High prevalence of carcinoma in ultrasonography-guided fine needle aspiration cytology of thyroid nodules

Objective: The purpose of this study was to assess the rate of malignancy in thyroid nodules incidentally detected at sonography and to determine the diagnostic value of ultrasonography-guided fine needle aspiration cytology (USgFNAC) in thyroid nodules. Methods: Five hundred patients (84 men and 416 women) who had thyroid incidentalomas underwent USgFNAC at Konkuk University Hospital between August 2005 and July 2006. Thyroid sonography and guided aspiration was performed on all single nodules and on dominant nodules with suspected malignancy in cases of multinodular goiter. Results: Five hundred fifty-eight nodules from 500 patients were aspirated using ultrasonography guidance. The USgFNAC results for all patients were as follows: 307 (61.4%) benign, 108 (21.6%) suggestive of malignancy, 56 (11.2%) indeterminate, and 29 (5.8%) inadequate for cytologic diagnosis. The rate of malignancy was significantly higher in women than in men (23.6% in women vs 11.9% in men, p<0.01). Ultrasonographic characteristics that had a significant association with thyroid malignancy included solid echocomponent, hypoechogenecity, ill defined margin, and presence of microcalcifications (p<0.05). Eighty-eight patients underwent surgical resection. The positive predictive value of USgFNAC was 90.2% (74/82), and the accuracy index was 84.1% (74/88). In 80 patients with well-differentiated thyroid carcinoma after surgery, 49% (39/80) had lesions smaller than I cm. Conclusion: The rate of malignancy in incidental thyroid nodules on USgFNAC was 21.6%. Ultrasonographic features could be useful in differentiating between benign and malignant nodules.