A clinical-ultrasound-CT nomogram for central lymph node metastasis in papillary thyroid microcarcinoma

Background Central lymph node metastasis (CLNM) is common in papillary thyroid microcarcinoma (PTMC) but its preoperative prediction remains challenging. We developed a nomogram combining clinical, ultrasound (US), and contrast-enhanced computed tomography (CT) features for CLNM in PTMC. Methods In this single-center retrospective study, 162 PTMC patients who underwent thyroidectomy with central lymph node dissection between November 2022 and November 2025 were included. Patients were divided into CLNM-positive (n = 73) and CLNM-negative (n = 89) groups based on postoperative pathology. Preoperative clinical data, US features, and CT signs were evaluated. Least Absolute Shrinkage and Selection Operator (LASSO) regression and multivariate logistic regression were applied for predictor selection and model construction. Internal validation used 1000 bootstrap resamples stratified by outcome; apparent and optimism-corrected performance were reported. Results Of the 162 patients, 73 (45.06%) had pathologically confirmed CLNM; this represents the observed prevalence in this surgically selected cohort and is not an estimate for the general PTMC population. Multivariate analysis identified seven independent risk factors: male sex (OR = 2.278), maximum diameter (per 1-mm increase, OR = 1.332), microcalcification (OR = 2.962), capsular invasion/contact ≥25% (OR = 3.171), ill-defined margin on US (OR = 2.394), “cookie-bite” sign with protrusion on CT (OR = 2.670), and post-contrast blurred margin on CT (OR = 2.522). The apparent AUC was 0.901 (95% CI 0.850-0.952), and the bootstrap optimism-corrected AUC was 0.876 (95% CI 0.821-0.931; optimism 0.025). Calibration was acceptable (corrected slope 0.94, 95% CI 0.78-1.10; Hosmer-Lemeshow P = 0.42), and decision curve analysis showed net benefit over threshold probabilities of 0.10-0.70. Conclusion This preliminary nomogram combining US and CT morphological features with clinical predictors may aid preoperative risk stratification for CLNM in PTMC. Because of the single-center retrospective design and lack of external validation, findings are exploratory and require validation before clinical use.