Petrosal Sinus Sampling (IPSS):  It is an interventional neuroradiology procedure used in patients with ACTH-dependent Cushing’s syndrome to distinguish between Cushing’s disease (from a pituitary adenoma) and ectopic Cushing’s (typically from a lung carcinoma). IPSS should only be performed by experienced neuro-radiologists and only after an initial and thorough endocrine evaluation. The procedure is usually performed under general anesthesia and involves injection of corticotropin releasing hormone (CRH) then followed over the next 10 minutes by multiple measures of serum ACTH levels in the right and left inferior petrosal sinuses and in the peripheral blood.  Learn more.