Anatomy

The mouth extends from the lips and cheeks to the oropharyngeal isthmus at the palatoglossal fold. It comprises a number of subsites, which can be divided into three functional types although the microscopic structure of each varies subtly from one region to the next. "Masticatory mucosa" is found on the maxillary and mandibular gingivae, the hard palate and on the dorsum of the tongue. It is bound tightly to underlying tissue and covered by keratotic, relatively thick, stratified squamous epithelium to withstand the trauma of chewing. In contrast, "lining mucosa" is elastic and is present on the inner aspect of the lips, on the buccal mucosae and their respective upper and lower sulci, the ventral surface of the tongue and the floor of the mouth. It is covered by relatively thin, stratified squamous epithelium supported by loosely textured fibrovascular connective tissue (Figures 13.1 and 13.2). "Specialised mucosa" refers to the taste buds.

The lips are composed of skin and mucosa around the opening to the mouth. They contain the orbicularis oris, fibrofatty tissue and many minor salivary glands. Upper and lower lips join at the buccal commissure (angle of the mouth). The mucosa of the lips begins at the vermilion border

Figure 13.1. Mucosal subsites of lips and oral cavity. 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.

Hard palate muscle of tongue, maxillary sinus, skin

Oral cavity: tumour invades through cortical bone, deep (extrinsic)

Lower buccal sulci

Buccal mucosa

Hard palate muscle of tongue, maxillary sinus, skin

Oral cavity: tumour invades through cortical bone, deep (extrinsic)

Lower buccal sulci

Buccal mucosa

Floor of mouth

Figure 13.2. Mucosal subsites of tongue and floor of mouth demonstrating pT4 tumour of tongue. 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.

Iwíwvll / Ventral surface of tongue

Floor of mouth

Figure 13.2. Mucosal subsites of tongue and floor of mouth demonstrating pT4 tumour of tongue. 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.

with skin and extends across the free surface into the oral cavity proper. The cheeks are continuations of the lips; the skin forms most of the facial skin while the buccal mucosa is continuous through the upper and lower sulci with the gingivae and with the soft palate/oropharynx. Buccinator is the principle muscle of the cheek; it is perforated opposite the upper second molar tooth by the parotid duct. Many minor salivary glands lie between the muscle layer and the mucosa while the facial (or buccal) lymph node lies external to buccinator below the level of the occlusal plane.

The gingival margin has a scalloped outline as it encircles the teeth, forming the interdental papilla between adjacent teeth. Behind the last molar tooth on each side of the mandible, the gingiva forms a flat triangular region known as the retromolar trigone (or retromolar pad). The hard palate is formed mostly by the palatine processes of the maxillary bones and is covered by mucosa continuous with the upper gingivae. In the midline of the palate anteriorly just behind the incisor teeth, there is a small mucosal elevation called the incisive papilla. In the anterior palate the mucosa forms four or five transverse ridges called rugae while posteriorly it is smooth. Small numbers of minor salivary glands are present in the hard palate posteriorly and laterally close to the alveolar processes of the maxilla. The hard palate is continuous posteriorly with the soft palate, a mobile flap of mucosa, striated muscle and fibrofatty tissue separating the nasopharynx from the oropharynx.

The floor of the mouth is a horseshoe-shaped region between the tongue, the mandible and mylohyoid. It contains the sublingual salivary glands, the submandibular ducts, the lingual nerves and some of the extrinsic muscles of the tongue. Right and left submandibular ducts converge on the lingual frenulum, a midline fold running from the ventral surface of the tongue to the gingiva behind the lower central incisor teeth, forming a mucosal papilla in the floor of mouth approximately 1 cm posterior to the lingual gingiva.

The tongue is divided into two parts by a V-shaped groove called the sulcus terminalis; the anterior two-thirds lies within the oral cavity and the posterior one-third (the base) lies within the oropharynx. The anterior two-thirds is divided into:

Dorsal surface - the superior surface. It is covered by enumerable filiform papillae; between 30 and 50 dispersed fungiform papillae measuring approximately 1 mm in diameter and between 8 and 12 circumvallate papillae, measuring between 3 and 4 mm in diameter located in a line just anterior to the sulcus terminalis. The fungiform and circumvallate papillae bear taste buds. Ventral surface - the inferior aspect. It has a smooth surface, merging with the floor of the mouth. Lateral border - the side of the tongue. It extends from the tip to the palatoglossal arch (anterior pillar of the fauces).

The posterior one-third of the tongue has a cobblestone surface due to the accumulation of lymphoid tissue from the lingual tonsil. No papillae are present although taste buds may be numerous. The mucosa is contiguous with the palatine tonsils laterally and the vallecula of the epiglottis posteriorly.

The tongue is divided into right and left halves by a median fibrous septum, which is attached inferiorly to the hyoid bone. The muscles of the tongue are divided into the intrinsic group and the extrinsic group. The extrinsic group represents genioglossus, hyoglossus, stylogossus and palatoglossus, having attachments outside the tongue and considered important in the staging of malignant tumours; involvement of the extrinsic muscles by tumour signifies pT4 staging (Figure 13.2).

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