This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
[{'content': "Nelson's syndrome is most likely seen after - \nSelect and explain. \nA. Hypophysectomy, B. Adrenalectomy, C. Thyroidectomy, D. Orchidectomy", 'role': 'user'}, {'content': "Answer: B \nExplanation: Adrenalectomy performed by an expe surgeon effectively cures ACTH-dependent Cushing's syndrome, but in patients with pituitary-dependent Cushing's syndrome this can result in Nelson's syndrome. In Nelson's syndrome, the loss of negative feedback from endogenous coisol results in growth of the pituitary tumour, often leading to an invasive pituitary macroadenoma (which causes local mass effects) and very high ACTH levels (which cause pigmentation). The risk of Nelson's syndrome is repoed as being reduced by pituitary irradiation in some series, but not all . Ref - Davidson's medicine 23e p669", 'role': 'assistant'}]