**5. Conclusions**

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 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:

a.biochemical factors


b.biological factors


Uptake of 99mТс-sestamibi and 99mТс-tetrofosmin in the cells of the parathyroid adenomas depends on the activity of the P glycoprotein coded by MDR gene, which is functioning as an ATP dependent efflux pump, protecting against accumulation of lipophilic cationic radiopharmaceuticals, including 99mТс-tetrofosmin [60]. The expression of P glycoprotein in the parathyroid adenomas appears to be important factor determining radiopharmaceutical uptake. In one study 71% (10 out of 14) of adenomas with high P glycoprotein membrane activity have shown negative scans, 70% (45 out of 64) with negative P glycoprotein expression (р = 0.006) have shown positive scans [61].
