Unsuspected intrathyroidal parathyroid adenoma: Mimic of lymphocytic thyroiditis in fine-needle aspiration specimens - A case report

Fine-needle aspirations (FNAs) of parathyroid adenomas (PA) are infrequentl y encountered, brit the scant literature oil this topic emphasizes the diff iculties in distinguishing them from thyroid neoplasms. We report on a case of an unsuspected intrathyroidal PA whose two FNA specimens mimicked almos t perfectly the features of lymphocytic thyroiditis (LT). The smears from t wo FNAs of a "thyroid nodule" ill a 22-yr-old woman were received with a cl inical diagnosis of "LT." The cytological features of both specimens were s imilar and consisted of groups of epithelial cells in a background of numer ous "naked" nuclei, interpreted as Hurthle cells and lymphocytes respective ly and leading to a cytological diagnosis of LT. Subsequent surgical excisi on of the "nodule" revealed a large intrathyroidal PA. The oxyphil cells an d chief cells (the latter devoid of cytoplasm) present in the PA resembled Hurthle cells and lymphocytes respectively: in the FNA specimens. In conclu sion, PA carl give a cytological picture almost identical to that of LT in FNA material. Important clues to the diagnosis of PA in FNA specimens inclu de the presence sf prominent capillaries and the knowledge of a clinical hi story of hyperparathyroidism. (C) 1999 Wiley-Liss,Inc.