Background/purpose: The cytologic features of medullary thyroid carcinoma (MTC) have been described and documented in the literature. Most of the studies were related to the Papanicolaou stain or the May-Grnwald-Giemsa stain. The aim of the present study was to analyze detailed cytologic characteristics of MTC diagnosed by fine-needle aspiration cytology (FNAC) stained with a quick method, Rius stain.
Methods: We collected the FNAC slides of 38 cases with MTC that were proven by surgical pathology. The cytologic findings were reviewed under a light microscope. The median age at diagnosis was 46.5 years, ranging from 13 to 83 years; 20 were women and 18 were men. Among them, seven cases were familial forms and the others were sporadic.
Results: The majority of these cases showed moderate to abundant cellularity. Small round cells, spindle-shaped cells and large oval to polygonal cells formed the usual components. Twenty-seven cases were categorized as pleomorphic cell type and 11 cases as monomorphic type. Except in one case, cohesive and clustered small round cells predominated in all cases, alone or coupled with cohesive spindle cells and/or scattered large oval to polygonal cells. The diagnosis of mixed medullary-follicular thyroid carcinoma was made in the case composed solely of grouped polygonal cells. Cytoplasmic granularities were noted in 14 cases and vacuolations were seen in eight. Binucleated and multinucleated cells were not uncommon, while intranuclear cytoplasmic inclusions were less frequent. The diagnostic sensitivity for MTC by FNAC was 89%.
Conclusion: The distinctive cytopathologic characteristics of MTC by Rius stain allowed us to make the diagnosis in aspiration biopsies accurately and quickly.