Parotid Gland Tumours
ENT · Head & Neck · lean revision notes
Parotid Gland Tumours
The parotid is the commonest site of salivary gland neoplasia, and the parotid is also where the majority of tumours are benign. This topic is a perennial NEET PG favourite because it blends anatomy (facial nerve, retromandibular vein), pathology (pleomorphic adenoma vs Warthin vs malignancies), and surgery (parotidectomy, Frey syndrome). Get the comparisons and the "rule of 80s" right and you can answer almost any stem.
The "Rule of 80s" — the framing fact
High-yield: ~80% of salivary tumours arise in the parotid; ~80% of parotid tumours are benign; ~80% of benign parotid tumours are pleomorphic adenoma; ~80% of pleomorphic adenomas occur in the superficial lobe.
The smaller the gland, the higher the chance of malignancy. Therefore:
| Gland | Frequency of tumours | Proportion malignant |
|---|---|---|
| Parotid | Highest (~70–80%) | ~20–25% malignant |
| Submandibular | Intermediate (~10–15%) | ~40–50% malignant |
| Sublingual | Rare | ~70–90% malignant (almost always malignant) |
| Minor salivary glands (palate) | ~10% | ~50% malignant; adenoid cystic common |
High-yield: A tumour in the sublingual gland or minor salivary glands of the floor of mouth should be assumed malignant until proven otherwise. The palate is the commonest intra-oral site for minor salivary gland tumours.
Surgical anatomy you must know
The facial nerve (CN VII) divides the parotid into a superficial lobe (~80% of bulk) and a deep lobe. The nerve does NOT lie in a true anatomical plane but defines a surgical plane. Structures within the gland from superficial to deep:
Facial nerve → retromandibular vein → external carotid artery (mnemonic: the vein is between the nerve and artery; nerve most superficial, artery deepest).
Landmarks for identifying the facial nerve trunk during surgery:
- Tragal pointer — nerve lies ~1 cm deep and inferior to its tip.
- Tympanomastoid suture — nerve is ~6–8 mm deep to it (most reliable bony landmark).
- Posterior belly of digastric — nerve at the same depth as its upper border.
- Retrograde identification via a peripheral branch (e.g. marginal mandibular) when the trunk is obscured.
High-yield: The deep-lobe tumour presenting in the parapharyngeal space can push the tonsil/soft palate medially — a "dumbbell" or iceberg tumour via the stylomandibular tunnel.
Classification of parotid tumours
| Benign | Malignant |
|---|---|
| Pleomorphic adenoma (most common overall) | Mucoepidermoid carcinoma (most common malignant overall & in children) |
| Warthin tumour (papillary cystadenoma lymphomatosum) | Adenoid cystic carcinoma (most common in submandibular/minor glands; perineural) |
| Oncocytoma | Acinic cell carcinoma |
| Basal cell adenoma | Carcinoma ex-pleomorphic adenoma |
| Canalicular adenoma | Adenocarcinoma, squamous cell carcinoma |
1. Pleomorphic adenoma (benign mixed tumour)
The commonest salivary neoplasm. "Pleomorphic" refers to varied histological architecture, not cellular pleomorphism.
- Cell of origin: myoepithelial + epithelial cells; produces a characteristic chondromyxoid (cartilage-like) stroma.
- Clinical: slow-growing, painless, firm, mobile lump at the angle of the jaw; commonest in 4th–5th decade, slight female predominance.
- Pseudocapsule: incomplete capsule with tumour pseudopodia/satellite nodules projecting through it.
High-yield: Because of pseudopodia through the pseudocapsule, enucleation leads to high recurrence. Treatment is superficial parotidectomy (or partial/extracapsular dissection) with a cuff of normal tissue, preserving the facial nerve.
- Malignant transformation: carcinoma ex-pleomorphic adenoma — risk rises with duration (long-standing tumour, >10–15 years) and with recurrence. Suspect if a long-standing lump suddenly enlarges, becomes fixed, painful, or develops facial palsy.
2. Warthin tumour (papillary cystadenoma lymphomatosum / adenolymphoma)
- Almost exclusively in the parotid (tail), arising from heterotopic salivary ducts within intra-parotid lymph nodes — hence lymphoid stroma.
- Demographics: older men, strong association with smoking.
High-yield: Warthin tumour is the only common bilateral/multicentric parotid tumour (~10%). It is the salivary tumour that is "hot" (takes up tracer) on ⁹⁹ᵐTc-pertechnetate scan because of abundant oncocytes/mitochondria. Malignant transformation is rare.
- Histology: double-layered oncocytic epithelium with papillary cystic spaces over a dense lymphoid stroma with germinal centres.
3. Mucoepidermoid carcinoma (MEC)
- Most common malignant salivary tumour overall and the most common salivary malignancy in children.
- Mixture of mucous + epidermoid (squamoid) + intermediate cells.
- Associated with MAML2 / CRTC1–MAML2 gene rearrangement.
- Grading drives prognosis: low grade (more mucous cells, cystic, good prognosis) → high grade (more solid/epidermoid, behaves aggressively).
4. Adenoid cystic carcinoma (cylindroma)
- Most common malignancy of submandibular, sublingual and minor salivary glands; also a common malignant parotid tumour.
- Cribriform "Swiss-cheese" pattern on histology.
High-yield: Adenoid cystic carcinoma is notorious for perineural invasion → pain and facial nerve palsy early, "skip" lesions along nerves, and late distant metastasis to lung (haematogenous) with a paradoxically good 5-year but poor 15–20-year survival.
5. Acinic cell carcinoma
- Low-grade malignancy; serous acinar differentiation; can be bilateral; relatively good prognosis.
Benign vs malignant — clinical discriminators
| Feature | Favours benign | Favours malignant |
|---|---|---|
| Growth | Slow | Rapid / sudden change |
| Pain | Usually absent | Present |
| Facial nerve | Intact | Palsy = malignancy until proven otherwise |
| Mobility | Mobile | Fixed to skin/deep tissue |
| Skin | Normal | Ulceration, infiltration |
| Cervical nodes | Absent | Present (metastasis) |
| Consistency | Firm, smooth | Hard, irregular |
High-yield: Facial nerve palsy with a parotid mass = malignancy (or carcinoma ex-pleomorphic). Benign tumours, even large ones, virtually never cause facial palsy — they displace the nerve, not infiltrate it.
Diagnosis & investigation of choice
Stepwise approach:
History & examination (bimanual palpation, facial nerve assessment) → FNAC → imaging (MRI > CT) → definitive surgery with histopathology.
- FNAC (fine-needle aspiration cytology): investigation of first choice for a parotid lump. Safe, no risk of facial nerve injury, no tumour seeding (unlike core/incisional biopsy of pleomorphic adenoma).
High-yield: Incisional/open biopsy of a parotid mass is contraindicated — risk of tumour spillage (pleomorphic adenoma seeding) and facial nerve injury. Use FNAC instead.
- Imaging of choice — MRI: best soft-tissue detail, defines deep-lobe and parapharyngeal extension, perineural spread, and relation to facial nerve. CT is useful for bony invasion. Ultrasound guides FNAC and assesses superficial lesions.
- ⁹⁹ᵐTc-pertechnetate scintigraphy: classically "hot" in Warthin tumour and oncocytoma (most other tumours are cold). A favourite single-best-answer.
- Sialography: largely historical; shows "ball-in-hand"/filling defect — not for routine tumour workup.
Management & drug/treatment of choice
Surgery is the mainstay; there is no useful chemotherapy for routine cure.
| Scenario | Operation of choice |
|---|---|
| Superficial-lobe benign tumour (e.g. pleomorphic adenoma) | Superficial parotidectomy with facial nerve preservation |
| Deep-lobe tumour | Total conservative parotidectomy (preserving nerve) |
| Malignant, low grade, nerve uninvolved | Parotidectomy + nerve preservation |
| Malignant, high grade or nerve involved | Radical parotidectomy ± facial nerve sacrifice + neck dissection + post-op radiotherapy |
| Warthin tumour | Superficial parotidectomy / partial parotidectomy (low recurrence) |
Key surgical principles:
- Identify and preserve the facial nerve wherever oncologically safe.
- Adjuvant radiotherapy for high-grade malignancy, positive margins, perineural invasion (esp. adenoid cystic), or recurrence.
- Sacrificed facial nerve → consider immediate cable grafting (great auricular or sural nerve graft).
High-yield: Adenoid cystic carcinoma needs wide excision + post-operative radiotherapy because of perineural spread; margins are notoriously hard to clear.
Complications of parotid surgery
- Facial nerve injury — transient weakness common (neuropraxia from traction); permanent palsy if nerve transected. Marginal mandibular branch most often injured (asymmetry of lower lip).
- Frey syndrome (gustatory sweating, auriculotemporal syndrome).
- Greater auricular nerve injury → numbness of the earlobe (commonest sensory deficit).
- Salivary fistula / sialocele — usually self-limiting.
- Haematoma, infection, hypertrophic/keloid scar.
- First-bite syndrome — pain in the parotid region with the first bite of a meal (after deep-lobe/parapharyngeal surgery).
- Cosmetic hollowing at the operative site.
Frey syndrome — a guaranteed exam topic
High-yield: Frey syndrome = gustatory sweating and flushing over the pre-auricular/cheek skin while eating. It results from aberrant regeneration of damaged parasympathetic (secretomotor) auriculotemporal nerve fibres onto the sympathetic receptors of the skin's sweat glands and cutaneous vessels.
- Diagnosis: Minor's starch-iodine test — iodine + starch painted on cheek turns blue-black where sweating occurs on tasting.
- Prevention: interposition of a barrier at surgery (e.g. sternocleidomastoid muscle flap, temporoparietal fascia, AlloDerm).
- Treatment of choice: botulinum toxin injection into affected skin (blocks acetylcholine release); topical anticholinergics (glycopyrrolate) and antiperspirants are alternatives.
Key differentials of a parotid swelling
| Differential | Distinguishing clue |
|---|---|
| Pleomorphic adenoma | Firm, mobile, slow, single, FNAC chondromyxoid stroma |
| Warthin tumour | Older male smoker, bilateral, hot on Tc-99m |
| Mucoepidermoid carcinoma | Commonest malignancy; FNAC mucous+epidermoid cells |
| Adenoid cystic carcinoma | Pain, nerve palsy, perineural; cribriform |
| Parotid abscess / sialadenitis | Acute, painful, tender, fever; pus from duct |
| Sialolithiasis | Mealtime swelling & pain (more common in submandibular/Wharton's duct) |
| Sjögren syndrome / MALT | Bilateral diffuse enlargement, dry eyes/mouth, autoantibodies |
| Lymphoma / sarcoidosis / HIV (lymphoepithelial cysts) | Diffuse, bilateral, systemic features |
| Pre-auricular lymph node, sebaceous cyst, lipoma | Superficial, separate from gland |
High-yield: Sialolithiasis is far commoner in the submandibular gland (Wharton's duct) because its secretions are mucinous/alkaline and the duct runs uphill; tumours are commoner in the parotid. Classic discriminator stem.
Recently asked / exam angle
- Single-best-answer staples: "Most common salivary gland tumour?" → pleomorphic adenoma. "Most common malignant salivary tumour?" → mucoepidermoid carcinoma. "Most common malignant tumour of submandibular/minor glands?" → adenoid cystic carcinoma.
- Image/clinical vignette: older male smoker, bilateral parotid lump, hot on technetium scan → Warthin tumour.
- Mechanism question: gustatory sweating after parotidectomy and its nerve (auriculotemporal, parasympathetic misdirection) → Frey syndrome; test = Minor's starch-iodine; Rx = botulinum toxin.
- Anatomy: structure dividing superficial and deep lobes (facial nerve); order of structures (nerve → retromandibular vein → external carotid artery); landmark to find nerve trunk (tympanomastoid suture / tragal pointer).
- Surgery: why enucleation of pleomorphic adenoma is wrong (pseudopodia → recurrence) → superficial parotidectomy.
- Red flag: parotid mass + facial palsy → malignant.
- Perineural invasion is the buzzword pointing to adenoid cystic carcinoma; chondromyxoid stroma → pleomorphic adenoma; cribriform/Swiss-cheese → adenoid cystic; lymphoid stroma with oncocytes → Warthin.
- MAML2 rearrangement → mucoepidermoid carcinoma (newer molecular MCQ).
Rapid revision
- Rule of 80s: 80% salivary tumours in parotid; 80% of those benign; 80% benign are pleomorphic adenoma; 80% in superficial lobe.
- Smaller the gland, higher the malignancy risk — sublingual/minor glands mostly malignant.
- Pleomorphic adenoma = commonest; chondromyxoid stroma; enucleation → recurrence; do superficial parotidectomy.
- Warthin tumour = older male smoker, bilateral, hot on Tc-99m, lymphoid stroma; parotid-only.
- Mucoepidermoid carcinoma = commonest salivary malignancy and commonest in children; MAML2 rearrangement.
- Adenoid cystic carcinoma = commonest in submandibular/minor glands; perineural invasion, cribriform pattern, late lung mets.
- Facial nerve palsy + parotid mass = malignancy until proven otherwise.
- Facial nerve divides superficial and deep lobes; order = nerve → retromandibular vein → external carotid artery.
- FNAC is the investigation of choice; open biopsy is contraindicated; MRI is the imaging of choice.
- Frey syndrome = gustatory sweating via auriculotemporal nerve; Minor's starch-iodine test; treat with botulinum toxin.
- Commonest sensory deficit after parotidectomy = greater auricular nerve (earlobe numbness).
- Carcinoma ex-pleomorphic adenoma: suspect when an old lump suddenly grows, pains, or causes palsy.