In a patient, there are elevated plasma coisol levels. Dexamethasone fails to suppress coisol secretion. What is the next step in management?

This is a patient of Cushing syndrome. Next step is to know ACTH dependent or not.Elevated or normal ACTH levels provide evidence for an ACTH-producing pituitary tumour (85%) or ectopic ACTH production. Therefore, in patients with elevated ACTH, MRI of the pituitary gland must be performed. If MRI is negative, CT scan of the chest and abdomen is warranted to detect an ectopic ACTH-producing tumour.Ref: Bailey and Love 27e pg: 842