Bilateral Accessory Clavicular Heads of Sternocleidomastoid Stenosing Supraclavicular Fossa in Human: Case Report

The sternocleidomastoid muscle (SCM) is an important landmark for many clinical procedures performed in the neck. Typically, the SCM consists of two heads of origin, sternal and clavicular. We came across bilateral accessory clavicular fibers of the SCM having extended attachment up to the middle third of the clavicle in an elderly cadaver. On the right side, the accessory fibers formed a distinct, separate belly in the form of cleidooccipital muscle. On the left side, four clavicular heads of SCM were observed, which were partially separated from each other. The presence of accessory clavicular fibers may stenose supraclavicular fossa. Additionally, the SCM with accessory clavicular fibers is not a reliable surface landmark and hence may pose difficulties in important procedures in the region such as central venous catheterization.