Malignant tumors of the pharyngeal tonsil

Anatomy and localization

The nasopharynx represents the upper compartment of the pharyngeal mucosal space. Its anatomical boundaries are strictly defined: superiorly by the skull base, posteriorly by the anterior arch of the first cervical vertebra (C1), inferiorly by the superior surface of the soft palate, and anteriorly by the choanae.

The lateral wall includes the torus tubarius (torus tubarius), the pharyngeal opening of the auditory tube, and the fossa of Rosenmüller (fossa of Rosenmüller). This posterior pharyngeal recess is the preferred site of origin for nasopharyngeal carcinoma. The tumor can develop insidiously here until it begins to destroy neighboring anatomical barriers. The most critical of these barriers is the pharyngobasilar fascia, which appears on MRI as an "inverted crown" and separates the lymphoid tissue from the parapharyngeal (laterally) and prevertebral (posteriorly) spaces.

Features of nasopharyngeal carcinoma

Among malignant processes in this zone, undifferentiated carcinoma predominates, although keratinizing and non-keratinizing forms also occur. The disease has a distinct geographic distribution, with extremely high incidence rates in Southeast Asia.

A crucial trigger for development is the Epstein-Barr virus (EBV). In clinical practice, antibody titers against this virus are used as a reliable tumor marker to assess disease activity.

The tumor is characterized by extremely aggressive behavior. By the time of detection, the vast majority (90%) of patients already have regional lymph node involvement. Hematogenous dissemination is also common, primarily to the liver and bones. Therefore, head and neck imaging must carefully evaluate bony structures, and PET is frequently included in the workup protocol.

Routes of invasion and diagnostic imaging

Tumor spread occurs via several typical routes, knowledge of which is critical for the radiologist:

• Lateral infiltration: breach of the pharyngobasilar fascia with extension into the fatty tissue of the parapharyngeal space. From there, the cancer spreads perineurally through the foramen ovale (foramen ovale) along the branches of the mandibular nerve (V3).
• Superior-posterior pathway: extension into the cranial cavity through the foramen lacerum (foramen lacerum).
• Direct destruction: erosion of the skull base bones.

For precise staging and planning of intensity-modulated radiation therapy (IMRT) or proton therapy, MRI is the method of choice. T2-weighted images allow detailed tracking of fat and muscle infiltration, for instance, by comparing the affected side with the intact prevertebral muscle.

Differential diagnosis and treatment

Any nasopharyngeal mass requires the exclusion of other pathologies. Malignant and pseudomalignant alternatives include non-Hodgkin lymphoma (NHL), minor salivary gland carcinoma, and IgG4-related disease.

Among benign conditions, adenoid hypertrophy is most common, differing on MRI by symmetry, visible mucosal folds, and a characteristic striated contrast enhancement pattern. Tornwaldt cysts and retention cysts are also encountered—they have well-defined borders and are covered by normal mucosa. When in doubt after endoscopy, biopsy is indicated.

Management of confirmed cases requires a tumor board involving oncologists, otorhinolaryngologists, pathologists, and radiologists. The primary treatment modality is radiation therapy or chemoradiation. Surgery is rarely used, mainly for local recurrences or to remove resistant lymph nodes.

What else to study on this topic

• Anatomy and imaging appearance of the pharyngobasilar fascia
• Squamous cell carcinoma of the oropharynx (SCC): localization and spread pathways
• Differential diagnosis of benign nasopharyngeal cysts (Tornwaldt cyst and retention cysts)
• Complications of tonsillar abscesses and markers of masticator space involvement

Other topics in the "Additional Topics" section

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