A unilateral sternopharyngeal branch of the sternocleidomastoid muscle in an aged Caucasian male: a unique cadaveric report

The sternocleidomastoid muscle (SCM) consists of a sternal and a clavicular head which merge together and inserts distally posterolateral on the mastoid process and superior nuchal line, hence separating the anterior from the posterior triangle of the neck. Many types of structural variations in SCM have already been reported before. A unique variation of this muscle was discovered in an aged Caucasian male cadaver during an anatomical dissection at the Paracelsus Medical University in Nuremberg, Germany.This study reports a right unilateral accessory muscular branch at the sternal head of the SCM which formed a tendon on the level of omohyoid muscle before dividing into anterior and posterior fascicles. The posterior fascicle attached to the external carotid artery at the site where a common trunk for lingual and facial artery branched off, drawing external carotid artery inferiorly to build an inferior loop, whereas the anterior fascicle passed further superior and broadened to form a muscular belly. This superior muscular belly extended to the posterior and lateral side of the pharynx to ultimately merge into the superior constrictor pharyngeal muscle. Such anatomical variation has never been reported before.Therefore, we propose the nomenclature of this variational structure as a sternopharyngeal branch of the SCM. This report helps not only to inform the clinicians regarding the possible variation of this muscle during surgical procedures or radiological diagnostics but also encourage developmental researches in the future