Parotid gland tumors include a variety of benign and malignant entities that are also found in other salivary glands (see salivary gland tumors). The frequency of different tumors varies considerably among the salivary glands with the parotid gland hosting the majority of all salivary gland tumors, the majority of which are benign.
Given its anatomical relationship including the facial nerve that runs through the gland and the unique presence of intraglandular lymph nodes, clinical presentation and nodal tumors are distinct from many other salivary gland tumors.
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Epidemiology
The demographic of affected individuals will vary according to the tumor type. Generally, parotid gland tumors are encountered in middle age group. They are rare in the pediatric populations with pleomorphic adenomas and mucoepidermoid carcinoma being the most common 4. One entity notable from a demographic point of view: lymphomatous papillary cystadenomas (Warthin tumors) are almost only ever seen in the parotid gland and are strongly associated with elderly male individuals 1,4.
Clinical presentation
Parotid gland tumors most commonly present as lumps in the preauricular region, over or behind the angle of the mandible. Perineural spread may result in ticks in the muscles of facial expression, neurogenic pain or weakness 1. Local invasion into nearby muscles of mastication (masseter, pterygoids) can result in trismus and pain 1,2. Extra-glandular nodal spread can present with lymph node enlargement superficial to the parotid gland and infra auricular nodes and upper internal jugular (deep cervical) nodes (level II) 3.
Pathology
The WHO classification of head and neck tumors recognizes many salivary gland tumors. Most can occur in the parotid gland, but some are far more common than others 1,4.
Although approximately 70% of all parotid tumors are benign, given the overall higher frequency of tumors of the parotid gland compared to other salivary glands, 70% of all malignant salivary gland cancers arise in the parotid 1,4.
Primary salivary tissue tumors
Benign
pleomorphic adenoma: most common; 50% of all parotid gland tumors
lymphomatous papillary cystadenomas (Warthin tumor): second most common, almost exclusively found in the parotid
Malignant
mucoepidermoid carcinoma: most common; 30% of all malignant partotid gland tumors 1
adenoid cystic carcinoma: 20-25%
acinic cell carcinoma: 10-15%
Secondary tumors
Benign
lipoma
schwannoma
Malignant
-
metastatic disease from face, ear, scalp nasopharyn and soft palate 3
squamous cell carcinoma (most common)
other primaries
Radiographic features
From a diagnostic and staging point of view, CT and MRI are the primary modalities, having complementary strengths. CT is readily available and excellent at imaging bony involvement. MRI is better at perineural spread.
Ultraound is less relevant for diagnosis but enables biopsy (both FNAC and core biopsy).
Although PET lacks specificity, it is useful in assessing for distant nodal spread 1.
The specific features of each tumor are discussed separately.