Suspiciously malignant findings on ultrasound after fine needle aspiration biopsy in a thyroid nodule with initially benign ultrasound and cytologic result: to repeat or to follow-up.

PURPOSE: The purposes of this study were to evaluate the incidence of suspiciously malignant change on ultrasound (US) in thyroid nodules after initial benign US and cytologic results and to investigate the associated US characteristics and the management of these nodules. MATERIALS AND METHODS: Among the patients who underwent thyroid fine needle aspiration biopsy (FNAB) from October 2003 to December 2004, 550 patients who had thyroid nodules with initial benign US and cytologic results were included. Reference standards were established by pathologic results, follow-up cytologic results or follow-up US. We evaluated the incidence of morphologic changes to suspiciously malignant US findings of these thyroid nodules after FNAB. We also evaluated the initial US features associated with the nodules showing suspiciously malignant findings on US after FNAB in these patients. RESULTS: Of 550 patients, 28 nodules (5.1%) showed morphologic changes into nodules with suspiciously malignant US findings on follow-up US. All thyroid nodules showing morphologic changes had mixed solid and cystic components (P<.001). Suspiciously malignant changes on US were associated with the percentage of the cystic portion, but all changed nodules were confirmed as benign. CONCLUSION: Follow-up US should be recommended rather than to repeat FNAB for thyroid nodules with initial benign US and cytologic results even if they later develop suspiciously malignant US features after FNAB.ope