Pleomorphic Adenoma

🧬 Pleomorphic Adenoma

📌 Definition of Pleomorphic Adenoma

Pleomorphic adenoma is a biphasic (mixed) tumour composed of epithelial and mesenchyme like (stromal) elements forming a variable myxoid, chondroid, osseous or adipose stroma.

What features make pleomorphic adenoma "pleomorphic"?

Which cell types form the epithelial component?

Which is the most common benign salivary gland tumour?

What is the most common site of pleomorphic adenoma?

• Age / Sex: 4th–6th decade (peak ~6th decade); female preponderance.

• Malignant transformation (Carcinoma ex-pleomorphic adenoma) risk ≈ 1–5% after long duration (~≥10 years).

🔬 Histogenesis of Pleomorphic Adenoma

1. Dardick’s Theory

   • Origin from intercalated duct reserve cells (pluripotent epithelial progenitors).

   • Myoepithelial cells → undergo mesenchymal metaplasia → produce myxoid / chondroid / osseous / adipose stromal elements.

   • Implies purely epithelial origin with stromal elements being myoepithelial derived (mesenchyme like, not true mesenchyme).

2. Willis’ Theory

   • Tumour arises from both epithelial and mesenchymal elements → true mixed tumour (stromal elements are true mesenchyme).

3. Genetic Evidence

   • Chromosomal rearrangements reported (e.g., 8q12 PLAG1, 12q13-15 HMGA family) - support a clonal epithelial origin with myoepithelial plasticity.

🗺️ Sites & Epidemiology of Pleomorphic Adenoma

• Parotid — ≈85% (superficial lobe ~80% of parotid cases; deep lobe ~10%).
• Submandibular — ≈8% of pleomorphic adenomas.
• Minor salivary glands — ≈7% (palate commonest).

🧾 Gross Pathology of Pleomorphic Adenoma

• Appearance: Irregular–ovoid, well-circumscribed mass; cut surface fleshy, rubbery or glistening, tan-white.

• Capsule: Thin fibrous capsule (may be incomplete); minor gland lesions often unencapsulated.

• Pseudopodia: Tumour projections into adjacent gland (pseudopods) — important cause of recurrence if incompletely excised.

• Areas of haemorrhage/infarction may be seen.

🔬 Microscopy of Pleomorphic Adenoma

Epithelial component

• Ductal structures: cuboidal/columnar/oncocytic lining.

• Solid nests, sheets, cords, trabeculae may be present.

Myoepithelial component

• Highly variable: spindle, plasmacytoid (plasmacytoid/epithelioid), clear cell forms.

• Myoepithelial cells are key to stromal diversity.

Stromal / Mesenchyme-like component

• Myxoid (most common), chondroid, osseous, adipose — degree/type of stroma determines tumour firmness.

🚩 Presence of cartilage/bone or calcification in a salivary mass is suggestive of pleomorphic adenoma.

🩺 Clinical Features of Pleomorphic Adenoma

• Presentation: Single, slow-growing, painless, smooth, lobulated, mobile swelling - classically just below and in front of the ear (parotid region).

• Positive curtain sign

• Ear lobule elevation may be seen with superficial parotid tumours.

• Deep lobe lesions: present as intraoral / parapharyngeal swelling (medial displacement of tonsil / oropharyngeal wall) → dysphagia, stertor, voice change.

• Facial nerve involvement is rare in benign pleomorphic adenoma - if present suspect malignancy.

What is Positive curtain sign?

🚩 Red Flags for Carcinoma ex Pleomorphic Adenoma

• Recent rapid increase in size

• Pain

• Fixity to skin / deep structures

• Ulceration / skin infiltration

• Facial nerve palsy

• Nodularity / irregularity

• Regional lymphadenopathy

• Restricted jaw movement

🧪 Investigations of Pleomorphic Adenoma

1. Ultrasound

2. FNAC (Fine Needle Aspiration Cytology)

3. MRI - Gold standard for soft tissue

4. CT - helpful for bony detail or if MRI contraindicated.

5. Core biopsy - generally avoided (risk of seeding, facial nerve injury); reserved if FNAC inconclusive and results will change management.

6. Scintigraphy (Tc-99m pertechnetate) — not routine for pleomorphic adenoma (more useful for Warthin’s tumour).

What is the first line imaging done in Pleomorphic Adenoma?

What are the indications of MRI in Pleomorphic Adenoma?

🛠 Treatment of Pleomorphic Adenoma

• Surgery is the treatment of choice

• No role for radiotherapy/chemotherapy in primary benign disease.

1️⃣ Parotid

• Enucleation → obsolete (high recurrence due to thin capsule and pseudopodia).

• Superficial parotidectomy (remove superficial lobe + tumour, preserve facial nerve) - standard for superficial lobe tumours.

• Total conservative parotidectomy (both lobes removed, facial nerve preserved) - indicated for deep lobe involvement or multicompartment disease / tumour spillage.

• Extracapsular dissection - limited excision outside the capsule + small rim of normal tissue.

• Parapharyngeal / deep lesions — cervico-parotid approach; very large / difficult lesions may require transmandibulotomy or transpharyngeal approaches.

What are the indications of Extracapsular dissection in Pleomorphic Adenoma?

2️⃣ Submandibular gland

• Complete excision of the gland with tumour (preserve lingual, hypoglossal, marginal mandibular nerves). Do not perform partial gland excision.

3️⃣ Sublingual gland

• Excision via intraoral approach (gland + tumour).

4️⃣ Minor salivary glands

• Wide local excision with cuff of normal mucosa/periosteum (palatal tumours excised to periosteum) and reconstruction as needed.

🔁 Recurrence & Follow-Up of Pleomorphic Adenoma

• Recurrence rate after superficial parotidectomy ≈ 2–5%, often occurring ~10 years after primary surgery.

• Recurrent tumours are often multicentric and carry a higher risk of malignant transformation (≈3–6%).

• Management of recurrence: Total parotidectomy with facial nerve preservation when possible; consider post-op radiotherapy in selected recurrent/incompletely resectable cases.

• Submandibular recurrence → treat with selective neck dissection (levels I–III) if indicated.

What are the causes of recurrence of Pleomorphic Adenoma?

What is the Imaging for recurrence for Pleomorphic Adenoma?

🩺 Prognosis of Pleomorphic Adenoma

• Excellent if completely excised with clear margins and intact capsule.

• Long-term follow-up required due to late recurrences and small risk of malignant transformation.