The effect of fine-needle aspiration biopsy on the thyroid scan.

Fine-needle aspiration biopsy (FNAB) is the most sensitive and specific procedure in diagnosing benign from malignant thyroid nodular disease. The effects of a FNAB on the thyroid scan, however, have never been studied. This assumes importance because a hot nodule on scan has been advocated as useful to differentiate certain benign from malignant follicular neoplasms. Thyroid scans were performed before and after FNAB on 11 patients with nodular thyroid disease and an area of normal or increased uptake either in the nodule or in a contralateral enlarged lobe to determine if the biopsy changed the pattern of isotope uptake. For this study, biopsies were done in the area of normal or increased uptake. In two patients, there was a reduction in isotope concentration in three nodules after FNAB, whereas no change was demonstrable in nine other patients. Review of the literature revealed a number of prior reports of hemorrhage, necrosis, or infarction of thyroid nodules after FNAB. Based on these data and the demonstration of a change in scan pattern in a patient following FNAB, it is concluded that FNAB may decrease the isotope uptake in thyroid nodules; therefore, the concept of clinical judgments being based on the scan pattern after FNAB should be reevaluated.