Reevaluation of malignancy risk in nondiagnostic thyroid nodules with long-term follow-up via surgical resection or core needle biopsy: A retrospective study.

[BACKGROUND] Ultrasound-guided fine-needle aspiration (FNA) of various thyroid nodules often yields nondiagnostic results, which reveal a wide range of the risk of malignancy (ROM) and complicate patient management decisions. This ROM variability likely reflects selection bias, given that previous studies frequently excluded patients without histologic follow-up.

[METHODS] This retrospective cohort study included 1269 patients with nondiagnostic thyroid nodules from a total of 10,337 patients who underwent FNA at Asan Medical Center. The ROM was determined on the basis of pathologic findings after core needle biopsy (CNB) or resection.

[RESULTS] The median follow-up period after the initial FNA was 14.14 months (range, 0.03-145.81 months). Histologic follow-up was available for 361 patients (28.4%), with 49 patients (13.6%) having only surgical resection specimens, 252 patients (69.8%) having only CNB specimens, and 60 patients (16.6%) having both resection and CNB specimens. Sixty-four patients were diagnosed with malignancy on the basis of CNB or surgical resection. The ROM in this cohort ranged from 5.0% to 17.7%. The upper limit of the ROM (13.2%) at the 12-month follow-up in this study was the same as the mean ROM (13%) suggested in The Bethesda System for Reporting Thyroid Cytopathology as updated in 2023. Multivariate logistic regression revealed that younger age (p = .013), spiculated margins (p = .010), and hypoechogenicity (p = .001) were independently associated with malignancy.

[CONCLUSIONS] This study aimed to reduce the overestimated upper limit of the ROM in nondiagnostic thyroid nodules, which was previously based solely on rare surgical follow-up results. Using CNB as an ancillary diagnostic tool can help to rapidly characterize initially nondiagnostic thyroid nodules and guide appropriate management.