Cytodiagnosis of benign and malignant Hürthle cell lesions of the thyroid by fine-needle aspiration biopsy.

Eighty-two Hürthle cell (HC) lesions of the thyroid with cytologic evaluation by fine-needle aspiration biopsy (FNAB) were reviewed. In 17 cases the FNAB was not diagnostic because the fine-needle aspirates (FNAs) were too scanty in cellularity. Among the remaining 65 lesions, there were 45 HC adenomas (HCAs), six non-neoplastic HC nodules (NHCNs), 10 primary HC carcinomas (HCCs), and four metastatic HCCs. Forty-four HCAs were diagnosed as HC tumor (HCT), and one HCA was wrongly diagnosed as medullary carcinoma. All six NHCNs were wrongly diagnosed as HCT. Of 10 primary HCCs, there were diagnosed as HCT and seven as suspected HCC. Four metastatic HCCs were correctly diagnosed. The FNAs from 38 HCAs and four NHCNs were predominantly composed of large monomorphic HCs with oval nuclei, inconspicuous nucleoli, and abundant, well-defined, granular cytoplasm present singly, in acinar arrangement, and in monolayered sheets of variable sizes. Nuclear pleomorphism and prominent nucleoli were noted in seven HCAs and two NHCNs. Occasional small syncytial tumor cell clusters (STCCs) were noted in six cases, and a few naked tumor cell nuclei (NTCN) were observed in 16 cases. The FNAs from 14 HCCs were hypercellular. In all cases tumor cells were relatively small and showed monomorphic or pleomorphic nuclei, prominent nucleoli, and ill-defined cytoplasm. STCCs of variable sizes were present in abundance in 10 cases, and numerous NTCN were noted in 12 cases. In two HCCs, the tumor cells with well-defined cytoplasm were present singly and in cohesive sheets, and no STCCs or NTCN were observed. Thus, the presence of small tumor cells with ill-defined cytoplasm and prominent nucleoli in syncytial clusters and abundant NTCN in the FNA of a thyroid nodule should alert the observer about the strong possibility of an HCC.