In a 30‑60‑year‑old adult with a painless pre‑auricular mass, what is the presentation, diagnostic work‑up, and management of pleomorphic adenoma of the parotid gland?

Pleomorphic Adenoma of the Parotid Gland

Clinical Presentation

Pleomorphic adenoma presents as a slow-growing, painless, firm mass in the pre-auricular region, typically inferior to the pinna of the ear, most commonly affecting women between 30–60 years of age. 1, 2

• The mass is usually asymptomatic and grows slowly over months to years 1
• Facial nerve function remains intact—any facial weakness should immediately raise suspicion for malignancy rather than benign pleomorphic adenoma 3
• The tumor most commonly arises in the superficial lobe of the parotid gland (approximately 80% of cases) 4
• Pain, rapid growth, facial nerve paralysis, or palpable cervical lymphadenopathy are red flags that suggest malignant transformation or an alternative diagnosis 3

Diagnostic Work-Up

Initial Imaging

MRI with and without intravenous contrast is the preferred imaging modality for suspected pleomorphic adenoma, as it provides superior soft-tissue delineation of tumor extent, relationship to the facial nerve, and potential deep-lobe involvement. 3

• Ultrasound can serve as a first-line screening tool to differentiate solid from cystic lesions and guide fine-needle aspiration, but MRI is superior for surgical planning 5
• CT with IV contrast is an alternative when MRI is contraindicated, though it provides inferior soft-tissue detail 3, 5

Tissue Diagnosis

Fine-needle aspiration biopsy (FNAB) using the Milan System for Reporting Salivary Gland Cytopathology should be performed preoperatively to confirm the diagnosis and assess risk of malignancy. 3

• FNAB demonstrates 98.5% sensitivity and 99% specificity for detecting malignant parotid tumors 3
• Ancillary testing (immunohistochemistry or molecular studies) on FNAB specimens may support the diagnosis 3
• The cytopathology report should include a risk-of-malignancy (ROM) classification to guide surgical planning 3

Mandatory Clinical Assessment

Comprehensive facial nerve testing of all five branches (temporal, zygomatic, buccal, marginal mandibular, cervical) must be documented before any intervention. 3

• Even subtle facial weakness indicates potential nerve involvement and suggests malignancy rather than benign pleomorphic adenoma 3
• Assess for cervical lymphadenopathy, which markedly increases suspicion for malignancy 3, 5
• Evaluate for trismus or cranial nerve numbness, which suggest deep invasion or perineural spread 3

Surgical Management

Extent of Resection

For benign pleomorphic adenoma in the superficial lobe, partial superficial parotidectomy with complete capsule excision and facial nerve preservation is the appropriate surgical approach. 3, 4

• Partial superficial parotidectomy achieves excellent disease control with fewer complications and low recurrence rates compared to total parotidectomy 3, 4
• The entire tumor capsule must be removed to prevent recurrence, as capsule infiltration is associated with tumor recurrence 4
• For deep-lobe tumors, total parotidectomy is typically required 4

Facial Nerve Management

The facial nerve should be identified, dissected, and preserved in all cases of benign pleomorphic adenoma, as preoperative facial nerve function is intact and a dissection plane can be created between tumor and nerve. 3

• The main trunk of the facial nerve emerges from the stylomastoid foramen and divides into temporofacial and cervicofacial divisions 3
• Facial nerve sacrifice is never indicated for benign pleomorphic adenoma 3
• Intraoperative frozen section may guide extent of resection but should not be the sole basis for major surgical decisions 3

Surgical Margins

Complete excision with adequate free margins is essential, though narrow margins (≤5mm) show excellent disease control for benign tumors without adverse features. 3

• Margin status significantly affects outcomes, though this is more critical for malignant tumors 3, 6

Key Clinical Pitfalls

Do not delay imaging or tissue diagnosis by treating a parotid mass empirically with antibiotics, as this practice delays cancer detection if malignancy is present. 3

• Pleomorphic adenoma has a risk of malignant transformation (carcinoma ex-pleomorphic adenoma), particularly in longstanding tumors, with a five-year recurrence rate of 75% once malignant transformation occurs 2
• Longstanding tumors (>30 years) can reach enormous sizes (up to 28 cm and 4 kg reported) but still may be benign without malignant transformation 7
• Do not assume a cystic-appearing mass is benign—malignant tumors can present with cystic components 3

Postoperative Considerations

• Transitory facial nerve paralysis occurs more frequently after total parotidectomy compared to partial superficial parotidectomy 4
• Recurrence rates are low (<2%) with appropriate surgical technique that includes complete capsule removal 4
• Outpatient surgery is safe and appropriate for benign parotid tumors 3