Between 10% and 20% of patients with hypercortisolism (Cushing Syndrome) have ectopic production of the hormone ACTH. Meaning, the hormone is not being released from the normal site, the pituitary gland. In many cases the ectopic ACTH is being produced by a tumor of the lung, thymus, or pancreas. However, in approximately 50% of these patients the source of the ACTH cannot be found even with the use of extensive imaging studies such as CT scans, MRIs, and nuclear scans (111-indium pentetreotide). The ability of these tests to locate the source of the hormone production is dependent on the changes of anatomy and / or the dose and adequate uptake of the radioactive agent. The inability to detect the source of ectopic ACTH production often results in unnecessary pituitary surgery or irradiation.