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: Surgery
[{'content': 'Source of chronic subdural hematoma is: September 2011 \nSelect and explain. \nA. Aerial, B. Venous, C. Capillaries, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B: Venous Chronic subdural haematomas usually occur in the elderly and are more common in those on anti-coagulant or anti-platelet agents. There is usually but not always a history of minor head injury in the weeks or months prior to presentation. It is thought that small bridging veins tear and cause a small acute subdural haematoma which is clinically silent As the haematoma breaks down it increases in volume, leading to a mass effect on the underlying brain', 'role': 'assistant'}]