Parathyroid proliferations: a source of diagnostic pitfalls in FNA of thyroid

With wide use of fine-needle aspirates (FNA) for investigation of thyroid nodules, a growing number of parathyroid glands are being inadvertently aspirated for cytologic study. Aiming to determine the effectiveness of FNA to differentiate between parathyroid and thyroid lesions, all cases aspirated initially as thyroid nodules and that had a final histologic diagnosis of parathyroid lesion were retrieved from the authors' files and were systematically reviewed to delineate possible specific diagnostic criteria.

From a total of 90,000 FNA diagnoses of thyroid nodules, 4740 cases were isolated for which a final histologic diagnosis was available. Among these, 29 cases with a final histologic diagnosis of a parathyroid lesion were identified and reanalyzed according to the initial cytologic diagnoses. Furthermore, the FNA smears were reviewed, and specific features were recorded.

FNA failed to recognize the parathyroid origin of the lesions in all but 2 cases with known hyperparathyroidism. Most aspirates were misinterpreted either as suspicious for or as thyroid neoplasms because of high cellularity and absence of colloid. Histologically, the lesions proved to be parathyroid hyperplasia, adenoma, or carcinoma. Specific cytologic features are discussed.

A safe differential diagnosis between thyroid and parathyroid disease on morphological ground in cytologic smears is difficult due to overlapping features of these lesions. To avoid surgical mismanagement, it is essential, in every highly cellular lesion seen in the context of a colloid-free background, to consider and report the possibility of a parathyroid lesion, thus enabling the clinician to proceed to a more detailed preoperative evaluation in this direction.