Intralabyrinthine Presentation of CNS Lymphoma with Progressive Cerebellopontine Angle Extension

Primary central nervous system lymphoma (PCNSL) rarely involves the cerebellopontine angle (CPA), and intralabyrinthine presentation is unprecedented. We present a 59-year-old man with sudden right-sided hearing loss post-upper respiratory tract infection. MRI showed T2 signal loss in the right vestibule and semicircular canals, suggestive of labyrinthitis ossificans. Symptoms evolved rapidly with facial palsy, ataxia, and gustatory disturbance. Repeat MRI revealed progression to a large CPA mass. Translabyrinthine resection was halted after intraoperative frozen section raised suspicion of lymphoma; final histology confirmed diffuse large B-cell lymphoma. PET-CT showed cauda equina involvement without systemic disease. The patient commenced MATRix chemotherapy with curative intent. Our case highlights the importance of recognizing clinical and radiological red flags when assessing inner ear/CPA pathology. A broad differential should be maintained, and lymphoma considered even in rare locations. Advanced imaging techniques may aid evaluation, but ultimately, biopsy was key to diagnosis and avoiding unnecessary surgery.