Introduction: It was reported that 19.8–32.1% of thyroid nodules have signs of one of the different calcification types and that the prevalence of calcification is around 40% in malignant and 20% in benign nodules. The occurrence of calcification in some thyroid lesions could be easily identified and provides useful information regarding tentative diagnoses. A better understanding of the mechanisms of thyroid calcification can be useful both in planning and in the actual treatment of patients. 

Aim: of our work is to study the morphology, structure, and phase composition of pathological calcifications in benign thyroid tumors.

Materials and methods: We studied 48 cases of benign thyroid neoplasms with pathological biomineralization to establish their structural, phase, and elemental composition, as well as morphological features. All samples were examined by histology and histochemistry in order to verify the histological type of thyroid tumors and confirm the presence of calcifications. SEO-SEM Inspect S50-B was used for scanning electron microscopy. Spectra were analyzed in the standard software of the microanalysis system. X-ray diffraction was performed with a diffractometer DRON-7.4 (“Burevestnyk”). Transmission electron microscopy with electron diffraction was performed with TEM125K (SELMI, Ukraine). 

Results: The biomineralization occurred in the connective tissue of nodes capsules, sometimes extended to the thyroid parenchyma, interfollicular space, colloid, follicular epithelium. The calcifications of the capsule and parenchyma were stained brown when the thyroid tissue was stained by the von Koss method. At the same time, colloidal calcifications were not stained.

Conclusions: According to the data of complex researches, it is established that pathological biomineral deposits of benign thyroid neoplasms are represented by nanocrystalline apatite and calcium oxalate. Calcifications of the capsules of the nodes and large mineral deposits of the thyroid parenchyma consist of hydroxyapatite, and calcifications of the correct rectangular shape, located in the colloid, consist of calcium oxalate. Therefore, the obtained data can be further used to diagnose benign and malignant neoplasms of the thyroid gland.