You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Commonest extracranial complication of CSOM and explain in detail?
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.