Fine Needle Aspiration Cytology of Mixed Tall and Columnar Cell Papillary Carcinoma of the Thyroid

Abstract

We report the first case of a composite tumor (tall cell and columnar cell variants) of papillary thyroid carcinoma (PTC) diagnosed by fine needle aspiration. It is important to differentiate these uncommon aggressive variants from the usual indolent papillary carcinomas. Fine needle aspiration cytology was obtained from a rare composite tumor of tall cell and columnar cell variants of papillary thyroid carcinoma. The smears showed a cellular aspirate with scattered single tumor cells and several tissue fragments arranged in a papillary pattern. The tumor cells had abundant nuclear grooves and intranuclear pseudoinclusions. Several of the fragments showed columnar cells with nuclear pseudostratification, and a few clusters displayed tall columnar cells with basal nuclei and abundant cytoplasm. A rare cluster exhibited composite features of tall cell and columnar cell variants. Columnar cell and tall cell variants of PTC manifest aggressive clinical behavior. The differential diagnosis of columnar cell variant includes medullary carcinoma of thyroid and metastatic adenocarcinoma. Immunohistochemical stains for calcitonin and thyroglobulin play an important role in difficult cases. The tall cell variant needs to be differentiated from Hürthle cell papillary neoplasm of thyroid, which displays prominent nucleoli and lacks the characteristic nuclear features of PTC. The preoperative diagnosis of these aggressive variants' is important in planning the most appropriate type of treatment.