Purpose: Ultrasonography as the first choice for thyroid nodules is still difficult to distinguish between solid follicular thyroid neoplasm (FTN) and solid nodular goiter (NG). We tried to investigate the value of relative size (M/S, M: the maximum diameter of target nodule, S: the maximum diameter of the largest of the remaining nodules) that may help to differentiate FTN from NG.
Methods: T test and chi-square test were used to retrospectively analyze the differences of the clinical and ultrasonographic characteristics between FTN and NG in 422 cases in our hospital. T  test was used to analyze the difference of M/S value in the two kinds of nodules. ROC was used to evaluate the accuracy of M/S value in distinguishing the two.
Results: There were statistically significant differences in age, echogenicity, calcification, peripheral halo and blood supply between the two. The M/S value is not only significantly different in the two kinds of nodules but also can be used as a quantitative indicator to guide ultrasound diagnosis. ROC analysis showed that the cutoff point and AUC of M/S value were 1.94 and 0.709, respectively.
Conclusion: In the ultrasound diagnosis of multiple thyroid nodules, the M/S value can better distinguish FTN and NG. We need to be aware of FTN when the M/S value of the nodule is greater than 2.
Keywords: follicular thyroid neoplasm, nodular goiter, size, ultrasonography