FINE-NEEDLE ASPIRATION OF NORMAL THYROID-TISSUE MAY RESULT IN THE MISDIAGNOSIS OF MICROFOLLICULAR LESIONS

Background. Inadvertent sampling of normal thyroid surrounding a nodul e may occur when clinically inexperienced personnel perform fine-needl e aspiration (FNA) or when a nodule is small. Because the cytologic ch aracteristics of normal thyroid tissue are not well known, we prospect ively studied 42 patients undergoing thyroidectomy. Methods. FNA was p erformed from the grossly normal contralateral lobe during thyroidecto my. Cytopathologists examined the slides without knowing the source of the tissue.Results. FNA of grossly normal thyroid tissue was adequate for interpretation in 32 or 42 patients, and in nine of 42 cases it w as interpreted as unremarkable. However, the remaining specimens were classified as microfollicular lesions (18), mixed macromicrofollicular lesions (three), Hurthle cell lesion (one), and papillary thyroid car cinoma (one). Conclusions. FNA of grossly normal thyroid tissue sugges ted a microfollicular lesion in 18 (56%) patients, a result that would raise the possibility of a follicular carcinoma and often lead to the recommendation for operation. When FNA is performed, normal thyroid t issue surrounding a nodule should be avoided, and the possibility of a sampling error should be considered when a microfollicular pattern is obtained in a patient with a small nodule.