Anatomical variations in the Ansa cervicalis and innervation of infrahyoid muscles.

ABSTRACT

Background: – Infrahyoid muscles are supplied by the ansa cervicalis. The present study aimed to study the variations in the ansa cervicalis and the innervation of infrahyoid muscles. Methods: The study was conducted on 40 cadaveric hemi-necks. Results: Out of the 40 hemi-necks, high level of ansa cervicalis was observed in 2 hemi-necks, intermediate level of ansa was observed in 35 hemi-necks and low level of ansa was observed in 3 hemi-necks. Additionally, dual ansa with absence of inferior root was seen in 4 hemi-necks, dual ansa with absence of inferior root and inter-communication between C2 and C3 was seen in 2 hemi-necks, common trunk supplying all infrahyoid muscles including superior belly of omohyoid was seen in 2 hemi-necks, nerve to inferior belly of omohyoid from inferior root was seen on 1 side. In one specimen unilaterally, superior belly of omohyoid was innervated by a branch from hypoglossal nerve, two superior roots arising from hypoglossal nerve and the inferior root formed only by C3 was seen in the same specimen. Discussion: The knowledge of the possible variations of ansa in relation to the great vessels of the neck prevents the inadvertent injury to those vessels. Any injury can result to phonation disability in professional voice users. In case of infrahyoid muscles palsy, patients have no serious voice problems in their normal speech but the pitch of their voice and also prosody in their singing are lost dramatically. Conclusion: These variations are of clinical importance for the reconstructive surgeries which involve the infrahyoid muscles.