Diagnostic performance of the ACR TI-RADS classification in identifying and excluding thyroid malignancy: A multi-correlative retrospective study in a South African tertiary hospital

BACKGROUND Nodular thyroid disease is becoming increasingly prevalent worldwide, with the primary aim of evaluation being to exclude malignancy. The ACR TI-RADS classification was designed to stratify the risk of malignancy in thyroid nodules based on sonographic features, thereby guiding biopsy decisions with the aim of reducing the number of unnecessary invasive procedures performed. Fine-needle aspiration cytology remains the preferred diagnostic tool for evaluating thyroid nodules due to its safety profile and cost-effectiveness. However, it can yield non-diagnostic or indeterminate results, resulting in repeat biopsies, which in resource-limited settings precipates poor patient follow-up or missed malignancy. Core needle biopsy, with histological evaluation, has become increasingly recognized as the gold standard for definitive diagnosis, reducing the need for repeat sampling. The aim of this study was to retrospectively assess the diagnostic accuracy of the reported ACR TI-RADS classification in identifying and excluding malignant thyroid lesions using histology as the gold standard of reference, with further secondary correlation with cytology, biochemistry, and nuclear medicine studies where available, at our local setting in Grey’s Hospital, Pietermaritzburg. RESULTS The study group consisted of 68 patients with a mean age of 52.6 years (range, 27–82 years), female predominance and a 16.2% thyroid malignancy rate. For ease of analysis, ACR TI-RADS categories 1–3 were grouped as benign, and categories 4–5 as malignant. Comparison of ACR TI-RADS with histology showed a sensitivity of 63.6%, specificity of 38.6%, positive predictive value of 16.7%, and negative predictive value of 84.6%. Receiver operating characteristic curve analysis showed an area under the curve of 0.51. Among the sonographic features evaluated, the presence of intralesional vascularity was significantly associated with malignancy (p < 0.05), advocating its inclusion into a modified ACR-TIRADS score. CONCLUSION ACR TI-RADS is a valuable tool for thyroid nodule risk stratification, but it demonstrates limitations in sensitivity and specificity within our setting. Discrepancies between the ACR TI-RADS scoring and histology highlights potential over- or under-estimation of malignancy risk, influenced by inter-operator variability and inconsistent reporting. Standardized reporting protocols, ongoing training, and the incorporation of additional sonographic features, such as vascularity assessment, may improve diagnostic performance, thereby reducing patient morbidity and mortality.