17.1 Epidemiology

The floor of the mouth (FOM) represents the second most common site of malignancies in the oral cavity after the oral tongue and the most common histology is squamous cell carcinoma (SCC). FOM SCC tends to affect older (~60 years old), Caucasian males ^{2 , 4} ; however, it is not uncommon in younger persons. Traditional risk factors including smoking, chewing tobacco, spitting tobacco, and regular alcohol intake combine synergistically to increase the risk of FOM cancers. In an analysis of the Surveillance, Epidemiology, and End Results (SEER) database of 14,010 patients with FOM SCC, patients most commonly presented with early stage I or II disease (59.5%). The survival rate for patients with stages I, II, III, and IV are 90, 80, 65, and 30%, respectively.

17.2 Clinical Presentation

Patients with an FOM SCC commonly present with a mass or a painful ulcer with an irregular border (▶ Fig. 17.1, ▶ Fig. 17.2). There may be surrounding coexistent leukoplakia or erythroplakia. These lesions will continue to enlarge if neglected by patients, giving rise to more advanced symptoms including ankyloglossia with involvement of the tongue musculature, hypoglossal nerve, or mucoperiosteum of the mandible, paresthesias of the FOM and tongue with involvement of the lingual nerve, sialadenitis with involvement of the duct openings or sublingual gland, halitosis from a necrotic tumor, and referred pain to the ear. In addition, patients may initially present with a neck mass from regional lymph node metastases or even direct extension of tumors into the submental or submandibular region.

17.3 Diagnosis and Evaluation

Screening through a variety of methods including cytological brush, oral saliva, oral rinse evaluations of proteomics, gene microarray, methylation, and other assays have been described; however, there have been no robust clinical trials to validate that these tests are superior to a thorough clinical examination. For a definitive diagnosis, a tissue biopsy is still needed. This can be readily achieved under local anesthetic, followed by a punch biopsy of the edge of the tumor and normal tissue.

A thorough history and examination should be performed in all these patients, beginning with an inquiry about the presenting symptoms including pain, paresthesia, ear pain, dysphagia, odynophagia, voice change, dysarthria, trismus, bleeding, weight loss, lower lip/chin numbness, loose dentition, and preexisting dentures. This should be followed by specific questions about their past medical history and surgical history, allergies, social network and support, tobacco use, and alcohol consumption. These factors all influence the preoperative counseling and optimization of patients. It is our practice to routinely refer patients with = 10% weight loss to a dietitian for optimization of nutrition prior to surgery. The choice of surgical reconstruction, particularly if a segmental mandibulectomy is required, is dependent on the patient’s comorbidities, their willingness to undergo the surgery, and their social background and support. These factors also significantly influence the postoperative management of the patient in terms of rehabilitation and progression through to adjuvant therapies including radiotherapy and chemotherapy.

The physical examination should include a complete head and neck examination. A thorough examination, in particular, with bimanual palpation of the lesion should be attempted to ascertain the size. Laterally, fixation of the tumor through involvement of the periosteum may indicate underlying involvement of the mandible. The medial extent of the tumor edge should also be evaluated, focusing on the extent of involvement of the oral tongue. Loose dentition, particularly, adjacent to the tumor should be noted for potential invasion of the mandible. Trismus should also be noted as this will influence the choice of surgical access, which will be discussed later. The neck should then be systematically examined for the clinical determination of regional spread. This is then followed by an examination of the ear and nose. Flexible laryngoscopy should be routinely performed to evaluate for potential posterior extension of the tumor, synchronous primaries, and the status of the airway. Following this if reconstruction with a pedicled or free flap is being considered, the appropriate donor sites should be assessed, as discussed in Chapter 18.

Further evaluation involves imaging with computed tomography (CT) and magnetic resonance imaging (MRI), the two most common modalities utilized. CT is commonly used to delineate cortical bony involvement and lymph node metastases, whereas MRI is utilized to evaluate for soft-tissue invasion, perineural spread, and extension into medullary bone. CT has been shown to have a sensitivity ranging from 63 to 86% and a specificity ranging from 68 to 100% for detecting cortical bone invasion. ^{5 – 7} Cone beam CT may offer an alternative with a smaller machine, less expensive cost, an upright patient position, and a lower radiation dose, and this may have a better sensitivity (range 91-94%) at the expense of specificity (range 59-97%) for the evaluation of cortical bone invasion. ^{5 – 7} The use of PET-CT in the staging of patients is not uniform but may find a particular role in patients with advanced disease, to evaluate for distant metastases as these patients would not be candidates for curative surgical treatment and alternative options should be considered.

17.4 Relevant Anatomy

The FOM is a horseshoe-shaped area inferior to the ventral surface of tongue that is covered by a thin mucous membrane made up of nonkeratinized stratified squamous epithelium. It is bounded anteriorly and laterally by the lingual surface of the mandible and its overlying mucoperiosteum, medially by the lateral surface of the tongue. The posterior extent of the FOM extends laterally to the base of the anterior tonsillar pillar. The FOM is connected to the ventral surface of the tongue by a midline mucosal fold called the frenulum. On each side of the frenulum (from superior to inferior) are the deep lingual vein, the sublingual ridge, and the sublingual caruncles. Medially at the sublingual caruncles, the submandibular duct openings (Wharton’s duct) can be identified.

Inferiorly, the FOM is bounded by the muscular diaphragm consisting of the mylohyoid, geniohyoid, and the genioglossus muscles. Medial to the mylohyoid muscle are the sublingual gland, submandibular duct, hypoglossal nerve, and lingual nerve. The submandibular gland lies at the posterior free edge of the mylohyoid with the deep lobe situating deep to the mylohyoid muscle.

The FOM is innervated by the lingual nerve (CN V3). Lymphatic drainage of the anterior FOM is via the submental nodes that then drain bilaterally to the submandibular nodes and deep cervical nodes (Level I-III). Lymphatic drainage of the posterior FOM is toward ipsilateral submandibular nodes and then deep cervical nodes.