List and discuss the benign tumors of the major salivary glands.

Benign Major Salivary Gland Tumors

Overview and Classification

Pleomorphic adenoma is the most common benign salivary gland neoplasm, occurring predominantly in the parotid gland in middle-aged women, followed by Warthin tumor as the second most frequent benign tumor. 1, 2

The major benign epithelial salivary gland tumors include:

• Pleomorphic adenoma (most common) 1, 2
• Warthin tumor (papillary cystadenoma lymphomatosum) 1, 3
• Basal cell adenoma (four subtypes: solid, trabecular, tubular, and membranous) 1
• Oncocytoma 1
• Myoepithelioma 1
• Canalicular adenoma 1
• Cystadenoma 1
• Papillomas (intraductal and inverted) 1
• Lymphadenoma 1
• Sebaceous adenoma 1
• Sialadenoma papilliferum 1

Clinical Significance and Malignant Transformation Risk

High-Risk Tumors

Pleomorphic adenoma carries a considerable 5-15% risk for malignant transformation into carcinoma ex pleomorphic adenoma, making accurate diagnosis and complete excision critical. 1

• Basal cell adenomas can occasionally develop into malignancy, though to a much lesser degree than pleomorphic adenoma 1
• Warthin tumors rarely undergo malignant transformation 1

Low-Risk Tumors

The remaining eight benign tumor types (oncocytoma, myoepithelioma, canalicular adenoma, cystadenoma, papillomas, lymphadenoma, sebaceous adenoma, sialadenoma papilliferum) virtually never develop into malignancy 1

Recurrence Patterns

High Recurrence Risk

Pleomorphic adenoma has a rather high risk for recurrence, with the most important causes being enucleation with intraoperative spillage and incomplete tumor excision due to its incomplete pseudocapsule and presence of pseudopodia. 4, 1

• Most recurrent pleomorphic adenomas are multinodular and multifocal 4
• A high percentage of recurrent pleomorphic adenomas are incurable despite multiple treatment procedures 4

Occasional Recurrence

The following tumors only occasionally recur: 1

• Sialadenoma papilliferum
• Oncocytoma
• Canalicular adenoma
• Myoepithelioma
• Membranous type of basal cell adenoma
• Warthin tumor (though reappearance often represents metachronous occurrence of new foci rather than true recurrence) 4

Virtually No Recurrence

These tumors virtually never recur: 1

• Intraductal and inverted papillomas
• Lymphadenoma
• Sebaceous adenoma
• Cystadenoma
• Basal cell adenoma (solid, trabecular, and tubular subtypes)

Diagnostic Approach

Providers should perform imaging (neck ultrasound, CT with IV contrast, and/or MRI of the neck and primary site) in patients with a suspicion of a salivary gland mass to localize the lesion and detect additional masses or nodal metastases. 5

• Ultrasound is often first-line in children due to lack of ionizing radiation and no requirement for patient immobility 5
• Cross-sectional imaging with CT or MRI offers superior localization and detection of additional masses, though imaging has diagnostic limitations in distinguishing benign from malignant tumors 5
• CT and ultrasound may assist in guidance for FNA or biopsy, providing greater accuracy for pathologic diagnosis 5

Treatment Strategies

Pleomorphic Adenoma

The optimal treatment is superficial or total parotidectomy with facial nerve preservation, which results in local control rates of 95% or higher. 2

• Complete excision outside the tumor capsule is mandatory to prevent recurrence 5
• For major gland tumors, complete excision of the gland is standard 5
• For minor gland tumors, wide radical resection must be undertaken 5

Recurrent Pleomorphic Adenoma

Total parotidectomy is generally recommended for recurrent pleomorphic adenoma given the multicentricity of the lesions, though surgery alone may be inadequate for long-term control. 4

• MRI is the imaging method of choice for assessment of recurrent disease 4
• There is growing evidence that postoperative radiotherapy results in significantly better local control 4
• Radiotherapy achieves local control rates of approximately 80-85% for microscopic residual tumor and 40-60% for gross residual tumor 2
• Nerve integrity monitoring may reduce morbidity during surgery for recurrent disease 4

Warthin Tumor

Conservative surgical management including partial superficial parotidectomy or extracapsular dissection is appropriate, with selected cases eligible for observation. 4

• Reappearance often represents metachronous occurrence of new foci or residual incomplete excision of multicentric primary foci rather than true recurrence 4

Other Benign Tumors

Conservative surgical excision is appropriate for other benign salivary gland neoplasms including myoepithelioma, basal cell adenoma, oncocytoma, canalicular adenoma, cystadenoma, and ductal papilloma, as they follow an indolent course with rare recurrence. 4

Critical Pitfalls

• Never perform enucleation of pleomorphic adenoma, as this leads to high recurrence rates due to intraoperative spillage and incomplete excision of pseudopodia 4
• Patients with recurrent pleomorphic adenoma must be informed about the possibility of needing multiple treatment procedures, potential facial nerve impairment, and possible need for radiation therapy 4
• No biomarker has been found relevant for predicting recurrence or potential malignant development, making complete surgical excision the cornerstone of management 1
• The main surgical complication is 7th nerve injury, which must be balanced against the need for complete tumor excision 2