Salivary Gland Tumours
Salivary gland tumours are uncommon neoplasms most commonly affecting the parotid gland, with pleomorphic adenoma being the most common benign tumour and mucoepidermoid carcinoma the most common malignancy, requiring surgical excision with careful preservation of the facial nerve.
Key Facts
80% of salivary gland tumours arise in the parotid gland; of these, 80% are benign (the '80% rule') Pleomorphic adenoma is the most common salivary gland tumour overall (60-70% of parotid tumours) Mucoepidermoid carcinoma is the most common malignant salivary gland tumour The smaller the gland, the higher the malignancy rate: parotid 20%, submandibular 50%, sublingual/minor glands >80% Facial nerve (CN VII) runs through the parotid; facial nerve palsy with a parotid mass suggests malignancy Investigation: USS + FNA (fine needle aspiration) is first-line; MRI for deep lobe/malignancy assessment Treatment: superficial parotidectomy with facial nerve preservation for benign parotid tumours Warthin tumour (papillary cystadenoma lymphomatosum) is the second most common benign parotid tumour; bilateral in 10%, associated with smoking
Overview
Key Facts
Salivary gland tumours are a heterogeneous group of neoplasms arising from the major (parotid, submandibular, sublingual) or minor salivary glands. The parotid gland is the most commonly affected, and the majority of parotid tumours are benign.
Epidemiology
- Account for 3-6% of all head and neck tumours
- Annual incidence: approximately 2-3 per 100,000
- Peak age: 40-60 years for benign; 60-70 years for malignant
- Equal sex distribution (Warthin tumour: male predominance)
Aetiology
- Mostly unknown aetiology
- Radiation exposure (prior radiotherapy) increases risk of salivary malignancy
- Smoking: associated with Warthin tumour
- EBV: associated with lymphoepithelial carcinoma
- Genetic: PLAG1 rearrangement in pleomorphic adenoma; MAML2 fusion in mucoepidermoid carcinoma
Pathophysiology
- Salivary glands contain diverse cell types (serous, mucous, myoepithelial, ductal) giving rise to varied tumour histology
- Benign tumours: well-encapsulated but may have pseudopod extensions (pleomorphic adenoma)
- Malignant tumours: may invade surrounding structures including facial nerve
- The facial nerve (CN VII) divides the parotid into superficial and deep lobes; most tumours arise in the superficial lobe
- Pleomorphic adenomas have a 5-10% risk of malignant transformation (carcinoma ex pleomorphic adenoma) if left untreated >10-15 years
Clinical Presentation
Benign Tumours
- Slow-growing, painless, firm, mobile lump in the parotid, submandibular, or palatal region
- Intact facial nerve function
- May have been present for months to years
Malignant Tumours
- Rapid growth
- Pain (nerve invasion)
- Facial nerve palsy (highly suspicious for malignancy in parotid mass)
- Fixation to skin or deep structures
- Cervical lymphadenopathy
- Trismus (deep lobe extension)
Red Flags
- Facial nerve palsy with parotid mass
- Rapidly enlarging salivary gland mass
- Hard, fixed mass
- Skin invasion or ulceration
- Cervical lymphadenopathy
- Pain/paraesthesia
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Pleomorphic adenoma | Slow-growing, painless, parotid, firm | USS, FNA, MRI |
| Warthin tumour | Bilateral (10%), soft/fluctuant, smoker, male | USS, FNA, Tc-99m scan (hot) |
| Mucoepidermoid carcinoma | Most common malignant; variable grade | FNA, MRI, biopsy |
| Adenoid cystic carcinoma | Perineural invasion, pain, slow growth, late metastases | MRI, biopsy |
| Lymphoma | Bilateral parotid swelling, B symptoms | Excision biopsy, CT |
| Sialadenitis/sialolithiasis | Pain, swelling with meals, palpable stone | USS, sialography |
Diagnosis / Investigation
Bedside
- Thorough head and neck examination
- Facial nerve function assessment (House-Brackmann grading)
- Bimanual palpation (submandibular, floor of mouth)
Bloods
- Not routinely diagnostic
- FBC, LDH if lymphoma suspected
Imaging
- USS: first-line imaging; assesses size, solid/cystic nature, guides FNA
- MRI: superior for deep lobe parotid tumours, perineural spread, and malignancy assessment
- CT neck with contrast: for suspected malignancy staging, bony invasion
- PET-CT: for staging of high-grade malignancy
Special Tests
- FNA cytology (USS-guided): first-line tissue diagnosis; sensitivity 80-90% for distinguishing benign from malignant
- Core biopsy: if FNA non-diagnostic
- Incisional biopsy is AVOIDED for parotid tumours (risk of tumour seeding, facial nerve damage)
- Histopathology of excised specimen: definitive diagnosis
Management
Non-pharmacological
- All salivary gland tumours require surgical excision for definitive diagnosis and treatment
- MDT discussion for malignant tumours
Surgical
- Superficial parotidectomy: for benign parotid tumours in superficial lobe
- Careful identification and preservation of facial nerve
- Recurrence rate: <5% for pleomorphic adenoma
- Total conservative parotidectomy: for deep lobe tumours or malignancy (nerve preserved if not invaded)
- Radical parotidectomy: sacrifice of facial nerve if invaded by tumour
- Submandibular gland excision: for submandibular tumours
- Neck dissection: for confirmed cervical lymph node metastasis
- Nerve grafting: if facial nerve sacrificed (great auricular or sural nerve graft)
Adjuvant Treatment
- Radiotherapy: for high-grade malignancy, positive margins, perineural invasion, adenoid cystic carcinoma, recurrence
- Neutron therapy: historically for adenoid cystic carcinoma
- Chemotherapy has limited role in salivary gland malignancy
Referral Criteria
- 2-week wait referral: any unexplained salivary gland mass >3 weeks
- Urgent ENT: facial nerve palsy with salivary gland mass
- MDT: all malignant salivary gland tumours
Prognosis
- Pleomorphic adenoma: excellent prognosis; recurrence <5% after adequate excision; 5-10% risk of malignant transformation if untreated >10-15 years
- Warthin tumour: excellent; rarely recurs; bilateral in 10%
- Mucoepidermoid carcinoma: variable; low-grade >90% 5-year survival; high-grade 30-50%
- Adenoid cystic carcinoma: tendency for perineural invasion and late distant metastases (lung); 5-year survival 60-70% but 15-year survival 20-30%
- Acinic cell carcinoma: generally favourable; >80% 5-year survival
- Complications of parotid surgery: temporary facial nerve weakness (10-20%), permanent palsy (<3%), Frey syndrome (gustatory sweating, 30-50%), salivary fistula
Other Relevant Information
The 80% Rule of Salivary Gland Tumours
| Rule | Detail |
|---|---|
| 80% arise in parotid | Parotid is the most common site |
| 80% of parotid tumours are benign | Most common: pleomorphic adenoma |
| 80% of parotid tumours are in superficial lobe | Deep lobe tumours are less common |
| Malignancy rate increases with smaller glands | Parotid 20%, submandibular 50%, minor glands >80% |
Classification of Salivary Gland Tumours
| Type | Examples |
|---|---|
| Benign | Pleomorphic adenoma, Warthin tumour, oncocytoma |
| Low-grade malignant | Low-grade mucoepidermoid, acinic cell, polymorphous adenocarcinoma |
| High-grade malignant | High-grade mucoepidermoid, adenoid cystic, salivary duct carcinoma, carcinoma ex pleomorphic adenoma |
Complications of Parotid Surgery
| Complication | Incidence | Detail |
|---|---|---|
| Temporary facial nerve weakness | 10-20% | Usually recovers in weeks-months |
| Permanent facial nerve palsy | <3% | Higher in malignancy, revision surgery |
| Frey syndrome | 30-50% | Gustatory sweating (aberrant reinnervation) |
| Greater auricular nerve numbness | Common | Numbness of ear lobe |
| Salivary fistula | 5% | Usually self-resolving |