavian artery was observed to pass as expected between the anterior scalene (both superficial and deep heads) and middle scalene insertions. Scalene muscle anatomy and neurovascular relationships on the right side were observed to be normal. Amidst the numerous reports of morphological variations in scalene muscles, particularly in association with the clinical anatomy of thoracic outlet syndrome, myofascial pain, and upper brachial plexopathies, we were unable to find any accounts of a similar complex scalene muscle variant. Most certainly, our specimen did not fit the accepted morphological descriptions of ‘scalenus anticus', scalenus minimus, or Sibson's muscle variants. Although we had no available clinical records, the muscular variations we described were arranged in configurations that other investigators have recognized as contributing to compression of brachial plexus roots associated with thoracic outlet syndrome. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .