The procedure to collect blood from the petrosal sinus is called Inferior Petrosal Sinus Sampling (IPSS). The technique is very sensitive and can tell the difference between a pituitary tumor and other causes of Cushing syndrome nearly 100% of the time. However, IPSS is very difficult to perform and is only available in a few hospitals. Therefore, researchers are looking for another possible way to diagnose Cushing syndrome that would be less technically difficult and more readily available to patients.