Introduction
This topic covers the infrahyoid region, the part of the anterior neck between the hyoid bone and the sternum. It contains the four infrahyoid (strap) muscles, the thyroid and parathyroid glands, the larynx, the trachea and the upper oesophagus. It is the surgical field for thyroid operations and an important site for neck masses.
Boundaries and layers
The region is bounded above by the body of the hyoid bone, below by the jugular notch of the sternum and the clavicles, and laterally by the medial borders of the sternocleidomastoid muscles. Superficially, it is covered by the platysma and the superficial fascia, which contain the anterior jugular veins and small cutaneous nerves. The strap muscles lie under the investing layer of the deep cervical fascia, and the visceral (pretracheal) layer covers the thyroid, the larynx and the trachea.
The infrahyoid muscles
The omohyoid has two bellies joined by an intermediate tendon, which is held against the clavicle by a fascial sling. All four muscles act together during swallowing, when the hyoid and larynx are pulled down after being raised.