Pleomorphic Adenoma (Benign Mixed Tumour)
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Direct answer
Roughly three of every five salivary gland neoplasms are pleomorphic adenomas — the benign mixed tumour, a painless, slow-growing, firm and mobile lump, overwhelmingly of the parotid's superficial lobe, that couples epithelial and myoepithelial cells with a chondromyxoid (cartilage-like) stroma to produce its famous pleomorphic histology. It is pseudoencapsulated: satellite tumour buds and capsular dehiscences mean that simple enucleation shells out a seed-bed of recurrence, which is why superficial parotidectomy with formal facial nerve dissection is the standard even for a small tumour. Malignant transformation after decades — carcinoma ex-pleomorphic adenoma — is heralded by sudden rapid growth, pain or facial weakness. Intraorally it is the commonest palatal minor gland tumour, presenting as a smooth submucosal dome, and complete excision with the capsule intact cures it.
What you must remember
- Frequency: about 60 per cent of all salivary gland tumours and the large majority of parotid neoplasms; commonest in the third to sixth decades with a female predominance; the commonest intraoral site is the palate, then upper lip and buccal mucosa.
- Clinical identity: painless, slow (years), firm, lobulated, mobile lump in the pre-auricular or retromandibular region; facial nerve function is intact — weakness, fixity, pain or rapid growth all argue against benignity.
- Histology: sheets, tubules and islands of epithelial and myoepithelial cells suspended in a metachromatic chondromyxoid stroma; plasmacytoid (hyaline) myoepithelial cells are a recognisable constituent; mesenchymal-like cartilage and bone may form.
- The capsule paradox: the capsule is variable, incomplete and breached by satellite nodules — the histological fact that forbids enucleation and explains multinodular recurrences.
- Surgery: superficial parotidectomy with nerve identification and preservation for superficial-lobe tumours; extracapsular dissection only in selected favourable cases in experienced hands; intraoral lesions are excised with a cuff of normal tissue, sometimes needing palatal bone.
- Recurrence: multinodular and late after enucleation or rupture, and the second operation works on a scarred, nerve-encased field.
- Malignant potential: carcinoma ex-pleomorphic adenoma, typically after 15 or more years of a stable lump, with sudden enlargement, pain, nerve palsy or skin invasion; carcinoma in situ within a pleomorphic adenoma is the earliest expression; metastasizing and non-invasive variants also exist in the family.
A parotid lump worked end to end
A 44-year-old teacher notices a lump in front of her right ear for two years, unchanged and painless. Step one, clinical mapping: firm, lobulated, mobile, about 2.5 centimetres, in the typical superficial-lobe latitude below and in front of the tragus; facial nerve function full, no cervical nodes, no skin changes — clinically a benign tumour, pleomorphic adenoma leading the differential ahead of Warthin tumour. Step two, imaging: ultrasound with fine needle aspiration cytology reporting the benign mixed tumour pattern of epithelial strands in chondromyxoid matrix. Step three, the operation: superficial parotidectomy with identification of the trunk of the facial nerve and dissection off its branches, delivering the tumour with an intact capsule and a rim of normal parotid — enucleation is refused specifically because of satellite buds and capsule dehiscence. Step four, histology confirms the diagnosis, margins clear. Step five, counselling: annual review, because recurrence is late and multinodular, and sudden growth, pain or facial weakness after decades of quiescence demands urgent re-biopsy for carcinoma ex-pleomorphic adenoma.
Where examiners set the trap
The single most examined fact is why not enucleate: answers must invoke the incomplete capsule and satellite nodules histologically, then the multinodular recurrence clinically, then the scarred nerve at reoperation — a chain of consequence, not just a rule. The second trap is the intraoral palatal swelling: smooth, dome-shaped, submucosal, slow — students default to a cyst or vascular lesion, forgetting that the palate is the commonest minor gland site and pleomorphic adenoma the commonest tumour there; a biopsy settles it and excision includes periosteum or bone as needed. The third is depth of malignant-transformation knowledge: naming carcinoma ex-pleomorphic adenoma earns one mark, describing its warning signs — sudden growth, pain, facial palsy after 15-plus years — earns the next. Finally, Warthin tumour makes the standard comparison: an older man, smoker, cystic, parotid tail, lymphoid stroma with oncocytic epithelium, bilateral in a minority.
Frequently asked questions
Why is enucleation of a parotid pleomorphic adenoma condemned?
The tumour's capsule is incomplete and breached by satellite nodules, so shelling it out leaves tumour buds that recur in a multinodular pattern around a scarred facial nerve.
What two components create the "mixed" histology?
Epithelial and myoepithelial cells arranged in ducts, sheets and plasmacytoid clusters, embedded in a metachromatic chondromyxoid stroma that mimics cartilage.
Which clinical changes suggest malignant transformation?
Sudden rapid growth of a long-standing lump, new pain, facial nerve weakness or skin fixation — the cardinal signs of carcinoma ex-pleomorphic adenoma.
What is the standard operation for a superficial-lobe tumour?
Superficial parotidectomy with identification and preservation of the facial nerve, removing the tumour with its capsule and a rim of normal parotid tissue.
Which is the commonest intraoral site?
The palate, treated by complete excision including periosteum or palatal bone as required.