Correlation between ultrasound findings of thyroid imaging reporting and data system II and III thyroid nodules and fine-needle aspiration results

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Background and objectives Thyroid nodules are common clinical findings, and their detection rate is increasing owing to the widespread use of high-resolution ultrasonography. Accurate risk stratification is essential to avoid unnecessary, invasive procedures. The American College of Radiology Thyroid Imaging Reporting and Data System (ACR-TIRADS) was developed to standardize ultrasound evaluation and guide the need for fine-needle aspiration (FNA). This study aimed to evaluate the correlation between ultrasound-based ACR-TIRADS II and III classifications and fine-needle aspiration cytology (FNAC) results using the Bethesda System. Patients and methods A prospective observational cross-sectional study was conducted at Sulaymaniyah Teaching Hospital between December 2024 and December 2025. Ninety adults with thyroid nodules classified as ACR-TIRADS II ( n = 27) or III ( n = 63) who underwent ultrasound-guided FNA as part of routine clinical care were included. Cytology was categorized using the Bethesda System. The primary analysis assessed the distribution of Bethesda categories by TIRADS group; Bethesda V-VI was additionally evaluated as a high-risk cytology endpoint rather than as histopathologically confirmed malignancy. Results Bethesda II cytology was more frequent in ACR-TIRADS II than ACR-TIRADS III nodules (88.9% vs 54.0%; Fisher exact P = 0.002). Bethesda V-VI cytology occurred in 3.7% of ACR-TIRADS II and 17.5% of ACR-TIRADS III nodules (Fisher exact P = 0.099). The overall 2×6 ACR-TIRADS-Bethesda System distribution did not reach conventional statistical significance (Pearson χ 2 = 10.67, df = 5, P = 0.058). Using ACR-TIRADS III as the positive category for predicting Bethesda V-VI cytology yielded a sensitivity of 91.7% (95% CI 61.5–99.8), specificity of 33.3% (23.1–44.9), PPV of 17.5% (9.1–29.1), NPV of 96.3% (81.0–99.9), and overall accuracy of 41.1% (30.8–52.0). Conclusions In this selected cohort of biopsied low-risk nodules, TIRADS II was predominantly associated with benign cytology, while TIRADS III showed a higher proportion of Bethesda V-VI outcomes. These findings support the value of ACR-TIRADS as a risk-stratification framework, but they should not be interpreted as evidence to omit or mandate FNA outside established size and clinical criteria because histopathological confirmation and longitudinal follow-up were not available.