A 70-Year-Old with a Parotid Swelling and Facial Nerve Weakness

Significance: Facial nerve weakness in the presence of a parotid mass is a red flag for malignancy. Benign parotid tumours (pleomorphic adenoma, Warthin tumour) do not typically cause facial palsy. The presence of palsy indicates:

• Malignant infiltration of the nerve - the most important concern.
• Perineural spread - tumour tracking along the facial nerve.
• Rapid growth with nerve compromise.

Differential diagnosis of a malignant parotid mass with facial palsy:

1. Mucoepidermoid carcinoma - the commonest primary parotid malignancy; high-grade tumours can cause palsy.
2. Adenoid cystic carcinoma - notorious for perineural invasion and late recurrence; facial palsy is a classic feature.
3. Carcinoma ex pleomorphic adenoma - malignant transformation of a long-standing pleomorphic adenoma; suspect if there is a long history of a lump that suddenly grows.
4. Squamous cell carcinoma - primary or metastatic (e.g., from skin).
5. Salivary duct carcinoma - aggressive, often with facial palsy.
6. Acinic cell carcinoma - usually low-grade, less likely to cause palsy.
7. Lymphoma - can involve the parotid; usually no palsy but can occur.
8. Metastatic disease - from skin (SCC, melanoma), especially given the history of BCC - though BCC rarely metastasises.
9. Infective/inflammatory - e.g., deep lobe abscess, tuberculosis, sarcoidosis (less likely with a fixed mass).

Key point: The history of a previous skin cancer raises the possibility of metastatic cutaneous malignancy, although BCC metastasis is rare. A new primary skin SCC or melanoma should be excluded.

This patient needs urgent investigation - the combination of a fixed mass and facial palsy is highly suspicious for malignancy.

Investigations:

1. Imaging:

   • MRI with contrast of the parotid and neck - the investigation of choice. Defines tumour extent, deep lobe involvement, perineural spread (along the facial nerve to the stylomastoid foramen), and cervical lymphadenopathy.
   • CT if MRI is contraindicated; useful for bone erosion.
   • PET-CT - for staging if malignancy is confirmed, to detect distant metastases and other primaries.

2. Tissue diagnosis:

   • Ultrasound-guided core needle biopsy - preferred for suspected malignancy, as it provides architectural information and allows grading (important for mucoepidermoid carcinoma and adenoid cystic carcinoma).
   • FNA - useful for initial triage but has limitations: it cannot reliably distinguish benign from malignant in all cases, and grading is difficult. In a patient with facial palsy, a non-diagnostic FNA should not be reassuring.

3. Blood tests - full blood count, liver function, renal function; consider tumour markers if lymphoma is suspected.

4. Exclude a skin primary - full skin examination, particularly of the head and neck, and review of the previous BCC histology.

5. Baseline facial nerve assessment - document House-Brackmann grade; consider facial nerve function testing (electroneuronography) if relevant.

Role of FNA vs core biopsy:

• FNA is minimally invasive, good for confirming malignancy and distinguishing lymphoma (flow cytometry) from carcinoma, but has a significant non-diagnostic rate and limited ability to grade tumours.
• Core biopsy provides more tissue, allows histological grading and architectural assessment, and is preferred when malignancy is suspected and the result will change management (e.g., deciding between surgery and chemoradiotherapy).
• Open biopsy is avoided in parotid tumours due to the risk of tumour seeding and facial nerve injury.

Practical plan: MRI + US-guided core biopsy, with MDT discussion once histology is available.

Surgical management of high-grade mucoepidermoid carcinoma of the parotid:

1. Parotidectomy - the extent depends on tumour location and grade:

   • Superficial parotidectomy - adequate for a superficial lobe tumour with clear margins.
   • Total parotidectomy - indicated for deep lobe involvement, high-grade tumours, or positive margins. Given the high-grade histology, a total parotidectomy with facial nerve preservation is often preferred, even for superficial tumours, to reduce recurrence risk.
   • Radical parotidectomy - if the facial nerve is involved, with nerve sacrifice and reconstruction.

2. Facial nerve management - the key decision:

   • Preserve the nerve if it is macroscopically uninvolved, even with preoperative weakness (weakness may be due to tumour compression rather than invasion).
   • Sacrifice the nerve if there is macroscopic invasion; reconstruct with a great auricular nerve graft or sural nerve graft, or consider facial reanimation (e.g., temporalis transfer, free gracilis transfer) if the proximal stump is unavailable.
   • Frozen section of the nerve margin intraoperatively guides this decision.

3. Neck dissection - selective neck dissection (levels I-III) is recommended for high-grade tumours, even with a clinically N0 neck, due to the risk of occult nodal metastasis. The MRI showed no nodes, but high-grade histology warrants it.

4. Adjuvant radiotherapy - indicated for:

   • High-grade histology.
   • Positive or close margins.
   • Perineural invasion.
   • Nodal metastasis or extranodal extension.
   • Recurrent disease.

5. Reconstruction - consider volume restoration with a free fat graft or local flap to avoid contour deformity; facial nerve reconstruction if sacrificed.

Key decisions summarised:

• Extent of parotidectomy (superficial vs total).
• Facial nerve preservation vs sacrifice and reconstruction.
• Elective neck dissection.
• Adjuvant radiotherapy.

Prognosis: High-grade mucoepidermoid carcinoma has a poorer prognosis than low-grade; 5-year survival is roughly 50-70% for high-grade disease. Close follow-up with imaging is essential.