To present pathological processes of the TG with histological detection of granulomas, analysis of morphological forms of granulomas, and their diagnostic significance. This paper is based on literature review and insight into the archival materials of the Institute of Pathology and Forensic Medicine of the Military Medical Academy.The presence of granulomas in the thyroid gland (TG) includes specific pathological processes such as subacute thyroiditis (SAT) and palpation thyroiditis (PT). The clinical manifestations of the granulomas may be accompanied by symmetrical or asymmetrical enlargement and palpatory pain in the gland, which requires further clinical examination. Granulomas in the TG can be associated with various benign and malignant processes. There are two large groups of granulomas: foreign-body giant cell granulomas (FBG) and immune granulomas (IGR). FBG are histiocytic reactions to chemically inert, exogenous or endogenous materials. Etiologically, IGRs arise in the framework of infectious, autoimmune, toxic, drug-induced or pathological processes of unknown etiology. According to the presence of necrosis IGRs can be further divided as necrotizing or non-necrotizing type. TG granulomas of the infectious, autoimmune or inflammatory nature of the unknown etiology are extremely rare. 1. Granulomas in specific pathological processes of the TG Subacute (de Quervain’s) thyroiditis or granulomatous thyroiditis is an inflammatory process that is clinically presented as enlarged and painful TG. In most cases, the result is a complete recovery of the TG function. Permanent hypothyroidism is found in about 5% of patients. SAT is usually preceded by upper respiratory tract infection. The disease is etiologically related to viral infections, genetic predisposition and the use of immuno therapy. Macroscopically, TG is usually symmetrically enlarged, but there are also localized forms with nodular morphology, which imitate neoplastic lesions. The microscopic characteristic is the presence of multifocal and diffusely distributed folliculocentric granulomas. They are found in different phases and consist of epitheloid histiocytes, lymphocytes, plasma cells, neutrophils, and multinuclear giant cells (MGC). At the center of the granuloma, the colloid is reduced or absent. In later phases, fibrosis can develop perifollicularly. In terms of differential diagnosis (DDG), it is important to differentiate SAT from other granulomatous inflammations. Palpation thyroiditis (Multifocal granulomatous folliculitis) is the most common pathological process in TG with microscopic detection of granulomas. It is an incidental microscopic finding involving individual or minor follicular groups. Changes arise as a result of mechanical microtrauma after the palpation of the TG. Microscopic changes are characterized by damage to the follicles with interfollicular APSTRAKTI 73 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. accumulation mainly of histiocytes in the presence of lymphocytes, plasma cells and MGCs. In the DDG of PT, the following conditions must be considered: SAT, primary and secondary microscopic foci of papillary microcarcinoma, C-cell hyperplasia, and focal forms of Langerhans histiocytosis. 2. Foreign-body giant cell granuloma is frequent incidental microscopic finding in TG. It arises as a reaction to the accumulation of endogenous substances in the areas of spontaneous or degenerations induces by fine-needle aspiration biopsy (FNAB). The most common forms of FBGs on endogenous material are cholesterol granulomas. These FBGs are composed of MGCs, foamy histiocytes, and hemosiderophages arranged around crystal deposits. Depending on how old the lesion is, there may be a focal necrosis, a different degree of fibrosis, extracellular deposits of hemosiderin, and other inflammatory cells. The presence of FBGs and histiocytic aggregates is not only important in the preoperative cytological diagnostics, but also in the post-operative pathohistological analysis of TG nodules. Large nuclei of histiocytes with hypochromasia, nuclear membrane irregularities and the presence of MGC can imitate the cytological features of papillary thyroid carcinoma (PTC). Exogenous biomaterials are rarely cause of FBGs in TG. After thyroidectomy, in cases of diagnosed TG malignancies, the presence of suture FBGs in thyroid bed imitates recurrence or the rest of malignancy and is the cause of repeated surgeries. 3. Necrotizing granulomas (NGR) in TG Granulomas with necrosis may be of infectious and noninfectious etiology. Tuberculosis is the most common cause of NGR in TG. Tuberculosis in TG can be presented as a solitary nodal lesion, diffuse microlesions, nodular goiter, and rarely as an abscess or a chronic skin sinus. As a infectious cause of NGR in TG, sporadically reported cases have been caused by histoplasmosis, coccidioidomycosis and nocardiosis. Rare non-infectious NGR in TG or in the TG bed, of autoimmune etiologies, have been described as part of Wegener’s granulomatosis and rheumatoid arthritis. Post-operative necrotizing granulomas also represent NGR of non-infectious cause. Microscopically, there is a morphology that matches post biopsy granulomas in other organs (prostate, urinary bladder). 4. Non-necrotizing granulomas (NNGR) in TG Sarcoidosis is a multi-systemic chronic granulomatous inflammation of unknown etiology. Thyroid is rarely affected by sarcoidosis. Macroscopically, the gland is diffusely or nodularly enlarged or reduced in volume. Interstitially localized NNGR represent a typical histological presentation. Sarcoidosis of TG should be distinguished from the sarcoid-like stromal reactions of PTC in the gland or regional lymph nodes. In these cases, it is necessary to clinically exclude the systemic disease. 5. Granulomas and histiocytic reactions in neoplastic processes of TG Apart from the described FBGs, PT and sarcoid-like reactions, in epithelial tumors of the TG histiocytic aggregates (not granulomas) may also be seen as secondary changes after FNAB. Interfollicular/ intraluminal presence of MGCs with or without the presence of histiocytes and granuloma-like morphology represents a characteristic finding in PTC. The cytological and histological detection of MGCs is one of the diagnostic criteria for PTC. Their presence in tumors may be due to a reaction to an altered colloid produced by PTC or as a non-specific immune response to due tumor cells. Conclusion: Granulomas in the TG are not rare. Knowing the morphology of granulomas, pathological processes and the circumstances in which they occur is significant in DDG of primary tumors of the TG, their recurrence and metastases in the cervical lymph nodes. The diagnosis of granulomatous inflammation in TG can be based on the histological characteristics of granulomas in correlation with clinical and laboratory findings.

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