This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroid and adrenal glands, Subject name: Surgery
Commonest cause of Cushing syndrome is: 
Select and explain. 
A. Adrenal adenoma, B. Carcinoma, C. Hyperplasia, D. Atrophy
C: Hyperplasia
Answer: C: Hyperplasia 
Explanation: MC cause of Cushing's syndrome is iatrogenic exogenous administration of steroids MC endogenous cause of Cushing's syndrome is bilateral adrenal hyperplasia secondary to hypersecretion of ACTH from pituitary or from an ectopic non-pituitary source. Cause of Cushing's Syndrome Endogenous Exogenous ADRENAL HYPERPLASIA Pituitary ACTH overproduction: Microadenoma>Marcoadenoma Ectopic ACTH overproduction: Small cell carcinoma lung Thymus carcinoid Carcinoma pancreas Bronchial adenoma Iatrogenic exogenous administration of steroids (MC cause) ADRENAL NEOPLASIA Adenoma Cacrinoma