Unusual origin of the omohyoid muscle

Ultrasonographic measurements of the omohyoid muscle during shoulder muscles contraction

BACKGROUND

The main function of the omohyoid muscle is to depress and withdraw the hyoid bone. This is an integral part of the swallowing process facilitating hyoid stabilization for tongue movement. Although the muscle is inferiorly attached to the scapula bone, its function during shoulder or scapula muscles contraction has yet not been studied.

AIM

To investigate whether changes occur in omohyoid muscle morphology during shoulder muscles contraction.

METHODS

The study included 40 healthy subjects (20 males and 20 females, Mean age: 25.68 (± 2.90) years) examined via diagnostic ultrasound. Omohyoid muscle morphology measurements (thickness and cross-sectional area) during different shoulder position (0°, 90° abduction and elevation) in rest and during isomteric contraction were evaluated.

RESULTS

The omohyoid muscle was activated when the shoulder was isometrically abducted at 90° abduction. Thickness and the cross-sectional area of the lower belly increased during contractions at 90° abduction compared with a resting position at 90° (p value < 0.01). No changes occurred at 0° isometric abduction. The CSA of the muscle was found to be significantly larger (p < 0.001) during contraction at 90° abduction compared with contraction at 0° abduction.

CONCLUSION

Omohyoid muscle was most contracted during abduction position with abduction shoulder muscles isometric contraction. Changes of the scapula position might influence omohyoid muscle function.

Unusual muscle of the anterior neck: cadaveric findings with surgical applications

The omohyoid muscle typically has an inferior belly originating from the superior border of the scapula, and then passes deep to the sternocleidomastoid muscle where its superior belly passes almost vertically upward next to the lateral border of sternohyoid to attach to the inferior border of the body of the hyoid bone lateral to the insertion of sternohyoid. Herein, we report an unusual variant of the omohyoid and sternohyoid muscles. As the omohyoid muscle is commonly used as a surgical landmark during neck dissections, knowledge of its variations such as the one described in the current report is important to surgeons.

Unusual morphology of the superior belly of omohyoid muscle

Though anomalies of the superior belly of the omohyoid have been described in medical literature, absence of superior belly of omohyoid is rarely reported. Herein, we report a rare case of unilateral absence of muscular part of superior belly of omohyoid. During laboratory dissections for medical undergraduate students, unusual morphology of the superior belly of the omohyoid muscle has been observed in formalin embalmed male cadaver of South Indian origin. The muscular part of the superior belly of the omohyoid was completely absent. The inferior belly originated normally from the upper border of scapula, and continued with a fibrous tendon which ran vertically lateral to sternohyoid muscle and finally attached to the lower border of the body of hyoid bone. The fibrous tendon was about 1 mm thick and received a nerve supply form the superior root of the ansa cervicalis. As omohyoid mucle is used to achieve the reconstruction of the laryngeal muscles and bowed vocal folds, the knowledge of the possible anomalies of the omohyoid muscle is important during neck surgeries.

Variation of the infrahyoid muscle: duplicated omohyoid and appearance of the levator glandulae thyroideae muscles

The embryologic origin of the omohyoid muscle is different from that of the other neck muscles. A number of variations such as the absence of muscle, variable sites of origin and insertion, and multiple bellies have been reported. However, variations in the inferior belly of the omohyoid muscle are rare. There have been no reports of the combined occurrence of the omohyoid muscle variation with the appearance of the levator glandulase thyroideae muscle. Routine dissection of a 51- year-old female cadaver revealed a duplicated omohyoid muscle and the appearance of the levator glandulae thyroideae muscle. In this case, the two inferior bellies of the omohyoid muscle were found to originate inferiorly from the superior border of the scapula. One of the inferior bellies generally continued to the superior belly with the tendinous intersection. The other inferior belly continued into the sternohyoid muscle without the tendinous intersection. In this case, the levator glandulae thyroideae muscle appeared on the left side, which attached from the upper border of the thyroid gland to the inferior border of the thyroid cartilage. These variations are significant for clinicians during endoscopic diagnosis and surgery because of the arterial and nervous damage due to iatrogenic injuries. The embryologic origins of the omohyoid and levator glandulae thyroideae muscles may be similar based on the descriptions in the relevant literature.

Pseudodysphagia due to omohyoid muscle syndrome

Omohyoid muscle syndrome (OMS) is a rare clinical condition that has the pathognomonic feature of the appearance of a lateral neck mass when swallowing due to dysfunction of the omohyoid muscle (OH). We present two cases of typical OMS with electrophysiologic and dynamic imaging studies. The study results indicate that OMS is caused mainly by the loosening of the fascial attachment to the intermediate tendon of the OH. The characteristic clinical features and pathomechanism underlying OMS are also discussed.

A study of anatomical variability of the omohyoid muscle and its clinical relevance

OBJECTIVE

The omohyoid muscle is a long, thin muscle consisting of superior and inferior bellies and an intermediate tendon, which runs obliquely in the lateral cervical region. The omohyoid is important in neck dissections because it is the surgical landmark for level III and IV lymph node metastases.

METHODS

In the present study, the anterior and posterior triangle of the neck was dissected in 35 male cadavers and observed for variations in the omohyoid bilaterally. Observations were focused on variations in number, attachments, and position of omohyoid.

RESULTS

Among the 35 cadavers studied, double omohyoid was present in one cadaver, inferior belly originated from the clavicle in three cadavers, superior belly merged with the sternohyoid in two cadavers, and the omohyoid received additional slips from the sternum in one cadaver. Standard attachment and position of the omohyoid was observed in the remaining cadavers.

CONCLUSION

Variations of this muscle are important because of its close relation to the large vessels and brachial plexus. Because of the direct adhesion of the intermediate tendon to the anterior wall of the internal jugular vein and its connection with it through a thin lamina of the pretracheal layer of the cervical fascia, the contraction of the omohyoid muscle has a direct effect on the lumen of this vessel.

An unusual variation of the omohyoid muscle and review of literature

The omohyoid muscle is important in radical neck dissection, as it is a landmark for this operation. Because it divides the anterior and posterior cervical triangles into smaller triangles and its particular relationship to the large cervical vessels, the presence of an anatomical variation of the omohyoid muscle is important. An unfamiliar muscle was found in the left anterior cervical region of a 57-year-old male cadaver. It was attached at its caudal end to the clavicle and coursed upward to the hyoid bone and a normal omohyoid muscle with its intermediate tendon was lateral to this muscle. Both the muscles joined together near the hyoid bone and both muscles attached to the hyoid bone with the same tendon. According to its origin and insertion, the unfamiliar muscle was considered to be the cleido-hyoideus muscle. In our case report, a variant of infrahyoid muscles is presented. Such an association constitutes an exceedingly rare condition.