Purpose

The management of indeterminate thyroid nodules (ITNs; Bethesda III–V) poses significant clinical challenges. This study sought to identify preoperative ultrasound and clinicopathologic predictors of invasive papillary thyroid carcinoma (PTC) among ITNs and to develop a corresponding risk prediction model.

Patients and Methods

In this retrospective study, 494 patients with FNA-confirmed ITNs and postoperative PTC diagnosis were included. Based on pathology confirming extrathyroidal extension and/or lymph node metastasis, patients were classified as invasive PTC (n=141) or non-invasive PTC (n=353). Univariate and multivariate logistic regression analyses identified independent risk factors, and a predictive nomogram was developed and validated.

Results

Male (odds ratio [OR]=2.91, 95% confidence interval [CI]:1.78– 4.76), age ≤ 45 years (OR=1.93, 95% CI:1.23– 3.03), abundant nodule vascularity (OR=4.60, 95% CI:2.42– 8.75), and capsule proximity ≤ 2 mm (OR=3.63, 95% CI:2.15– 6.14) were independent risk factors for invasive PTC, while abnormal thyroglobulin antibody (TgAb) levels reduced risk (OR=0.38, 95% CI:0.18– 0.77). The prediction model achieved an AUC of 0.776 (95% CI:0.728– 0.825) in the training set and 0.759 (95% CI:0.643– 0.874) in validation, with decision curve analysis confirming clinical utility.

Conclusion

An integrated model incorporating sex, age, vascularity, capsule distance, and TgAb status effectively predicts invasive PTC risk in ITNs. The nomogram provides preoperative risk stratification to guide personalized treatment, potentially reducing unnecessary aggressive surgery in low-risk cases while ensuring optimal management of high-risk patients. An interactive online version is available for clinical implementation.