Anatomy

The pharynx connects the nasal cavities and mouth with the larynx and oesophagus. It is divided into three functional parts, namely the nasopharynx, the oropharynx and the hypopharynx (Figure 15.1).

The nasopharynx lies behind the nasal cavities and above the level of the soft palate. The roof and posterior wall relate closely to the skull base and the first cervical vertebra. The lateral wall is an extension of fascia from the skull base called the pharyngobasilar fascia. The Eustachian tube opens into the lateral wall of the nasopharynx just behind and at approximately the same level as the inferior turbinate. It is lined by respiratory mucosa with accessory mucous glands, particularly numerous around the opening of the Eustachian tube. The slight depression posterior to the opening of the Eustachian tube is called the fossa of Rosenmuller (or pharyngeal recess). The oropharynx extends from the soft palate into the depth of the vallecula, the gutter between the posterior tongue and the epiglottis. The tonsillar fossa lies in the lateral aspect, between the palatoglossal and palatopharyngeal folds. The hypopharynx extends from the upper border of the epiglottis to the lower border of the cricoid cartilage. A narrow recess termed the piriform fossa lies on each side of the larynx between the aryepiglottic fold and the thyroid cartilage. Together with the oropharynx, it is lined by stratified squamous epithelium and contains accessory mucous glands (Figure 15.1).

A ring of lymphoid tissue surrounds the opening of the pharynx, comprising the pharyngeal tonsil (or adenoid), the palatine tonsils and the lingual tonsil. The adenoid lies on the posterior wall of the nasopharynx in the midline between the posterior edge of the nasal septum and the openings of right and left Eustachian tubes. The palatine tonsils each lie in their tonsillar fossa. This group of lymphoid aggregates is collectively described as Waldeyer's ring.

The larynx lies between the posterior one-third of the tongue superiorly and the trachea infe-riorly. It is composed of three large midline cartilages - the epiglottis, the thyroid and the cricoid - with the smaller paired arytenoid cartilages. Other smaller paired cartilages are present, the corniculate and cuneiform cartilages, that are of lesser importance in surgical practice.

The cricoid cartilage is the most inferior of the laryngeal cartilages but is the cornerstone of the larynx. It is shaped like a signet ring, with the broadest part, the lamina, located posteriorly and the narrower arch continuous anteriorly encircling the opening to the trachea. It is connected to the highest tracheal cartilage by the cricotracheal ligament. The thyroid cartilage overlaps outside the cricoid cartilage. It is composed of two quadrangular laminae that join in the midline anteriorly (forming the laryngeal prominence or "Adam's apple") and diverge posteriorly, ending as two slender processes, a larger superior cornu and a smaller inferior cornu. It is attached to the cricoid by the cricothyroid membrane and to the hyoid bone above by the thyrohyoid membrane. The epiglottis is a thin leaf-shaped cartilage, attached at its inferior aspect to the inner

Base of skull Fossa of Rosenm├╝ller

Base of skull Fossa of Rosenm├╝ller

Figure 15.1. Anatomy of the pharynx. View of pharynx opened from behind to reveal major subdivisions and anatomical landmarks of the pharynx. Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

Figure 15.1. Anatomy of the pharynx. View of pharynx opened from behind to reveal major subdivisions and anatomical landmarks of the pharynx. Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

surface of the thyroid cartilage just below where the thyroid laminae join anteriorly and extending superiorly and posteriorly to overhang the inlet to the larynx. The whole assembly is suspended from the hyoid bone by the thyrohyoid and hyoepiglottic membranes (Figure 15.2).

Right and left arytenoid cartilages are smaller than the epiglottis, thyroid and cricoid cartilages and are pyramidal in shape. They sit on top of the cricoid lamina, just lateral to the midline and are overlapped outside by the thyroid laminae. They each possess a muscular process (posteriorly and laterally), a vocal process (anteriorly) and an apex (superiorly and posteriorly). Extending anteriorly from the vocal process of each arytenoid to the inner surface of the thyroid cartilage is the vocal ligament. Each vocal ligament forms the basis of the vocal cord. A complex arrangement of extrinsic and intrinsic muscles coordinates the movements of the larynx and its constituent cartilages.

The surface anatomy of the larynx is defined by three sets of prominent mucosal folds - the aryepiglottic folds, the vestibular folds and the vocal cords. The aryepiglottic folds sweep upwards and laterally from the arytenoid cartilages posteriorly to the tip of the epiglottis, encircling the

Epiglottis

Lamina of cricoid cartilage

Superior cornu of thyroid cartilage

Position of arytenoid cartilage (on interior)

Epiglottis

Lamina of cricoid cartilage

Superior cornu of thyroid cartilage

Position of arytenoid cartilage (on interior)

Arytenoid Cartilages Position

Cricothyroid membrane

Lamina of cricoid cartilage a b

Figure 15.2. The laryngeal cartilages. (a) View from the right lateral aspect. (b) View from the posterior aspect.

Hyoid bone

V^ Thyrohyoid membrane

Tracheal rings

Cricothyroid membrane

Lamina of cricoid cartilage a b

Figure 15.2. The laryngeal cartilages. (a) View from the right lateral aspect. (b) View from the posterior aspect.

inlet to the larynx and representing the border between larynx and hypopharynx. The vestibular folds (or false cords) lie just above the vocal cords and run in the horizontal plane parallel to the vocal cords, separated from them by a shallow pouch called the vestibule (or ventricle). The larynx is divided into three regions - supraglottic, glottic and subglottic - according to their relationship with the vocal folds. The glottic region corresponds to the region of the vocal cords, while supraglottic and subglottic regions lie above and below respectively (Figure 15.3). A number of compartments are present within the larynx that can influence the spread of tumours. The pre-epiglottic space lies outside the larynx between the tongue, the hyoid bone and the epiglottis while the supraglottic space lies just below the mucosa of the supraglottic larynx from epiglottis to the false cords, these spaces communicating through fenestrations in the epiglottis. The paraglottic space lies between the vocal ligament and the lamina of the thyroid cartilage and communicates superiorly with the pre-epiglottic and supraglottic spaces. Reinke's space is restricted to the submucosa of the vocal cord, communicating with the paraglottic space and the subglottic space, the latter extending submucosally from the vocal cord into the trachea.

The larynx is covered almost entirely by respiratory mucosa with many seromucinous accessory glands in the submucosal tissues, particularly around the epiglottis and the vestibule. In contrast, the vocal cords are covered instead by stratified squamous epithelium with only a minimum of connective tissue around the vocal ligaments in which few (if any) lymphatic channels are found.

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