Malignancy rate in nondominant nodules in patients with multinodular goiter: Experience with 1,606 cases evaluated by ultrasound-guided fine needle aspiration cytology

Background: Conventional medical sources recommend the use of fine needle aspiration cytology (FNAC) for single thyroid nodules and the dominant nodule in multinodular goiter (MNG). The purpose of the present study was to analyze the utility of FNAC for multiple thyroid nodules in patients with MNG and to determine the rate of malignancy in teh nondominant nodules. Materials and Methods: Our private practice performed ultrasound-guided FNAC on 1,606 patients between February 2001 and February 1, 2010. In the MNG cases, samples were taken from the dominant nodule and from trhee suspicious / nonsuspicious nodules larger than 1 cm on ultrasound. Ninety-four cases were diagnosed as ‘suspiciously malignant’(SUS) or ‘malignant’ (POS) based on FNAC. Results: The rate of an SUS / POS diagnosis was 5.7% in the dominant nodules; 2.3% of the nondominant nodules had a SUS / POS diagnosis in FNAC (p = 0.0003). Follow-up revealed malignancy in 15 (35.7%) nondominant nodules and in 27 (64.2%) dominant nodules, with 42 MNG cases undergoing surgery. X test showed a ‘p-level of 0.0003’ between the percentages of SUS / POS diagnosis in dominanat and nondominanat nodules. It was less than the significance level of 0.05. Therefore, the result was regarded to be statistically significant. Conclusions: Nondominant nodules could harbor malignancy. The risk of malignancy in nondominant nodules in MNG should not be underestimated. We have shown that the dominant nodule in patients with MNG was in fact about 2.5 times more likely to be malignant than a nondominant nodule. The use of FNAC for nondominant nodules could enhance the likelihood of detecting malignancy in an MNG.