Question: Why do you need to be awake for the IPSS procedure? 

Answer: Inferior petrosal sinus sampling (IPSS) for ACTH is a procedure that is needed in patients with an ACTH secreting tumor causing Cushing syndrome and a normal pituitary MRI. This test samples blood from the venous drainage of the pituitary: small catheters are inserted in the groin and carefully threaded up to the veins near the pituitary called the inferior petrosal sinuses. Blood is taken from these veins for measurement of ACTH before and after the administration of CRH (a hormone that stimulates ACTH from pituitary tumors). The majority of ACTH secreting tumors that cause the adrenal glands to secrete excessive cortisol causing Cushing syndrome are in the pituitary (where ACTH is normally made); however, 10% of ACTH secreting tumors are not in the pituitary (lung, pancreas, etc). IPSS provides confirmation of the presence or absence of a pituitary tumor and may occasionally provide useful information about the location of the tumor within the pituitary gland. These tumors are often very small. Consequently, the neurosurgeon needs all the help he can get and he needs to be confident that there is a tumor in the pituitary before proceeding with surgery.

IPSS should be performed in centers with extensive experience in the proper and safe execution of this procedure. Ideally, patients should be referred to centers where 10 or more procedures are performed annually. The patients should be well informed about the risks of IPSS. Like any invasive procedure, bleeding and possible infection are very rare concerns. Since patients with Cushing are at a very high risk for blood clots, anticoagulation with heparin should always be used during the test. Sedation is always provided to the patients; however, some of the sedatives have a direct effect on ACTH secretion and too much of some sedative drugs could lower the ACTH and theoretically cause confusing results. In addition, the radiologist performing the procedure may wish to talk with the patient during the procedure to be sure they are not having any neurologic symptoms (eg, numbness, speech problems) since very rarely, small strokes have occurred during the procedure. Recognizing these symptoms will alert the radiologist to stop the procedure or change the approach.

Our center performs approximately 15-20 IPSS procedures every year. We always provide as much sedation as needed to keep the patient comfortable. On some occasions (particularly children) we will employ general anesthesia or conscious sedation. Every patient is treated differently depending on the clinical situation and their level of anxiety. Fortunately, IPSS almost always produces unequivocal results that are easy to interpret and thereby gives the endocrinologist and the surgeon a definitive answer to the source of the Cushing syndrome.

By Dr. James Findling, Medical College of Wisconsin, Milwaukee, WI Summer, 2015