This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: ENT
[{'content': 'What is the indication for radical mastoidectomy in an middle aged female? \nSelect and explain. \nA. ASOM, B. CSOM, C. Cholesteatoma invading eustachian tube, D. Acute mastoiditis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Indications for radical mastoidectomy: When all cholesteatoma cannot be safely removed, e.g., that invading eustachian tube, round window niche, perilabyrinthine or hypotympanic cells. If previous attempts to eradicate chronic inflammatory disease or cholesteatoma have failed. As an approach to petrous apex Removal of glomus tumor Carcinoma middle ear', 'role': 'assistant'}]