Biopsy of the facial nerve in slow-onset facial palsy.

Introduction: Primary squamous cell carcinoma of the parotid gland typically presents as a palpable, often painless mass. Peripheral facial palsy as the only sign of malignant neoplasia is rare. In these cases, the diagnosis is regularly confirmed by radiological imaging followed by surgical exploration and biopsy. However, if there is no detection of malignant lesions and no evidence of a tumor, the reluctance to take a biopsy of an unremarkable nerve can lead to misdiagnoses.

Case report: A 40-year-old female patient without medical history presented to our clinic with a complete right-sided peripheral facial palsy that had slowly progressed for 2.5 years. All other otorhinolaryngological examination findings were within normal limits. Magnetic resonance imaging examination of the head and neck and 18-fluorodeoxyglucose positron emission tomography showed unremarkable results. We proceeded with surgical exploration, which revealed no evidence of a tumor and an externally completely unremarkable facial nerve. A biopsy from the main trunk area of the nerve revealed an infiltration by a squamous cell carcinoma. Total parotidectomy with resection and reconstruction of the facial nerve and neck dissection was performed. Considering the absence of a primary tumor and other tumor formations the diagnosis of a completely regressive primary squamous cell carcinoma of the parotid gland was confirmed.

Conclusion: In conclusion, in the case of slow-onset peripheral facial palsy that persists without signs of recovery, a gadolinium-enhanced MRI should be performed. If imaging is unremarkable and there is no primary tumor detection along the course of the facial nerve, a surgical exploration with biopsy of the facial nerve is necessary.