A rare case of bilateral supernumerary heads of sternocleidomastoid muscle and its clinical impact.

The sternocleidomastoid muscle (SCM) functions as a landmark for physicians such as anatomists, orthopaedic surgeons, neurosurgeons, and anaesthesiologists, who intervene in the minor supraclavicular fossa located at the base of the neck. The variability of SCM anatomy may cause complications while trying to access the vital elements that are located in the minor supraclavicular fossa. This study aims to present a case of supernumerary heads of the sternocleidomastoid muscle and to discuss its clinical significance. The cervical region of an elderly male cadaver was dissected and the findings were recorded and photographed. On both sides, the SCM muscle had an additional sternal head, and simultaneously there were three additional clavicular heads, four in total. These additional heads, the sternal and the clavicular, reduced the interval between them causing significant stenosis of the minor supraclavicular fossa. Sternocleidomastoid muscle variations with regard to the number of its heads are very rare in the literature, but this variation may cause severe complications. The minor supraclavicular fossa is important for anaesthesiologists because of the anterior central venous catheterization approach. Physicians should be aware of this anatomical variation in order to prevent complications.