Describe the tumours of the salivary glands.

Salivary Gland Tumours

• Salivary gland tumours are uncommon and histologically diverse.
• Their behaviour is governed by a useful inverse rule of thumb: the smaller the gland, the higher the proportion of tumours that are malignant.
• The rule OF proportions — 80% of salivary tumours arise in the parotid, and 80% of those are benign, and 80% of the benign ones are pleomorphic adenoma — the so-called "rule of 80s"
• By contrast, half of submandibular tumours and the majority of sublingual and minor gland tumours are malignant — so a tumour of the palate (a minor gland site) is treated with far greater suspicion than one of the parotid
• Pleomorphic adenoma (benign mixed tumour) is much the commonest, presenting as a slow-growing, painless, firm, mobile swelling, in the superficial lobe below and in front of the ear, lifting the ear lobe
• Its three important characteristics — it has a pseudocapsule with microscopic pseudopodia extending through it, so simple enucleation leaves tumour behind and recurs; it recurs multifocally and is then very difficult to treat; and it undergoes malignant transformation to carcinoma EX pleomorphic adenoma in 5% over 10 to 15 years — which is why even a benign tumour should be removed
• Its treatment is superficial (or partial) parotidectomy with facial nerve preservation, taking a cuff of normal tissue
• Warthin tumour (adenolymphoma, papillary cystadenoma lymphomatosum) — the second commonest benign tumour, occurring in older men, strongly associated with smoking, arising almost exclusively in the parotid (the tail), and bilateral or multifocal in 10%
• It is the tumour that takes up technetium-99m and appears hot on a pertechnetate scan.
• The malignant tumours:
• Mucoepidermoid carcinoma — the commonest salivary malignancy overall and the commonest in children; graded low, intermediate and high, with behaviour and prognosis varying accordingly
• Adenoid cystic carcinoma — the commonest malignancy of the submandibular and minor glands, and notable for three things: perineural spread, which is characteristic and causes pain and facial palsy; relentless late local recurrence; and late haematogenous metastasis to the lung, sometimes many years later — so 5-year survival looks good while 20-year survival is poor, and follow-up must be lifelong
• Others — acinic cell carcinoma; carcinoma EX pleomorphic adenoma; adenocarcinoma; squamous carcinoma; and lymphoma, particularly in Sjogren syndrome
• The features suggesting malignancy.
• A facial palsy with a parotid lump is never a pleomorphic adenoma
• Investigation — ultrasound with FNAC.
• Never perform an incisional biopsy of a parotid mass.