Cytohistological Concordance of Papillary Carcinoma of Thyroid and Its Variants

BACKGROUND Papillary thyroid carcinoma is the most common malignancy of the thyroid gland. Fine Needle Aspiration Cytology (FNAC) is a rapid, safe and economic procedure, and has a sensitivity approaching of 93.5 % and specificity close to 90 % for diagnosing papillary thyroid carcinomas. This study aims at correlating the cytological and histological diagnosis to arrive at the rate of concordance and discordance, identify variants of papillary thyroid carcinoma (PTC) on cytology and discuss the cytological mimics of PTC. METHODS Data from cases was collected over a period of three years (2015 - 2018). A descriptive study was done. Cases from Osmania General Hospital representing histologically proven cases of papillary carcinoma thyroid along with their corresponding cytological findings were analysed. Cytosmears were obtained from fine needle aspiration of thyroid lesions using a 26-gauge needle, stained with haematoxylin and eosin (H&E). Thyroidectomy specimens were fixed in 10 % buffered formalin, grossed and paraffin embedded. After processing, sections obtained by microtomy were stained with H & E for histopathologic evaluation. RESULTS The institute received a total of 258 thyroid specimens for histopathology and 686 cases for thyroid FNAC over a period of three years. This study includes 70 cases which had both cytology and histopathology correlation at our institution. 65 cases were diagnosed as PTC on histopathology and correct diagnosis was made on cytology with 73.8 % concordance (48 / 65 cases) and discordance was seen in 26.1 % (17 / 65 cases). 5 cases were misdiagnosed on cytology as PTC, and on histopathological examination were diagnosed as non-PTC. CONCLUSIONS Fine needle aspiration shows variable accuracy for PTC, ranging from 65 % to 90 %. The architectural arrangement of cells in papillary fragments and presence of nuclear features in majority of cells is diagnostic of the conventional variant of PTC. The other variants however, pose a diagnostic dilemma on account of their architectural variation, altered cytomorphology and the scant presence of nuclear features. An increase in the awareness of cytomorphology of variants and also of the mimics of PTC helps improve the diagnostic accuracy on FNAC. KEYWORDS Papillary Thyroid Carcinoma, Variants of PTC, Cytohistopathological Correlation