Cushing’s syndrome is a result of hypercortisolism, which can be due to excessive corticotropin (ACTH) secretion from a pituitary or nonpituitary ACTH-secreting tumor, which drives adrenal cortisol production (ACTH-dependent), or by autonomous adrenal secretion of excessive amounts of cortisol, which is not stimulated by ACTH (ACTH-independent). Identifying the source of ACTH in ACTH dependent Cushing’s is the key to its management. Although Magnetic Resonance Imaging (MRI) is the next investigation of choice, it has lower sensitivity and specificity, and microadenomas that secrete ACTH may be too small to be detected with MRI[. Inferior petrosal sinus sampling (IPSS) is the most reliable method in the confirmation of a central cause of Cushing’s syndrome.