Unusual morphological pattern and distribution of the ansa cervicalis: a case report.

Ansa cervicalis presents great anatomic variability regarding its origin and formation, the number of its roots and its distribution, as well. In the current case, we report an aberrancy in the form and distribution of ansa cervicalis' branches to the infrahyoid muscles and the sternocleidomastoid muscle, which is unique, since, to the best of our knowledge, a similar case has not been recorded in the literature. During regular dissection, we detected that the ansa cervicalis' loop, which was formed underneath the superior belly of the omohyoid muscle, provided a branch for the sternothyroid muscle, from which two recurrent rami were arisen. These two rami joined together forming an unusual triangular nerve formation. The neural trunk formed by the union of the aforementioned two rami perforated the inferior belly of the omohyoid muscle and afterwards was directed towards the ipsilateral sternocleidomastoid muscle. The awareness of such an unusual variability to the surgeons of the head and neck region would be of great importance, since it is crucial not to damage the ansa cervicalis or its branches in order to prevent any possible phonation disorders. Additionally, ansa cervicalis is proved to be extremely useful in the re-innervation of the larynx following paralysis of the recurrent laryngeal nerve.