The visualization of abnormal parathyroid glands is difficult due to their variations in number and localization. Noninvasive parathyroid imaging studies include 99mTc-sestamibi scintigraphy, ultrasonography, computed tomography scanning, magnetic resonance imaging, and positron emission tomography. There is a general consensus that the most sensitive and specific imaging modality, especially when it is combined with single-photon emission CT is the scintigraphy with 99mTc-sestamibi or 99mTc-tetrofosmin. 99mTc-sestamibi scintigraphy significantly increases the role of preoperative scintigraphy in patients with hyperparathyroidism and allows unilateral surgical approach with minimally invasive parathyroidectomy to be used. Generally, three protocols with the use of two radiopharmaceuticals, 99mTc-sestamibi or 99mTc-tetrofosmin, are most widely applied: single-phase dual-isotope subtraction, dual-phase single-isotope and combination of both. Each one of them has specific advantages and disadvantages. While single parathyroid adenomas are localized with greater precision, hyperfunctioning parathyroid hyperplastic cells represent a real challenge to the imaging modalities. Several factors can influence the radionuclide uptake in pathologically changed parathyroid cells, like the size, the level of their functional activity, the quantity of oxyphilic cells, mitochondria, P glycoprotein and other MDR gene products.
Advantages of the 99mTc-sestamibi single-photon emission computed tomography/computed tomography in occult parathyroid adenoma and concomitant thyroid papillary carcinoma
