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': 'Most difficult site to remove cholesteatoma in sinus tympani is related with - \nSelect and explain. \nA. Anterior facial ridge, B. Posterior facial ridge, C. Epitympanum, D. Hypotymparum', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The sinus tympani (Posterior facial ridge) is the posterior extension of the mesotympanum and lies deep to both the promontory and facial nerve.\nThe medial wall of sinus tympani becomes continuous with the posterior portion of the medial wall of the tympanic cavity. This is the worst region for access because it is above pyramid, posterior to intact stapes and medial to facial nerve.\nA retro facial approach via mastoid is not possible because the posterior semi circular canal blocks the access.', 'role': 'assistant'}]