For hormone secreting tumors (Cushings, acromegaly, prolactinomas), blood and urine tests in the days or weeks following surgery provide the answer. For non-secreting tumors, pituitary MRI scans are used to determine this. Some centers, such as Massachusetts General Hospital, have a special MRI machine in the operating room, which is used in patients with large tumors, to follow the progress of tumor removal during the operation. Because the surgeon works only from the inside of the tumor, it is sometimes difficult to tell how much tumor remains during the procedure. The intra-operative MRI helps us to see whether there is more to be removed. Tumor in the cavernous sinus can rarely be removed even with the use of the MRI (as noted in Question 4). A postoperative MRI is obtained about six weeks after the surgery. This helps determine whether further therapy is required. If the tumor is a hormone secreting adenoma (prolactinoma, Cushings disease or acromegaly), the endocrinologist will follow your hormone levels postoperatively to determine whether you are cured.