[PREOPERATIVE DIAGNOSTICS OF THYROID MEDULLARY CARCINOMA WITH EMPHASIS ON CYTOMORPHOLOGICAL FEATURES AND DIFFERENTIAL DIAGNOSIS OF PRIMARY AND SECONDARY THYROID TUMORS].

Medullary thyroid cancer is a rare neuroendocrine neoplasm that arises from the parafollicular C cells that produce calcitonin, a hormone essential for the regulation of calcium metabolism. It accounts for 4%-10% of all thyroid cancers. In most cases (75%-80%), it is sporadic, while in other cases it is part of the multiple endocrine neoplasia (MEN) syndrome. Most often, medullary thyroid carcinoma is presenting as a solitary nodule. At the time of diagnosis, about half of the patients have enlarged cervical lymph nodes, while a small number of patients have distant metastases in the liver, lungs, bones and brain. If the tumor is hormone active, the patient may have systemic symptoms such as diarrhea or flushing. Ultrasonically, medullary carcinoma usually appears as a hypoechogenic node with marked vascularity and uneven contours that can sometimes contain microcalcifications, and in most cases is located in the upper poles of the thyroid. The sample obtained by fine needle aspiration is usually cellular, tumor cells are disseminated or arranged in poorly cohesive groups. They are most often plasmacytoid, but sometimes can also be spindled. The nuclei are eccentric and chromatin shows features of neuroendocrine tumors. Cytoplasms of tumor cells are abundant, triangular or polygonal, amphophilic, finely granulated and unsharply limited. Background is clean and sometimes amyloid can be found. Depending on the cytologic picture, differential diagnostic problems can be well differentiated thyroid tumors, primarily follicular neoplasm, lymphomas, poorly differentiated insular carcinoma, metastatic small cell carcinoma, mesenchymal tumors or melanoma. In case of differential diagnostic difficulties, of great help is to determine calcitonin immunocytochemically or in aspirate or serum. Medullary carcinoma may show low progression and long-time survival, but can also be a rapidly progressive tumor where survival is measured in months. Good prognostic indicators are younger age, female gender, tumor size, tumor localization only in the thyroid gland, and absence of local or distant metastases. In conclusion, medullary thyroid carcinoma is a rare tumor in which we still have to think in diagnosing thyroid nodules, mainly due to adequate preoperative preparation in terms of exclusion of pheochromocytoma in MEN syndrome. Cytologic picture in some cases is typical; however, immunocytochemical evidence of calcitonin is of great help to confirm morphological diagnosis.