Pathology of the Head and Neck

198 N. Gale · A. Cardesa · N. Zidar77.1 Summary of Anatomy,Histology and EmbryologyThe larynx and hypopharynx are constituent parts ofthe upper aerodigestive tract, intimately linked togetherwith their connective tissue elements and differentepithelia. The anatomy and histology of both organsare very complex and details are available in variousstandard textbooks and specialised papers [103, 158,238, 321, 322]. Only essential data will be given here.The larynx is a hollow tube that communicatescranially with the hypopharynx. Its upper limits arethe free edge of the epiglottis and the two aryepiglotticfolds. The lower laryngeal part continues caudallywith the trachea, and its inferior limit is the loweredge of the cricoid cartilage. The anterior border consistsof the lingual surface of the epiglottis, thyrohyoidmembrane, thyroid cartilage and the anterior arch ofthe cricoid cartilage. Posteriorly, the cricoid cartilageand area of the arytenoids limit the larynx.The larynx is divided into supraglottic, glottic andsubglottic regions, which have particular significancefor the biological behaviour and staging of tumours.The supraglottic region extends from the tip of the epiglottisdown to the superior edge of the true vocal cordand includes the epiglottis, aryepiglottic folds, arytenoids,the false vocal cords and ventricles. The glottisincludes the vocal cords with anterior and posteriorcommissures. The subglottis extends below thetrue vocal cords to the lower border of the cricoid cartilage.Our own experience suggests that marked variationsin the distribution of different types of laryngeal epitheliarelated to age seem to be the rule [177]. The lingualand, variably, laryngeal side of the epiglottis andthe true vocal cords are covered by the non-keratinisingstratified squamous cell epithelium, the rest of thelarynx is lined with the respiratory epithelium. The seromucinousglands are abundant in all compartmentsof the larynx except in the vocal cords, where they areessentially missing on their free edges and are sparse inthe rest of the cords.It is important to draw attention to some particularitiesin the laryngeal structure that considerably influencethe spread of malignant tumours. The elasticcartilage of the epiglottis with numerous fenestrationsfor vessels, nerves and glands provides a “locus minorisresistentiae” for the progress of malignant growthfrom the laryngeal to the lingual side or vice versa. Inthe anterior commissure, where the true vocal cordsmeet in the anterior midline, a band of fibrous tissue(protrusions of the two vocal ligaments) with lymphaticand blood vessels is attached to the thyroid cartilage.There is no perichondrium at this point, whichcertainly facilitates the ingrowth of malignant tu-mours in the thyroid cartilage. The network of capillariesis poorly developed in Reinke’s space of the vocalcords and lymphatics are lacking. These specificitiescontribute to the development of various exudativelesions of the vocal cords and delayed metastasesof glottic cancers.Embryologically, the supraglottic part of the larynxarises from the third and the fourth branchial arches,while the glottic and subglottic portions are derivedfrom the sixth arch. The first appearance of the respiratorytract occurs at approximately 21 days duringembryogenesis as an evagination or a vertical grooveof the cephalic portion of the foregut. This evaginationis the precursor of the epiglottis, the earliest portion ofthe larynx. Its outlines appear at the 6-mm foetal stageby 30 days. The respiratory groove begins to close andwith the formation of the arytenoids, the closure becomescomplete [103]. The covering epithelium of thegroove appears in the 3–5-mm embryo as three lines ofpolyhedral embryonic cells of endodermal origin. In a30-mm foetus, by 60–70 days, the thickness of the embryonicstratified squamous epithelium increases, andthe vocal cords begin to differentiate. The ciliated epitheliumoccurs in a 40-mm foetus on the epiglottis andlaryngeal vestibule. A sharp distinction between thetwo epithelia appears after the foetus reaches a lengthof 95 mm. The larynx of a newborn is covered in theciliated epithelium, except on the true vocal cords. Inaddition to this location, the stratified squamous epitheliumis also present on the interarytenoid area andon the tip of the epiglottis [158].The hypopharynx is the caudal part of the pharynxwith the wide part superiorly, extending from the tipof the epiglottis to the inferior level of the cricoid cartilage,where it becomes narrow and continuously proceedsto the oesophagus. The hypopharynx is dividedinto three compartments: left and right pyriform sinuses,postcricoidal region, and posterior pharyngealwalls. The pyriform sinuses are medially limited bythe aryepiglottic folds and laterally by the thyroid cartilage.The postcricoid area is the posterior side of thecricoid cartilage. The posterior wall is situated in frontof the cervical spine. The entire hypopharynx is coveredin the stratified squamous cell epithelium.Embryologically, the pharyngeal gut or pharynx extendsfrom the buccopharyngeal membrane to the tracheobronchialdiverticulum. The hypopharynx is almostentirely of endodermal origin. In the 8th throughto the 10th gestation week the pharynx, as well as thehypopharynx, is rather small and after the 10th weekof gestation, remarkable growth occurs in this region[204, 252].