Imaging of auriculotemporal nerve perineural spread

IMPORTANCE: Adenoid cystic carcinomas (ACCs) are relatively rare tumours, notorious for wide local infiltration and perineural spread. Perineural extension commonly occurs along branches of the trigeminal and facial nerves, and its presence represents a poor prognostic factor with implications for treatment approach. OBSERVATIONS: We report the case of a 61-year-old female presenting with worsening left facial numbness and weakness. On magnetic resonance imaging, the patient was found to have perineural spread of a left parotid tumour along the auriculotemporal nerve. There was involvement of the V2 and V3 branches of the trigeminal nerve. An ultrasound-guided biopsy of the mass demonstrated ACC. CONCLUSIONS AND RELEVANCE: The auriculotemporal nerve may serve as a route for tumour spread, particularly in the setting of head and neck malignancy. Moreover, this particular suspicion should be raised when patients with known malignancy experience concomitant trigeminal (V) and facial (VII) nerve dysfunctions.