Sternocleidomastoid muscle additionally innervated by the facial nerve: case report and review of the literature.

An aberrant nerve branch from the facial nerve, additionally to the accessory nerve and cervical rami C2 and C3, was observed innervating the sternocleidomastoid (SCM) muscle in a 75-year-old male cadaver. We consider that the anomaly occurred as the result of a fusion of the muscular compartment from the digastric and SCM muscles during development. The aberrant innervation may be the source of the misinterpretation of electromyographic findings.