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: Unknown
Which of the following statements about Cushing’s disease is true? 
Select and explain. 
A. Serum adrenocorticotropin (ACTH) levels usually are low, B. Pituitary microadenoma usually is present, C. There is a high incidence of nonendocrine tumors, D. Nonsuppression of cortisol production by the high-dose dexamethasone suppression test is a characteristic finding
B: Pituitary microadenoma usually is present
Answer: B: Pituitary microadenoma usually is present 
Explanation: Cushing’s syndrome is due to increased adrenal cortisol production, regardless of etiology.
Cushing’s disease usually is caused by a pituitary microadenoma producing high adrenocorticotropin (ACTH) levels.
In most patients, cortisol levels would be suppressed as a result of the high-dose dexamethasone suppression test.
Transsphenoidal microsurgical removal of the microadenoma is the treatment of choice in most centers.