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Most of the tumors in the oropharynx, particularly the base of the tongue, are malignant. The majority are squamous cell carcinoma. The second most common malignant tumors are cancers of salivary gland origin, and rarely, cancers of other histologic subtypes will present in the base of tongue. Table 9.1
lists the lesions from my experience and those reported in the literature. A number of operative approaches and techniques can be employed in removing these tumors. The precise location of the tumor, the experience and expertise of the surgeon, and a host of other factors may impact the choice of the surgical approach. Note that a number of instances in which the technique of transcervical pharyngotomy has been employed in the past may have been supplanted by the use of transoral robotic surgery (TORS). Typically, transoral direct laryngoscopy is performed to allow a complete inspection of the tumor and to render a definitive histologic diagnosis in order to allow for subsequent treatment planning.
The use of this technique must be placed in the context of additional treatment options. For many patients with squamous carcinoma of the oropharynx, there are both primary surgical and nonsurgical treatment options available. Surgical options include the increased use of TORS, or laser excision, as well as mandibulotomy/mandibulectomy approaches for more advanced cancers. Chemoradiation is clearly an option for patients with both early- and advanced-stage cancer. To date, there are no definitive data showing improved survival or quality of life for either modality.
The physical examination of the patient presenting with a tumor of the oropharynx/base of the tongue requires a complete examination of the head and neck. Evaluation of the oral cavity focuses on the presence of trismus as it may impact upon surgical access. An estimation of the mobility of the tongue is essential to exclude
significant infiltration of the tongue resulting in denervation or atrophy of the hemioral tongue. A combination of transoral mirror and flexible laryngoscopic evaluation of the base of the tongue is essential. This allows for assessment of the extent of the cancer in terms of central, unilateral, or a bilateral involvement of the base of the tongue. Evaluating extension to the adjacent tonsil, lateral pharyngeal wall, posterior pharyngeal wall, supraglottic larynx, or piriform sinus is critical in planning the treatment. In many instances, the tumor extension may be subtle and imaging is complementary. Evaluation of the airway is also critical in terms of anticipating management of the airway in the operating room. Many of these patients may present only with a metastatic lymph node in the neck. Complete assessment of the at-risk cervical lymph nodes is essential for both the purpose of treatment planning and surgical access.
TABLE 9.1 Malignancies Arising from the Base of the Tongue
I. Squamous cell carcinoma
A. HPV positive
B. HPV negative
II. Minor salivary gland origin
A. Acinic cell carcinoma
C. Adenoid cystic carcinoma
D. Carcinoma—Ex pleomorphic adenoma
E. Mucoepidermoid carcinoma
A. Alveolar soft part sarcoma
E. Additional subtypes
IV. Mucosal melanoma
There are a number of surgical approaches to oropharyngeal neoplasms, specifically those arising in the base of the tongue. This includes mandibulectomy, mandibulotomy, the aforementioned transcervical pharyngotomy approach, and lastly TORS. To use a TORS approach, there must be adequate access, and trismus would be considered a significant contraindication. For the rare patients with invasion of the mandible, segmental resection of the mandible is necessary and a transcervical pharyngotomy would not be appropriate. Mandibulotomy provides outstanding access but is associated with the cosmetic deformity of a lip-split incision and the potential for a nonhealing osteotomy site.
For the patients being considered for a transcervical pharyngotomy, previous neck dissection is a relative contraindication. The ability to manage the carotid artery and potential preservation of the ipsilateral hypoglossal nerve may be hindered by a previous neck dissection or anatomy distorted by extensive scarring.
Extended procedures that require resection of the inferior aspect of the lateral or posterior pharyngeal wall can all be performed when appropriate planning has been considered. Even extended procedures such as laryngectomy can be performed via a transpharyngeal approach.
Imaging plays a critical role in the evaluation of the patient with a mass in the oropharynx. Both computed tomography (CT) and magnetic resonance imaging (MRI) are used in the evaluation of oropharyngeal neoplasms. A CT scan with contrast provides considerable insight into the extent of the primary lesion, as well as the presence of metastasis to the cervical lymph nodes. For more advanced cancers, one can determine the
extent of invasion into the intrinsic musculature of the tongue. In extensive lesions, encroachment onto or invasion of the mandible may also be evident. MRI provides slightly improved determination of the soft tissue interface between the tumor and the adjacent surrounding structures. In advanced cancer extending into the neck, it may provide valuable information in determining the relationship between the cancer and the blood vessels in the neck, specifically the internal carotid artery. MRI is equally adept at identifying lymph node metastasis.
Recently, the positron emission tomography-computed tomography (PET-CT) scan has been useful in defining the location of the cancer. This modality may provide a slightly decreased definition of the extent of the primary cancer, but it is highly adept at identifying metastasis to the cervical lymph nodes. In patients with advanced metastasis to the neck, it is often successful in identifying the small proportion of the patients with distant metastasis, most commonly to the lung and mediastinum.