Oropharynx cancer

Tongue base cancer tends to grow silently and deeply, and is often larger than suspected at clinical examination; it does not extend into neighbouring structures unless situated in the periphery of the tongue base. Peripheral tumours may spread to the anterior tonsillar pillar, but this is less frequently seen than spread of tonsillar cancer to the tongue base. Anterior spread into the floor of the mouth may occur (Fig.1). Spread to the valleculae and pyriform sinuses, and into the pre epiglottic space may be seen.

Nearly all tonsillar cancers originate from the anterior tonsillar pillar. These cancers show spread anteroinferiorly to the tongue base, and superomedially spread to the soft palate, both along the palatoglossal muscle (Fig.2). Anterolateral spread to the retromolar trigone is also commonly seen. Advanced lesions may invade the mandible, and spread along the pharyngeal wall to the nasopharynx or through the pharyngeal wall into the parapharyngeal space (Fig.3).

Soft palate cancer may spread laterally along the tonsillar pillars.

The upper parajugular lymph nodes are the first at risk for lymphatic spread from an oropharyngeal cancer. Lymphadenopathy head and neck at other sites may be present, especially in advanced disease.

Diagnostic imaging

Imaging is performed to evaluate the tumour extent as described above. Both CT and MRI are adequate modalities; CT has the advantage of simultaneously allowing complete evaluation of the neck lymph nodes. In normal circumstances, the deep tissue planes at the level of the oropharynx should appear symmetrical. Infiltration of these deep tissues is a reliable sign of invasive disease. The apperance of superficial tissue planes is more variable, mainly because of the lymphoid tissue present in the oropharyngeal walls. Superficial tissue asymmetry, without infiltration of the deeper tissues, can be a normal variant or caused by early cancer.

RH