What test is used to localize the involved gland in primary hyperparathyroidism?

• A. Ultrasound of the neck
• B. Sestamibi scan
• C. CT scan of the neck
• D. MRI of the neck

Answer: (B)

Localization of the gland driving excess parathyroid hormone is essential to plan a targeted operation. A sestamibi scan uses technetium-99m sestamibi, a radiotracer that is taken up by hyperfunctioning parathyroid tissue and retained longer than thyroid tissue. This functional imaging allows precise localization of the involved gland, including glands that are ectopic in the mediastinum or behind the thyroid. It is more reliable for identifying the culprit gland preoperatively than anatomy-only imaging. Ultrasound can help, but its usefulness is limited by operator dependence and difficulty with ectopic or multigland disease. CT and MRI primarily provide anatomy and are less sensitive for locating hyperfunctioning parathyroid tissue.