Parathyroid adenoma diagnosed as papillary carcinoma of thyroid on needle aspiration smears

Needle aspiration of a neck mass was performed on a 55-year-old white female with hypercalcemia. The cytologic material showed cohesive clusters of monomorphic hyperchromatic cells resembling follicular cells. Papillary formation and follicle-like arrangements suggested papillary carcinoma of the thyroid. The histopathologic section of the excised mass, however, revealed a parathyroid adenoma. The diagnostic difficulties in differentiating parathyroid adenoma from well-differentiated thyroid carcinoma are discussed. Data published in the literature emphasize similar difficulties, and it is concluded that a final diagnosis can be established only on histopathologic sections.