The larynx is a midline structure at the level of C3 through C6 that connects the pharynx to the trachea. Its major functions include respiration, phonation, and swallowing. It is comprised of a cartilaginous skeleton, muscles, mucosal lining, ligaments, and membranes.[1]

The thyrohyoid membrane is one of the extrinsic membranes that compose the larynx. It is a broad fibro-elastic layer named for its attachments as it attaches the upper border of the thyroid cartilage to the hyoid bone. The thicker median section of the membrane is the thyrohyoid ligament. It attaches the superior thyroid notch/laryngeal notch to the hyoid. The lateral surfaces of the membrane contain an aperture for the internal branches of the superior laryngeal nerves, the superior laryngeal artery, and lymphatics.

The normal swallowing mechanism includes laryngeal elevation, posterior deflection of the epiglottis, inhibition of respiration, and closure of the vocal cords to prevent aspiration.[2]

The thyrohyoid membrane connects the thyroid cartilage to the hyoid bone and facilitates the superior movement of the larynx during swallowing. It is separated from the hyoid body by a bursa that facilitates this upward movement during swallowing.

The thyrohyoid membrane also provides cranial support and suspension.[3]

The lower respiratory system begins its development during the fourth week as an outgrowth of the ventral wall of the foregut, also known as the respiratory diverticulum. The endodermal lining of the respiratory diverticulum gives rise to the epithelial lining of the trachea, bronchi, alveoli, and larynx.

The cartilaginous and muscular components of the larynx, including the thyrohyoid membrane, are derived from the fourth and sixth pairs of pharyngeal arches. The superior laryngeal nerve (a branch of CN X) supplies the part of the larynx that develops from the fourth pharyngeal arch, and the recurrent laryngeal nerve (a branch of CN X) supplies the part that derives from the sixth pharyngeal arch.[4]

The superior and inferior laryngeal arteries supply most of the blood to the larynx.

The superior laryngeal artery is a branch of the superior thyroid artery near its bifurcation from the external carotid artery. It enters the larynx with the internal branch of the superior laryngeal nerve through the aperture of the thyrohyoid membrane. It supplies blood to the muscles, mucous membrane, and glands of the larynx, and will anastomose with the superior laryngeal artery from the opposite side.

The inferior laryngeal artery starts at the inferior thyroid branch of the thyrocervical trunk, a branch of the subclavian artery. It ascends into the larynx along with the recurrent laryngeal branch of the vagus nerve.[1]

The lymphatic system of the larynx can be differentiated based on if draining from above or below the vocal folds:

• Lymph drainage from above the vocal folds travels along the superior laryngeal artery, passing through the foramen in the thyrohyoid membrane, and drain into the deep cervical lymph nodes at the bifurcation of the common carotid artery.
• Lymph drainage from below the vocal folds travels along the inferior thyroid artery and drain to the upper tracheal lymph nodes.[5]

The superior laryngeal nerve and recurrent laryngeal branches of the vagus nerve mainly innervate the larynx.

The superior laryngeal nerve arises from the inferior ganglia of the vagus nerve and descends adjacent to the pharynx, behind the internal carotid artery prior to splitting into the internal and external branches.

The branch of the superior laryngeal nerve (aka the external laryngeal nerve) descends beneath the sternothyroid muscle to supply the cricothyroid muscle. This is the only muscle of the larynx that is not supplied by the recurrent laryngeal nerve.

The internal branches of the superior laryngeal nerve (aka the internal laryngeal nerve) transverse with the superior laryngeal artery through the aperture in the thyrohyoid membrane. It provides sensory innervation to the laryngeal cavity superior to the level of vocal folds. It is responsible for the sensory afferent part of the cough reflex.

The recurrent laryngeal branches of the vagus nerve supply sensation to the laryngeal cavity below the level of the vocal folds. They run immediately posterior to the thyroid gland and are responsible for innervation of all the muscles of the larynx except the cricothyroid, and for sensation inferior to the vocal folds.[6]