A sestamibi scan of the parathyroi gland is a nuclear medicine procedure which is performed to identify hyperparathyroidism (or parathyroid adenoma). Sestamibi is a nuclear radiopharmaceutical (methoxy-isobutyl-isonitrile) which is bound to the radioactive isotope Tc99m. Tc99m-sestamibi is taken up by both the thyroid gland and the parathyroid gland, but can also be taken up by enlarged thymus or lymph nodes within the neck, and is also used in nuclear myocardial perfusion imaging and in detection of very early stage breast cancer.