This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
[{'content': 'Commonest extracranial complication of CSOM \nSelect and explain. \nA. Petrositis, B. Labyrinthitis, C. Subperiosteal abscess, D. Facial nerve paralysis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pus may break through mastoid coex leading to subperiosteal abscess which may even burst on surface leading to a discharging fistula It occurs as a sequence of mastoiditis which is a most common complication Ref: Dhingra 7e pg 84.', 'role': 'assistant'}]