Incidental Thyroid Nodules Detected on CT and MRI: Frequency, Ultrasound Risk Stratification, and Clinical Outcomes in a Cross-Sectional Study

Abstract

Background: Incidental thyroid nodules (ITNs) are increasingly detected on computed tomography (CT) and magnetic resonance imaging (MRI) performed for non-thyroid indications. Although most incidental nodules are benign, a small proportion may represent thyroid malignancy, creating challenges regarding appropriate evaluation and management. Understanding the frequency, imaging characteristics, and outcomes of ITNs is important for developing evidence-based diagnostic pathways.

Objective: To determine the frequency of incidental thyroid nodules detected on CT and MRI examinations and to evaluate their ultrasound characteristics, cytological findings, and malignancy outcomes.

Methods: This cross-sectional study reviewed 1,500 CT and MRI examinations that included visualization of the thyroid gland and were performed for non-thyroid clinical indications. Incidental thyroid nodules were identified and characterized according to size, multiplicity, and imaging features. Nodules meeting established criteria underwent dedicated thyroid ultrasonography and were classified using the American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS). Fine-needle aspiration cytology (FNAC) and histopathological findings were reviewed where available. Data were analyzed descriptively using frequencies, percentages, and summary statistics.

Results: Incidental thyroid nodules were identified in 225 of 1,500 examinations, yielding an overall frequency of 15%. The prevalence was 16% on CT and 13% on MRI. The median nodule size was 9 mm (interquartile range: 6–14 mm), and multiple nodules were present in 68 patients (30%). Ninety patients (40%) underwent dedicated thyroid ultrasonography, while 27 patients (12%) underwent FNAC. Among evaluated nodules, 41 (46%) were classified as ACR TI-RADS TR1–TR2, 27 (30%) as TR3, 16 (18%) as TR4, and 6 (6%) as TR5. Only two nodules (2%) were confirmed as malignant on cytological or histopathological examination. The majority of incidental nodules therefore demonstrated low-risk ultrasound characteristics and did not require invasive intervention.

Conclusion: Incidental thyroid nodules are common findings on CT and MRI examinations performed for non-thyroid indications; however, the prevalence of malignancy is low. Most nodules exhibit low-risk ultrasound features and can be managed conservatively. A selective, guideline-based approach incorporating ultrasound risk stratification and targeted FNAC appears effective for identifying clinically significant lesions while minimizing unnecessary investigations and interventions.