To determine the efficacy of bilateral inferior petrosal sinus sampling in differentiating Cushing disease from ectopic Cushing syndrome.

Management of endogenous Cushing syndrome is based on its aetiology. Increased Adrenocorticotropic Hormone (ACTH) levels are the most common cause of this disorder and, therefore, it is critical to determine the source of ACTH before further management. Dynamic post contrast MRI is currently the most common investigation implied to diagnose pituitary adenoma; however, it comes with the drawback of low specificity and high false positive results. Inferior petrosal sinus sampling (IPSS) is an established invasive procedure performed to differentiate central versus peripheral source of ACTH which, in turn, results in hypercortesolaemia. This is a series of 14 patients who underwent IPSS at the Department of Radiology, Aga Khan University Hospital, Karachi, from January 2006 to December 2018. The case series emphasises the role of IPSS in the management of ACTH-dependent Cushing syndrome and combined efficacy of Dynamic post-contrast MRI and the procedure under focus.