A Guide to Clinical Differential Diagnosis of Oral Mucosal Lesions
Benign Salivary Gland Neoplasms of Oral Mucosa

Course Author(s): Michael W. Finkelstein, DDS, MS;Emily Lanzel, DDS, MS;John W. Hellstein, DDS, MS

Benign Salivary Gland Neoplasms of Oral Mucosa

Benign tumors of salivary gland origin are typically encapsulated, slowly growing, and non-tender. The overlying mucosa is normal in appearance unless it has been traumatized. Salivary gland tumors can originate throughout the oral mucosal except for the following locations: midline and anterior hard palate, gingiva, and attached alveolar mucosa. It is important to remember that some malignant salivary gland neoplasms can sometimes be slowly growing, well circumscribed and non-tender, and thus simulate a benign tumor. Tumors that can mimic a benign neoplasm include adenoid cystic carcinoma, polymorphous low-grade adenocarcinoma, low-grade mucoepidermoid carcinoma and acinic cell adenocarcinoma.

Pleomorphic adenoma*, also known as mixed tumor, is the most common tumor of salivary gland origin. The parotid gland is the most common location. The posterior lateral quadrant of the hard palate is the most common location for tumors of minor salivary glands, but it may be found in any mucosal region that contains salivary glands. Pleomorphic adenoma has clinical features similar to many other benign tumors arising from salivary glands and mesenchymal tissue. Complete surgical removal and microscopic diagnosis is the treatment. Very rarely carcinoma arises in a pre-existing pleomorphic adenoma.

Image: Pleomorphic adenoma
Pleomorphic adenoma

Monomorphic adenoma is a generic term that refers to a group of benign salivary gland neoplasms with microscopic features different from pleomorphic adenoma. This term is seldom used currently. Instead, the specific name of the adenoma is used, such as canalicular adenoma, basal cell adenoma, oncocytoma and others. Treatment is excisional biopsy and microscopic diagnosis. Complete excision of the lesion results in cure.

Papillary cystadenoma lymphomatosum, also known as Warthin tumor, probably arises from salivary gland tissue trapped within lymph nodes. Almost all cases arise in the parotid gland, and it is more common in older adults. It has been reported to occur bilaterally in 5 to 14% of cases. Surgical removal and microscopic diagnosis is the treatment for papillary cystadenoma lymphomatosum. Some authorities believe that the lesion is often multicentric, accounting for an approximately 10% recurrence (or persistence) rate. The prognosis is good.

Polymorphous low-grade adenocarcinoma* is a malignant neoplasm of salivary gland origin. It is included in the category of benign salivary neoplasms because it is usually slowly growing, of long duration, and not painful. This tumor occurs almost exclusively in minor salivary glands. Treatment is wide surgical excision. Metastasis to cervical lymph nodes is not common, and distant metastasis is rare. If the lesion recurs it can often be successfully treated by another surgical excision. The prognosis is relatively good, and few cases are fatal.

Image: Polymorphous low-grade adenocarcinoma
Polymorphous low-grade adenocarcinoma

Acinic cell adenocarcinoma is a malignant salivary gland neoplasm that is most common in the parotid gland. It typically presents as a slowly growing well circumscribed lesion that can be confused with a benign tumor. Occasionally it can be accompanied by pain or paresthesia. Complete surgical excision and microscopic diagnosis is the recommended treatment. Lesions in the major glands may require removal of the entire gland.

Adenoid cystic carcinoma* is an adenocarcinoma of salivary gland origin. It may mimic a benign tumor, but it may also present with pain. The tumor has a tendency to invade nerves. Treatment is complete surgical excision. Adenoid cystic carcinoma is characterized by recurrence and metastasis and has a very poor 20-year survival rate.

Mucoepidermoid carcinoma* is a carcinoma of salivary gland origin that contains mucous cells and squamous cells. Mucoepidermoid carcinoma has a range of microscopic features that generally correlate with the clinical behavior. Lesions that are composed predominantly of mucous cells (low-grade lesions) are slowly-growing, compressible, and relatively less aggressive. Lesions composed predominantly of squamous cells (high-grade lesions) tend to be more rapidly growing, firm, and infiltrative. It should be emphasized that all mucoepidermoid carcinomas are malignant neoplasms and have the potential to recur and metastasize. Treatment is complete surgical excision and microscopic diagnosis. The prognosis depends upon the stage (extent of spread of the tumor) and microscopic grade. Low-grade tumors have a relatively good prognosis, but high-grade tumors have a prognosis similar to squamous cell carcinoma.

Image: Mucoepidermoid carcinoma
Mucoepidermoid carcinoma
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