13 Oropharynx

13 Oropharynx JJ Mazeron, E Van Limbergen

1 Introduction The oropharynx is essential in co-ordinating the complex acts of deglutition, phonation, and airway protection. Preservation of this function presents a difficult therapeutic challenge in the treatment of squamous cell carcinoma of this anatomical region. The available treatment modalities include surgery, external beam irradiation or chemoradiation, interstitial irradiation, and various combinations of the three. The wide range of results in the literature leaves considerable uncertainty as to the treatment of choice. Excision of structures important in swallowing leaves a functional impairment proportional to the extent of surgery. Simple excision of a limited tumour with adequate margins, with primary closure, is rarely possible, and is not generally considered sufficient treatment. More extensive resections often include a sub-total or a total laryngectomy and, despite reconstruction, leave considerable functional deficit. Furthermore, concern about adequate margins or lymph node involvement often results in the addition of postoperative irradiation, which further increases sequels. Considerable experience with the treatment of oropharyngeal tumours by irradiation has demonstrated the need for an elevated tumour dose to achieve local control. Unfortunately, with external beam irradiation alone, it is difficult to spare adjacent normal tissues, resulting in undesirable late effects on the salivary glands, mandible, and muscles of mastication. Interstitial implantation is ideally suited to deliver a boost dose limited to the volume of the primary tumour, thus minimising sequels. However, because of the complex anatomy and the rare incidence of the disease and its indications for using brachytherapy, these techniques should be reserved for centres with enough recruitment and experience. Anatomical Topography The oropharynx is a somewhat cubic cavity, which communicates anteriorly with the oral cavity, above with the nasopharynx, and below with the hypopharynx and the larynx. Its walls are anteriorly formed by the base of tongue, laterally by the two tonsillar regions, above by the soft palate, and posteriorly by the posterior pharyngeal wall. The base of tongue is limited anteriorly by a transverse plane passing through the lingual insertions of the palato-glossal folds, laterally by the glosso-tonsillar sulci, and posteriorly by the glosso- epiglottic sulcus or vallecula. The faucial arch is composed of the two tonsillar regions and the soft palate. The tonsil lies in a fossa formed by the anterior and posterior tonsillar pillars. This is separated from the tongue by the glossotonsillar sulcus. The two pillars merge and superiorly form the soft palate, which is anteriorly adherent to the hard palate and inferiorly supports the uvula. The tonsillar region continues anteriorly with the mucosa covering the ascending branch of the mandible, and posteriorly with the lateral wall of the oropharynx. Mucosa of the posterior pharyngeal wall is adherent to the cervical vertebrae and is usually poorly accessible to implantation. 2

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