Mastoiditis Masquerade.

We report a case of primary temporal bone diffuse B-cell non-Hodgkin lymphoma, which is a rare entity. A 71-year-old male with a history of dementia and hemicraniectomy presented due to 1 month of a pronounced left ulcerative mastoid lesion. Strikingly, there were no cranial nerve deficits which was unexpected due to the degree of the lesion. Initially, infectious mastoiditis was suspected based on physical examination alone. Due to the patient being a poor historian, it was difficult to determine whether this was an acute or chronic issue. Temporal bone squamous cell carcinoma, infectious mastoiditis, and actinomycosis were on the differential, but biopsies revealed non-Hodgkin lymphoma.