Analysis of patterns and risk factors regarding the onset of nodules in the contralateral thyroid lobe during follow-up ultrasonography among patients after unilateral lobectomy for the treatment of papillary thyroid carcinoma

Background: This study tries to find the patterns of new nodules in contralateral thyroid lobe among papillary thyroid carcinomas (PTCs) after lobectomy using ultrasonography. Methods: Of note, 456 PTCs were enrolled. Clinicopathological features of primary tumors and sonographic patterns of new nodules in contralateral lobe were documented. Logistic regression analysis was performed to identify risk factors for new nodules. Results: The overall incidence of new nodules was 41.9%. 96.3% of new nodules were no greater than 1 cm while only 10.5% of those were with high suspicion of malignancy. There was no difference in the incidence and sonographic patterns of new nodules between patients with an original tumor size <1 cm (n = 267) vs 1 to 4 cm (n = 189). Multivariate logistic regression analysis showed age (OR, 1.021; 95% CI, 1.001-1.041; P = .036) played risk factor for new nodules while tumor size >1 cm did not. Conclusion: New nodules in the contralateral lobe were common, but usually small and benign by ultrasound features. Older age was found to be a risk factor to predict new nodules. This study supports lobectomy for 1-4 cm PTC in terms of incidence of new nodules on the remnant lobe.