Oncocytic parathyroid adenoma: problem in cytological diagnosis.

Parathyroid lesions, which may occur within the thyroid, may clinically simulate thyroid nodules. Fine-needle aspiration (FNA) of these presumably "thyroid nodules" can lead to misinterpretation of cytomorphological findings because of similarities in cytological features of neoplastic and nonneoplastic parathyroid and thyroid lesions. This might be true especially for oncocytic parathyroid adenomas and parathyroid adenomas with prominent oncocytic component that, although rare, tend to be large and often are associated with minimal hyperparathyroidism. We report two cases of this type of clinically "silent" parathyroid adenomas that on FNA were diagnosed as Hurthle cell thyroid neoplasm. 2004 Wiley-Liss, Inc.