Cushing's disease testing may include a petrosal sinus sampling. This test is not always required to make a Cushing's disease diagnosis, but in many cases, it is the best way to separate pituitary from ectopic causes of Cushing's syndrome.

 

Samples of blood are drawn from the petrosal sinuses -- the veins that drain the pituitary -- by introducing catheters through a vein in the upper thigh or groin region, with local anesthesia and mild sedation. X-rays are used to confirm the correct position of the catheters. Often, CRH, the hormone that causes the pituitary to secrete ACTH, is given during this test to improve diagnostic accuracy. Levels of ACTH in the petrosal sinuses are measured and compared with ACTH levels in a forearm vein. ACTH levels higher in the petrosal sinuses than in the forearm vein indicate the presence of a pituitary adenoma.