Residency · Residency · Otolaryngology
Salivary Gland Neoplasms: Workup and Classification
Introduction
Salivary gland neoplasms represent a diverse group of tumors with a wide spectrum of biological behavior. They account for approximately 3-6% of all head and neck neoplasms. The fundamental rule in salivary gland oncology is that the smaller the gland, the higher the probability of malignancy. A thorough understanding of classification, workup, and histopathology is critical for appropriate management.
Anatomy Review
Parotid gland: largest salivary gland; Stensen duct opens opposite the second upper molar. Submandibular gland: Wharton duct opens at the sublingual caruncle. Sublingual gland: drains via multiple ducts of Rivinus into the floor of mouth. Minor salivary glands: 600-1000 distributed throughout the oral cavity, pharynx, larynx, and sinonasal tract; palate is the most common site of minor salivary gland tumors.
Epidemiology
| Gland | % of All Salivary Neoplasms | % Malignant |
|---|---|---|
| Parotid | 80% | 20% |
| Submandibular | 10-15% | ~50% |
| Sublingual | <1% | ~80% |
| Minor salivary glands | 10-15% | 50-80% |
80% of salivary neoplasms occur in the parotid gland. Of parotid tumors, 80% are benign. Of submandibular tumors, approximately 50% are malignant. Of minor salivary gland tumors, approximately 50-80% are malignant. The "80-80 rule": 80% of salivary tumors arise in the parotid, and 80% of those are benign.
Classification of Salivary Gland Neoplasms
Benign Tumors
Pleomorphic adenoma (benign mixed tumor): most common salivary neoplasm overall (60-70%); composed of epithelial and mesenchymal elements; risk of malignant transformation (carcinoma ex pleomorphic adenoma) with prolonged observation. Warthin tumor (papillary cystadenoma lymphomatosum): second most common benign parotid tumor; bilateral in 10-15%; more common in smokers and males. Oncocytoma: rare, composed of mitochondria-rich oncocytes. Basal cell adenoma and canalicular adenoma.
Malignant Tumors
Mucoepidermoid carcinoma: most common malignant salivary neoplasm; low, intermediate, and high grade; low grade has excellent prognosis. Adenoid cystic carcinoma: characterized by perineural invasion; three patterns — cribriform (best prognosis), tubular, and solid (worst prognosis); late distant metastases (lung) even decades after treatment. Acinic cell carcinoma: low-grade malignancy; most common in the parotid. Salivary duct carcinoma: high-grade, aggressive; resembles ductal breast carcinoma; often androgen receptor positive. Carcinoma ex pleomorphic adenoma: arises within a longstanding pleomorphic adenoma; prognosis depends on extent of invasion beyond the capsule. Adenocarcinoma NOS and polymorphous adenocarcinoma.
Clinical Presentation
Painless mass in the parotid, submandibular, or oral cavity region. Pain: suggests malignancy or infection but is not specific. Facial nerve weakness: highly suspicious for malignant parotid tumor. Rapid growth: concerning for high-grade malignancy or lymphoma. Fixation to skin or underlying structures: suggests malignancy. Cervical lymphadenopathy: present in 15-25% of malignant cases.
Diagnostic Workup
Imaging
Ultrasound: first-line; differentiates solid from cystic lesions; guides FNA. CT with contrast: assesses deep lobe tumors, bony invasion, nodal disease. MRI with gadolinium: superior soft tissue detail; evaluates perineural spread (adenoid cystic carcinoma). PET-CT: for staging high-grade malignancies.
Fine Needle Aspiration (FNA)
Sensitivity 85-95%, specificity 95-100% for distinguishing benign from malignant. Milan System for Reporting Salivary Gland Cytopathology: standardized reporting categories (non-diagnostic, non-neoplastic, atypia of undetermined significance, benign, SUMP, suspicious, malignant). Core needle biopsy may be considered when FNA is non-diagnostic.
Staging (AJCC 8th Edition)
Based on tumor size, extraparenchymal extension, and involvement of adjacent structures. T1: <=2 cm, T2: 2-4 cm, T3: >4 cm or extraparenchymal extension, T4a/b: skin, mandible, ear canal, facial nerve, skull base invasion. Nodal staging follows standard head and neck N classification. High-grade histology is the most important prognostic factor independent of stage.
Management Principles
Benign tumors: surgical excision (superficial or total parotidectomy with facial nerve preservation). Malignant tumors: surgery with appropriate margins +/- neck dissection +/- adjuvant radiation. Facial nerve: preserved unless directly invaded by tumor. Adjuvant radiation: indicated for high-grade histology, close/positive margins, perineural invasion, T3-T4, nodal disease. Chemotherapy: limited role; reserved for recurrent/metastatic disease. Androgen receptor blockade: emerging role for salivary duct carcinoma.
Key Clinical Pearls
The smaller the gland, the higher the likelihood of malignancy — always biopsy minor salivary gland lesions. Pleomorphic adenomas should be excised, not enucleated, due to pseudopod extensions through the capsule and risk of recurrence. Adenoid cystic carcinoma has a propensity for perineural invasion and late distant metastases; long-term follow-up (15-20 years) is essential. Facial nerve paralysis with a parotid mass is malignancy until proven otherwise. FNA is the initial tissue sampling modality of choice; incisional biopsy of parotid masses should be avoided.
References
- Speight PM, Barrett AW. Salivary gland tumours: diagnostic challenges and an update on the latest WHO classification. Diagn Histopathol. 2020;26(4):147-158.
- Stodulski D, Mikaszewski B, Stankiewicz C. Signs and symptoms of parotid gland carcinoma and their prognostic value. Int J Oral Maxillofac Surg. 2012;41(7):801-806.
- Rossi ED, Wong LQ, Bizzarro T, et al. The Milan System for Reporting Salivary Gland Cytopathology. Cancer Cytopathol. 2018;126(10):757-766.
- Andreasen S, Therkildsen MH, Grauslund M, et al. Salivary gland neoplasms: an overview of the current WHO classification. Head Neck Pathol. 2021;15(2):394-406.