A case of adenoid cystic carcinoma in the temporal bone, misdiagnosed as acute idiopathic facial paralysis

Adenoid cystic carcinoma (AdCC) constitutes approximately 1% of head and neck tumors. The external auditory canal is the most prevalent site in the otologic area but AdCC developed in a mastoid is extremely rare and seems to be misdiagnosed as benign inflammatory lesion. Because of its neurotropism, it may involve adjacent nerve early and facial nerve paralysis can develop in the early stage. But its diagnosis, especially in the early stage, is often challenging. Our case report describes a case of a patient with advanced unresectable AdCC in right mastoid with persistent peripheral facial paralysis, which was initially diagnosed as idiopathic Bell’s palsy. Clinicians should be vigilant when treating patients with persistent facial paralysis, especially when imaging studies reveals a lesion around facial nerve in the mastoid, because this may indicate AdCC. This case highlights the diagnostic basis, treatment, and outcomes for this case to improve the understanding of AdCC in the mastoid.