Development and validation of a predictive nomogram for cervical lymph node metastasis in aspect ratio ≥1 papillary thyroid carcinoma using ultrasonic features and serum calcitonin.

BACKGROUND: Preoperative prediction of cervical lymph node metastasis (CLNM) remains challenging in patients with papillary thyroid carcinoma (PTC) exhibiting an aspect ratio ≥1, a subgroup in which ultrasound alone has limited sensitivity (approximately 50%) and no dedicated predictive model currently exists. This study aimed to develop and internally validate a predictive nomogram combining ultrasonic features and serum calcitonin for CLNM in this specific population. METHODS: This retrospective study consecutively enrolled 156 patients with aspect ratio ≥1 PTC who underwent thyroidectomy and neck lymph node dissection at a single center (November 2023 to June 2025). The gold standard outcome was pathologically confirmed CLNM. Forty-six candidate predictors (clinical, ultrasonographic, and serological variables) were collected. Predictor selection was performed using least absolute shrinkage and selection operator (LASSO) regression with 10-fold cross-validation, followed by multivariate logistic regression. A nomogram was constructed and internally validated using 1,000 bootstrap resamples. Model performance was assessed by area under the curve (AUC), calibration curve, sensitivity, specificity, and decision curve analysis (DCA). RESULTS: Among 156 patients [116 females, 40 males; median age 52 years, interquartile range (IQR), 45-57 years], CLNM was present in 48 patients (30.8%). Five independent predictors were identified: multifocality [odds ratio (OR) =5.87; 95% confidence interval (CI): 1.85-18.66], maximum diameter ≥1 cm (OR =11.57; 95% CI: 2.26-59.16), ill-defined margin (OR =7.43; 95% CI: 2.06-26.76), microcalcifications (OR =3.43; 95% CI: 1.19-9.93), and serum calcitonin (OR =1.44; 95% CI: 1.08-1.92 per pg/mL). The nomogram achieved an apparent AUC of 0.834 (95% CI: 0.767-0.901) and a bootstrap-corrected AUC of 0.813. At the optimal probability cutoff of 0.264, sensitivity was 81.2% and specificity 75.9%. Calibration showed good agreement (Hosmer-Lemeshow P=0.41), and DCA demonstrated net clinical benefit across a threshold probability range of 5-80%. CONCLUSIONS: This nomogram combining five preoperative predictors shows satisfactory discriminative ability for CLNM in patients with aspect ratio ≥1 PTC. However, given the single-center design, modest sample size, and lack of external validation, these findings should be considered preliminary. External validation in independent multicenter cohorts is required before clinical application.