Bilateral clavicular attachment of omohyoid muscle

Radiological assessment of the dissection area in supraomohyoid neck dissection

PURPOSE

The current supraomohyoid neck dissection (SOHND) is performed above the omohyoid muscle to dissect levels I, II, and III in the levels of cervical lymph nodes. However, the anatomical boundary between levels III and IV is the inferior border of the cricoid cartilage. We investigated the anatomical relationship between the omohyoid muscle and cricoid cartilage using contrast-enhanced CT (CE-CT) images to assess the validity of the current SOHND.

METHODS

CE-CT images of the head and neck regions in patients were reviewed. The patients were divided into two groups: "malignant tumors" and "others". The vertebral levels corresponding to the positions of anatomical structures such as the intersection of the omohyoid muscle and internal jugular vein (OM-IJ), and the inferior border of the cricoid cartilage (CC), were recorded.

RESULTS

The OM-IJ was located around the seventh cervical to the first thoracic vertebra. There was a significant difference between the malignant tumor and others groups in females (p = 0.036). The CC was located around the sixth to seventh cervical vertebrae. There was a significant sex difference in each group (malignant tumor: p < 0.0001; others: p = 0.008). Both sexes tended to have lower OM-IJ than CC, and females had significantly lower OM-IJ than males.

CONCLUSION

This study provides clear anatomical evidence showing the difference between the SOHND dissection area and levels I, II, and III. It could be considered that in most cases SOHND invades level IV, not just levels I, II, and III, especially in female patients.

The previously undescribed variant of the thyrohyoid muscle and its potential impact on surgical procedures

The thyrohyoid muscle belongs to the infrahyoid group located in the carotid triangle. It normally originates from thyroid cartilage and inserts into hyoid bone. Quite often, it is continuous with the sternohyoid muscle. Furthermore, there are variants that have their origin in the cricoid cartilage only, however, this occurs very rarely. During anatomical dissection, a two-headed variant of this muscle was found. One head had its origin in the cricoid cartilage and the other in the thyroid cartilage. This variant of thyrohyoid had not been previously described in the available literature. Therefore, we believe that it may be referred to as the cricothyrohyoid muscle. As the thyrohyoideus is often used as a landmark during surgical procedures in the prelaryngeal area and as a muscle graft, a thorough knowledge of its anatomy and variation is extremely important. We speculate that the two-headed version of this muscle may be problematic during surgical procedures in this region, however, it may also provide more options as a muscular graft.

An anomalous muscle clinging around the inferior belly of omohyoid muscle

Sternohyoid, sternothyroid, omohyoid and thyrohyoid muscles belong to a group of muscles called infrahyoid muscles. A few variations of these muscles and additional muscles in this area have been reported. We report an anomalous muscle in this area. The anomalous muscle took its origin from the posterior surface of the manubrium sterni and was inserted to the posterior surface of the clavicle. This muscle was 6 cm long and interestingly, it made a loop, which was clinging on to the inferior belly of omohyoid posteriorly, superiorly and anteriorly. The muscle was situated between the lower end of sternocleidomastoid and the carotid sheath. It was supplied by ansa cervicalis. Knowledge of this muscle could be useful in surgeries like removal of cervical rib, and cervical lymph node clearance. Hypertrophy of this muscle might compress the internal jugular vein.