Topographic anatomy of the larynx

Ligamentous Apparatus and Important Topographic Zones

The ligaments of the larynx play a crucial role not only in the biomechanics of the organ but also in the surgeon's clinical practice.

• Cricothyroid ligament (lig. cricothyroideum) is stretched between the corresponding cartilages. While its lateral parts are covered by muscles, the median cone-shaped part is completely free. This is precisely where conicotomy—the opening of the larynx via a transverse incision—is performed in acute upper airway obstruction.
• Thyrohyoid membrane (membrana thyrohyoidea) connects the thyroid cartilage (cartilago thyroidea) with the hyoid bone. Externally, it is covered by muscles. An important topographic feature: a mucous bursa lies between the body of the hyoid bone and the membrane. In pathological processes, it becomes a site of formation of phlegmons or median cysts of the neck.

Compartments of the Laryngeal Cavity

The laryngeal cavity (cavitas laryngis) on frontal and sagittal sections is distinctly divided into three levels:

1. Laryngeal vestibule (vestibulum laryngis) is the upper floor. It begins from the epiglottis (epiglottis) and ends at the level of the vestibular folds (plicae vestibulares). The slit between these folds is called the rima vestibuli.
2. Laryngeal ventricle (ventriculus laryngis) is the middle, interligamentous compartment. It is located between the vestibular folds and the true vocal folds. Superiorly, the ventricles continue into the so-called laryngeal saccules (sacculi laryngis).
3. Infraglottic cavity (cavitas infraglottica) is the lower floor. This is the subglottic space that smoothly transitions into the trachea.

Vocal apparatus: The true vocal cords (ligg. vocalia) attach to the vocal processes (processus vocalis) of the arytenoid cartilages. They project into the lumen of the larynx more strongly than the vestibular folds. The space between them forms the rima glottidis (rima glottidis).

Muscles of the larynx

The muscular apparatus is divided into two large groups:

• Extrinsic muscles move the larynx as a whole (elevating and depressing it). They attach to the hyoid bone and the sternum (mm. sternohyoideus, sternothyroideus, thyrohyoideus).
• Intrinsic muscles control the cartilages and vocal cords. The cricothyroid muscle lies on the outer surface (m. cricothyroideus). On the posterior and lateral surfaces are the posterior and lateral cricoarytenoid muscles (m. cricoarytenoideus posterior et lateralis), as well as the oblique and transverse arytenoid muscles. On the inner surface are the thyroarytenoid, thyroepiglottic, and aryepiglottic muscles.

Innervation and Blood Supply

The larynx receives blood from branches of the thyroid arteries—the superior and inferior laryngeal arteries. They form rich anastomoses with vessels of the opposite side. Venous blood collects into plexuses and drains into the internal jugular (v. jugularis interna) and brachiocephalic veins (vv. brachiocephalicae).

Innervation is provided by the sympathetic trunk and branches of the vagus nerve (n. vagus):

• Superior laryngeal nerve (n. laryngeus superior): its internal branch passes under the pharyngeal mucosa at the bottom of the piriform sinus (recessus piriformis), forming the fold of the same name.
• Recurrent laryngeal nerve (n. laryngeus recurrens): the main motor nerve of the larynx. It innervates all of its muscles except the cricothyroid. It also provides sensation to the mucosa below the glottis down to the 3rd tracheal ring.

The topography of the recurrent nerves is asymmetric: The right one branches off at the level of the right subclavian artery, looping around it from below. The left one branches off significantly lower—at the lower edge of the aortic arch, looping around it near the ligamentum arteriosum. Both nerves ascend in the groove between the trachea and esophagus, entering the larynx through the cricothyroid articulation along with the inferior laryngeal vessels. The innervation zones of the nerves overlap in the middle segment of the larynx.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topography of fascial spaces of the neck: spatium retroviscerale and previscerale
• Piriform sinuses: connection between the larynx and pharynx
• Neck fasciae according to Shevkunenko (fascia prevertebralis and endocervicalis)
• Detailed function of each intrinsic muscle of the larynx
• Variant anatomy of the relationship between the recurrent nerve and the inferior thyroid artery

Other topics in "Topographic Anatomy of the Neck"

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