This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cushing Syndrome, Subject name: Medicine
[{'content': 'All of the following are ACTH independent Cushing syndrome except : \nSelect and explain. \nA. Pituitary adenoma, B. Adrenal hyperplasia, C. Adrenocoical carcinoma, D. McCune Albright Syndrome', 'role': 'user'}, {'content': "Answer: A \nExplanation: ACTH dependent Cushing syndrome is caused by : ACTH producing pituitary adenoma Ectopic ACTH Bronchial or pancreatic carcinoid Small cell cancer of lung Medullary carcinoma of thyroids Pheochromocytoma ACTH Independent Cushing syndrome is caused by : Adrenocoical adenoma/ carcinoma Primary pigmented nodular adrenal disease Adrenal hyperplasia McCune Albright Syndrome Petrosal/Peripheral ACTH ratio > 2 indicates the presence of a pituitary adenoma-secreting ACTH. NOTE: Overall the most common cause of Cushing's syndrome is Iatrogenic steroids but if asked regarding ACTH dependent cause then answer should be given as Pituitary adenoma.", 'role': 'assistant'}]