A 52-year-old man presents with a painless swelling over the angle of the mandible that has been slowly enlarging over 6 months. On examination, the swelling is firm, non-tender, and located anterior to the sternocleidomastoid muscle. What is the most common benign tumor of the parotid gland?

Explanation

## Most Common Benign Parotid Tumor **Key Point:** Pleomorphic adenoma (mixed tumor) accounts for approximately 60–80% of all parotid gland tumors and is the single most common benign neoplasm of the parotid gland. **High-Yield:** Pleomorphic adenoma is characterized by a slow, painless growth over months to years, firm consistency, and a well-defined capsule. It arises from the salivary gland acini and contains both epithelial and mesenchymal (myxoid, chondroid) components. ### Clinical Features of Pleomorphic Adenoma | Feature | Details | | --- | --- | | **Incidence** | 60–80% of parotid tumors | | **Age of onset** | 40–60 years (can occur earlier) | | **Growth rate** | Slow, over months to years | | **Consistency** | Firm, non-tender | | **Location** | Superficial lobe (80%), deep lobe (20%) | | **Facial nerve involvement** | Rare (indicates malignancy) | | **Malignant potential** | 1–5% risk of transformation over time | **Clinical Pearl:** The classic presentation is a painless, slow-growing swelling in the angle of the mandible anterior to the sternocleidomastoid muscle — exactly as described in this case. The absence of facial nerve paralysis, pain, or skin involvement favors benign disease. **Warning:** Do not confuse pleomorphic adenoma with Warthin's tumor (papillary cystadenoma lymphomatosum), which is the second most common benign tumor (10–15% of parotid tumors) and typically occurs in older males with a smoking history. Oncocytoma and myoepithelioma are much rarer. ### Differential Diagnosis of Parotid Tumors | Tumor | Frequency | Key Features | | --- | --- | --- | | **Pleomorphic adenoma** | 60–80% | Slow growth, mixed epithelial-mesenchymal, low malignant potential | | **Warthin's tumor** | 10–15% | Older males, smokers, cystic, lymphoid stroma | | **Oncocytoma** | 2–3% | Older patients, bilateral in 10%, oncocytes (mitochondria-rich) | | **Myoepithelioma** | <1% | Rare, myoepithelial differentiation | | **Mucoepidermoid carcinoma** | 5–10% (malignant) | Most common malignancy, variable grade | **Mnemonic:** **PAWM** — Pleomorphic adenoma, Adenolymphoma (Warthin), Oncocytoma, Myoepithelioma — in order of frequency among benign tumors.