Benign Salivary Gland Tumours

Benign salivary gland tumours are non-malignant neoplasms of the major and minor salivary glands. Pleomorphic adenoma is by far the commonest specific type across all salivary gland sites, followed by Warthin tumour (adenolymphoma).

Both arise predominantly, though not exclusively, in the parotid gland. The parotid harbours the great majority of salivary gland tumours overall, and most parotid tumours are benign.

Tumours of the submandibular and minor salivary glands are proportionally less common but carry a substantially higher relative likelihood of malignancy. This general principle informs clinical risk assessment and patient counselling from first presentation.

Classification and pathophysiology

• Pleomorphic adenoma is the commonest benign salivary gland tumour overall. It arises predominantly in the superficial lobe of the parotid gland.
• Histologically it is a variable mixture of epithelial and myoepithelial elements within a myxoid or chondroid stroma, which gives the pleomorphic, mixed architecture behind its name.
• It characteristically shows capsular irregularity and microscopic tumour extension beyond the grossly visible capsule. This directly affects the surgical approach needed to minimise recurrence risk.
• Warthin tumour (papillary cystadenoma lymphomatosum) is the second commonest benign parotid tumour. It arises almost exclusively in the parotid gland, probably from salivary gland tissue entrapped within intraparotid or periparotid lymph nodes during embryological development.
• Warthin tumour has a strong, well established association with smoking. It presents bilaterally or multifocally in a meaningful proportion of patients, an important epidemiological difference from pleomorphic adenoma.
• Pleomorphic adenoma carries a recognised, generally low, risk of malignant transformation over time (carcinoma ex pleomorphic adenoma). The risk increases with the duration the tumour has been present.
• This is a specific rationale for excising confirmed pleomorphic adenoma rather than observing it indefinitely, even without other concerning features.

• The characteristic presentation across the benign salivary gland tumour spectrum is a slowly growing, painless, mobile mass within the parotid or, less commonly, another salivary gland.
• The mass is typically present for a prolonged period, sometimes years, before presentation, reflecting slow, indolent growth.
• Facial nerve function is characteristically entirely normal in benign parotid tumours. Any facial nerve weakness is a significant red flag, strongly suggesting malignant transformation or a primary malignant tumour. It warrants urgent further assessment.
• Warthin tumour characteristically presents in older patients with a significant smoking history. It may feel soft and cystic on examination, reflecting its cystic architecture.
• Look specifically for bilateral or multiple lesions, because Warthin tumour has a recognised tendency toward multifocal presentation.
• Pleomorphic adenoma of long standing duration should raise concern for possible malignant transformation, as should a recent change in growth rate, pain or facial nerve involvement. These warrant prompt further assessment rather than continued observation.

• Ultrasound with fine needle aspiration cytology is the standard initial diagnostic approach for any parotid or other salivary gland mass. It characterises the lesion and supports preoperative risk stratification.
• Pleomorphic adenoma and Warthin tumour each show characteristic, though not entirely infallible, cytological features.
• Magnetic resonance imaging gives superior soft tissue characterisation. It is particularly valuable for larger lesions, deep lobe parotid tumours, or any clinical or cytological suspicion of malignancy.
• It supports preoperative assessment of tumour extent and its relationship to the facial nerve and adjacent structures, which directly informs surgical planning.
• Definitive diagnosis rests on formal histopathology of the excised specimen. Fine needle aspiration cytology alone cannot reliably distinguish certain benign from low grade malignant salivary gland tumour subtypes in every case.

• Surgical excision is the standard, definitive treatment for confirmed or strongly suspected pleomorphic adenoma. Fine needle aspiration cytology alone leaves diagnostic uncertainty, and prolonged observation carries a recognised, low risk of malignant transformation.
• For parotid lesions, perform superficial parotidectomy or, for deep lobe lesions, total parotidectomy. Identify and preserve the facial nerve meticulously throughout its course within the gland.
• Generally avoid enucleation alone (simple removal of the tumour without a surrounding margin of normal gland tissue) for pleomorphic adenoma. Because of capsular irregularity and microscopic tumour extension, it carries a substantially higher recurrence rate than formal parotidectomy with an adequate margin of normal tissue.
• Warthin tumour is also managed with surgical excision, generally by superficial parotidectomy. For smaller, well localised lesions, a more limited partial superficial parotidectomy may be used.
• Warthin tumour is less locally infiltrative, which sometimes supports a less extensive operation than pleomorphic adenoma. Formal excision rather than simple aspiration or observation remains the standard.
• Provide regular, structured follow up after excision. Monitor for recurrence and for surgical complications, particularly facial nerve function.
• Frey syndrome is a recognised risk after parotid surgery. This gustatory sweating results from aberrant reinnervation of the parotid skin flap by parasympathetic salivary fibres, after surgical division and regeneration of the nerve fibres.