Duplicated posterior belly of digastric muscle and absence of omohyoid muscle: a case report and review of literature.

Purpose: We report a unique case of duplicated posterior belly of digastric muscle and absence of omohyoid muscle, review literatures and discuss its clinical importance.

Materials And Methods: An abnormal strip of muscle was found during the routine functional neck dissection in a 58-year-old man, who suffered from moderately differentiated squamous cell carcinoma of right tongue. We check the anatomical features and search for similar variations in the past literatures.

Results: The abnormal strip of muscle was attached to mastoid process, passed anteroinferiorly into the infrahyoid muscles. The muscle was as long as, but narrower than the posterior belly of the digastric muscle. So far, only one case of this anomaly was reported. Meanwhile, the omohyoid muscle was confirmed to be absent in the right neck of this patient.

Conclusions: To our knowledge, report of variations of both digastric muscle and omohyoid muscle, this variation mostly derives from abnormal development of the mesenchyme in the branchial arches. Attention should be paid to such variations, which might influence surgical procedures.