Pleomorphic Adenoma

Pleomorphic adenoma (benign mixed tumour) is the commonest salivary gland neoplasm, accounting for about 60 to 70 percent of parotid, 50 percent of submandibular, and about 40 to 50 percent of minor salivary gland tumours. Annual incidence is about 2.5 to 3.5 per 100 000, with a peak at ages 30 to 60 years and female predominance. About 80 percent arise in the superficial lobe of the parotid.

The tumour is composed of epithelial and myoepithelial cells in a myxoid, chondroid or fibrous stroma, hence "pleomorphic". It is enclosed in a thin, incomplete pseudocapsule with tumour projections (pseudopodia) that penetrate the capsule; simple enucleation therefore leaves residual tumour, causing recurrence in 20 to 45 percent. Genetic alterations involve PLAG1 and HMGA2 rearrangements. Growth is slow (about 1 to 2 cm per year).

Malignant transformation to carcinoma ex pleomorphic adenoma occurs in about 1 to 6 percent (risk rising to 10 percent or more after 15 years), with the risk higher in long standing or recurrent tumours. Recurrent tumours are multinodular and can spread throughout the operative bed.

• Slowly enlarging, painless, firm, mobile, smooth or lobulated lump in the parotid (in front of or below the ear, behind the angle of the mandible), submandibular triangle, or palate (submucosal dome).
• No facial nerve weakness in benign tumours; no pain, no skin fixation.
• Deep lobe tumours: parapharyngeal swelling with medial displacement of the tonsil, dysphagia, snoring, and a swelling at the oropharynx.
• Palatal tumours: firm submucosal mass without ulceration.
• Recurrent: multiple nodules in the scar.
• Red flags (malignant change): rapid growth after a long quiet period, pain, facial nerve palsy, skin or deep fixation, ulceration, cervical lymphadenopathy.

• Clinical examination of the face, facial nerve function (House-Brackmann grade), oral cavity, oropharynx, neck.
• Ultrasound with fine needle aspiration cytology (FNAC) as the first line: lobulated, well defined, hypoechoic mass; cytology shows fibrillary chondromyxoid stroma with epithelial and myoepithelial cells (sensitivity above 90 percent, but diagnostic accuracy less for malignancy); core needle biopsy where FNAC is non-diagnostic.
• MRI with contrast: well defined, lobulated T2 hyperintense mass with a hypointense capsule, high apparent diffusion coefficient; used to evaluate deep lobe extension, recurrence, and signs of malignancy (irregular margins, low T2 signal).
• CT for bone involvement and parapharyngeal tumours.
• Frozen section is not routinely used.
• Exclude Warthin tumour, basal cell adenoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, lymphoma, lymph node, cyst, and lipoma.

• Surgical excision is the definitive treatment: superficial parotidectomy with facial nerve identification and preservation (the nerve trunk is found by landmarks: tragal pointer, tympanomastoid suture, posterior belly of digastric) for superficial lobe tumours; extracapsular dissection for small mobile superficial tumours in experienced hands; total conservative parotidectomy for deep lobe tumours.
• Submandibular tumours: excision of the whole gland, protecting the marginal mandibular, lingual and hypoglossal nerves.
• Palatal and minor gland tumours: wide local excision including the periosteum, with tumour free margins of about 5 mm.
• Parapharyngeal tumours: transcervical transparotid approach, with mandibulotomy for large tumours.
• Avoid enucleation; avoid tumour spillage (spillage carries a recurrence of up to 20 to 30 percent).
• Perioperative: cefazolin 1 g intravenously at induction (clean contaminated wounds), single dose; suction drain for 24 to 48 hours; analgesia with paracetamol 1 g every 6 hours and ibuprofen 400 mg every 8 hours.
• Complications: transient facial weakness (10 to 40 percent), permanent facial nerve injury (under 2 percent), Frey syndrome (gustatory sweating, 10 to 40 percent; treat with intradermal botulinum toxin A 2 to 3 units per cm2), sialocele, great auricular nerve numbness, scar.
• Recurrent tumours: re-excision with a wide margin and facial nerve preservation; consider adjuvant radiotherapy 60 Gy in 30 fractions for multifocal recurrence, positive margins or spillage.
• Carcinoma ex pleomorphic adenoma: wide excision with neck dissection and radiotherapy 60 to 66 Gy.
• Follow up: yearly clinical review for at least 5 to 10 years, ultrasound or MRI if recurrence is suspected; recurrence can appear after 20 years.
• Counselling: benign but must be excised because of growth and malignant potential; discuss facial nerve risk.