Factors associated with the degree of 99mTc-MIBI accumulation in parathyroid glands neoplasms during planar scintigraphy and SPECT/CT in primary hyperparathyroidism

Background: Primary hyperparathyroidism (PHPT) is the third most common endocrine disease, after diabetes mellitus and thyroid gland disorders. Surgical removal of the hyperfunctioning parathyroid glands is the only radical treatment. Various methods of preoperative imaging and intraoperative navigation are developed. Planar scintigraphy with ^99mTc-MIBI is used for visualization and it is the most frequently performed radionuclide study in PHPT, while it has a relatively low sensitivity and specificity. SPECT/CT can reduce false-negative and false-positive results, and combines the advantages of radionuclide diagnostic methods and computed tomography. However, the factors that prevent the accumulation of ^99mTc-MIBI in patients with PHPT are not clear enough.

Aim: To identify the factors associated with the degree of accumulation (uptake rate) of ^99mTc-MIBI in the parathyroid glands during planar scintigraphy and SPECT/CT.

Materials and methods: The cross-sectional comparative study included 186 patients with PHPT who underwent planar scintigraphy and SPECT/CT for topical diagnosis of parathyroid glands and minimally invasive parathyroidectomy (MIP) followed by histological and immunohistochemical examination of parathyroid glands. The patients were divided into 3 groups depending on the accumulation of ^99mTc-MIBI. The accumulation of ^99mTc-MIBI was assessed by the expert as low-, moderate-, and high-intensity.

Results: The association between the volume of the parathyroid glands on ultrasound and the intensity of the capture of the radiopharmaceutical was revealed, and 80% of low uptake is observed if volume is less than 0,215 cm³ (it corresponds to the linear size of the parathyroid gland ≤5 mm). Next factor that complicate the interpretation of the results of planar scintigraphy and SPECT/CT in patients with PHPT is thyroid diseases. The associations of the level of PTH, calcium in the blood, the localization and cellular composition of the parathyroid glands, the index of proliferative activity (Ki67), the expression of PTH, P-glycoprotein, cyclin D1 in the PTG tissue with the intensity of ^99mTc-MIBI accumulation were not found.

Conclusions: The main factor that positively associates with the degree of ^99mTc-MIBI accumulation with planar scintigraphy and SPECT / CT is the volume of the parathyroid glands according to ultrasound data. Comorbidity of the thyroid gland has tendency to be associated with a negative result of radionuclide diagnostics, thus based on the ultrasound data of the thyroid and parathyroid glands it is possible to choose the second preferable method of imaging (SPECT/CT or contrast enhanced CT).