If you ask a Cushie, they will tell you that radiologists have an awfully difficult time finding tumors on MRIs of the pituitary. In their defense, these pituitary tumors are very small, often 3-8 millimeters, or a quarter to a half of an inch. These tumors sometimes fall between the 3 mm 'slices' an imaging machine makes, and the patient ends up with images with the 'slices' touching the front and back bumpers of the pituitary tumor but never see the tumor. Many Cushing's patients have MRIs that radiologists read as clear of tumors. Uneducated primary care doctors and endocrinologists thus rule out Cushing's, thus extending the time that the patient wanders around undiagnosed, unhelped, and unwell.
Patients should seek out second opinions from a well-vetted neurosurgeon specializing in pituitary tumors. These doctors understand that tumor detection is more nuanced, and as such, they can usually locate these tumors by examining the structures surrounding the pituitary gland for compression, indentions, or asymmetry. In addition, these doctors are in the unique position to read the MRI before surgery and compare it to what is seen/ found during surgery, thus honing their MRI reading skills. A radiologist has no such environment to do so.