c) Laryngopharynx

Structure

The laryngopharynx is the most inferior part of the pharynx. It communicates with the oropharynx above, the oesophagus below and the larynx (through the laryngeal inlet) anteriorly. The division of the oropharynx from the laryngopharynx is the tip of the epiglottis. The oesophagus begins at at the level of the inferior border of the cricoid cartilage.
The larynx bulges into the anterior wall of the laryngopharynx, giving the cavity a U-shaped structuer when viewed on a tranverse plane. The spaces on either side of the larynx are the piriform fossae, bounded medially by the aryepiglottic fold and laterally by the thyroid cartilage. The branches of the recurrent laryngeal nerve (inferior laryngeal nerve) pass beneath the mucous membrane at this point.
The hypopharynx is a clinical term for that part of the pharynx which is posterior to the larynx and corresponds fairly well with the laryngopharynx.

Relations

Anteriorly, with the larynx and laryngeal inlet. Anterolaterally with the thyroid cartilage.
Laterally, with the carotid sheath and its contents. Inferolaterally with the lateral lobe of the thyroid gland.
Posteriorly, with the vertebral column and prevertebral muscles. The retropharyngeal space lies between the pharyngeal constrictors and the prevertebral fasica.
Superiorly, with the oropharynx.
Inferiorly, with the trachea and oesophagus.

Macroscopic Appearance

The laryngopharynx is lined by a pink mucosa and has no distinguishable features on its lateral or posterior wall. Anteriorly, the mucosa is continuous with the mucosa of the superiror larynx at the aryepiglottic fold. This fold is notable for the cuneiform and corniculate cartilages which cause slight prominences on its posterior part.

Microscopic Appearance

The laryngopharynx is lined by non-keratinising, stratified squamous epithelium. It may possess small salivary like glands in the submucosa.

Physiological Variations

During swallowing, the hyoid bone elevators may pull the laryngopharynx superiorly. This has the effect of closing the laryngeal inlet by opposing the aryepiglottic folds with the epiglottis.

Neurovascular Supply

Arterial Supply

The ascending pharyngeal artery and branches of the thyroid arteries supply the muscles and mucosa of the laryngopharynx.

Venous Drainage

Veins drain to the pharyngeal venous plexus and then to the internal jugular vein.

Lymphatic Drainage

Lymph from the laryngopharynx joins a lymphatic plexus that lies in the submucosa. From here, lymph is directed to the deep cervical nodes (levels III/IV). Lymph may also pass posteriorly to retropharyngeal nodes, or inferiorly to paratracheal nodes.

Innervation

Nerves to the laryngopharynx arise from the pharyngeal plexus, and receives sensory and motor innervation from the vagus (X) nerve and superior cervical plexus. The plexus lies at the level of the middle constrictor, and branches pass inferiorly outside the constrictor muscles to their appropriate levels.

Routes of Cancer Spread

Local Invasion

Laryngopharyngeal tumours may invade into the larynx or laryngeal nerves, causing hoarseness of voice or aspiration. Lateral spread of tumours may invade the carotid sheath and cause bleeding. Posterior invasion may occur into the vertebral bodies. Extensive mass in the laryngopharynx can cause odynophagia, dysphagia or upper airway obstruction.

Lymphatic Spread

Lymphatic spread of tumours often occurs early and can be bilateral. Involved nodes are usually in the lower part of the deep cervical chain (levels III/IV) although retropharyngeal and paratracheal nodes may be involved.


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