Preoperative testing to find a parathyroid tumor is now considered 'standard of care'.  In other words, virtually all patients should have a "localizing study" prior to having parathyroid surgery. Of course, as discussed in several other areas of this large parathyroid web site is the Sestamibi Scan... which is undoubtedly the preferred parathyroid test.

If a Minimally Invasive Parathyroid Surgery (which is performed under local anesthesia in an outpatient setting) is planned, then often the only preoperative test necessary is a Sestamibi scan the morning of the operation. The following tests are performed very infrequently and under very specific and unique circumstances. They are discussed here briefly only for education purposes.
parathyroid adenoma ultrasound ultrasound locate surgery surgery operate operation operation parathyroid cancer tumor hormone

CAT scanning has always been a poor localizing test for enlarged parathyroids. There are currently very rare indications for the use of CAT scans in this setting and this test should never be performed routinely. The MRI scan is more sensitive and specific than the CAT scan when looking for enlarged parathyroid glands. Since many endocrine tumors enhance on a T-2 weighted MRI scan this is the preferred anatomic localizing test over CAT scanning. The photo shows a T-2 weighted MRI of a parathyroid adenoma in the lower left neck within the tracheo-esophageal groove. The indications for MRI scanning, however, are still extremely uncommon. Most patients do not require any localization...and if localization is required, the Sestamibi scan is the preferred method. MRI scans should probably be reserved for patients with recurrent or persistent disease who have already had one unsuccessful operation.
Cat scan MRI CT ultrasound parathyroid parathyroid cancer operate surgery surgery

Ultrasound

Ultrasound is an inexpensive and non-invasive way to look for parathyroid adenomas. Although it is less sensitive and specific than the MRI scan, it is still used frequently because it is readily available, fast and low in cost. Again, most patients do not need any of the localizing studies discussed on this page (CAT scanning, MRI, or ultrasound). Prior to a standard exploration, no localizing test is needed. Prior to Minimally Invasive Parathyroidectomy, a Sestamibi scan is mandatory. Since about 1995, the need for using any scanning method other than sestamibi is extremely infrequent. Ultrasound fails to find a parathyroid adenoma half of the time, therefore, it may be cheap, easy, painless, and safe, but its not very good either. Even when it does "suggest" the location of an adenoma, it is wrong 20 percent of the time, therefore, it is not accurate enough to allow a surgeon to take out this one gland without examining all three other parathyroids. Therefore, ultrasound will not allow a small operation or the use of local anesthesia.

More on Sestamibi Scanning

Technical Details on How to Perform High Resolution Sestamibi Scans [intended for physicians]

Parathyroid Basics