The thyroid gland is a midline structure located in the anterior neck. The thyroid functions as an endocrine gland and is responsible for producing thyroid hormone and calcitonin (1). Among the radiologic procedures, High Resolution Ultrasonography (HRUS) is a sensitive, relatively inexpensive, non-invasive and an easily accessible modality of imaging for examination of thyroid gland (2). Due to its superficial location, ultrasonography (USG) plays an important role in assessing pathologies in the gland (2) hence Ultrasonography is the modality of choice for initial characterization of a thyroid nodule (3) . Thyroid nodule is any lesion in the thyroid gland that is discrete and is radiologically distinct from the surrounding thyroid parenchyma (4). Features like irregular margins, internal vascularity and microcalcifications can point towards "suspicious" thyroid nodules (5). Though the prevalence of thyroid nodule can reach up to 67% in general population (on HRUS) and 5% of these are malignant (6). Thyroid cancer is the most common endocrine malignancy and, in 2018, it globally constituted 3.3% of all neoplasms (7). Incidence rates of thyroid cancer have been increasing in the last decades worldwide, both in high-resource (8) and in low- or middle-income countries (9). Thyroid swellings are frequently encountered in clinical practice. Clinical evaluation helps in early diagnosis but it is difficult to differentiate early malignant lesions from the most prevalent benign conditions. Ultrasound is a widely available, highly sensitive imaging modality for detection and characterization of thyroid nodule (10). Hence there is a need for standardizing the reporting system for thyroid nodules to allow a better report which is easily reproducible and would facilitate better patient management based on their risk of malignancy. Thyroid Imaging Reporting and Data System (TIRADS) is a classification system for thyroid nodules, which classify them into benign or malignant, based on ultrasound characteristics. Still histopathological examination is the gold standard for the classification of thyroid swellings (10). Among many classifications American College of Radiology Thyroid Imaging Reporting and Data System (ACR TIRADS) is most widely used classification which involves 23 Ultrasonography (USG) features with different weighting (11). Among other classifications Korean TIRADS (K TIRADS) involve fewer Ultrasound(US) features than that of the ACR-TIRADS (12) which uses a pattern-based system instead of an individual US feature-based system or a point-based system (13). In India only few studies are conducted to compare the diagnostic efficacy of various TIRADS classification. This study aims to assess the accuracy of ACR TIRADS (American College of Radiology) and Korean TIRADS classification in the evaluation of thyroid swellings by comparing with cytological examination /Histopathological reports. AIMS AND OBJECTIVES 1. To classify thyroid nodules according to ACR TI-RADS and Korean TI-RADS. 2. To stratify thyroid nodules into benign and malignant categories based on ultrasound findings. 3. To compare the Diagnostic performance of ACR TIRADS and KOREAN TIRADS with Fine needle aspiration cytology (FNAC) /Histopathology as Gold standard.

A prospective observational comparative study was conducted in the Department of Radiodiagnosis at Kidwai Memorial Institute of Oncology in collaboration with the Departments of General Surgery, ENT, and Pathology. The study was carried out over a period of two years, from December 2020 to December 2022. A total of 100 patients who were referred to the Department of Radiodiagnosis for ultrasound (USG)-guided fine-needle aspiration cytology (FNAC) of thyroid lesions were included in the study. INCLUSION CRITERIA • Patients aged > 10 and <80 years with clinically suspicious thyroid nodule. • Minimum diameter of thyroid nodule more than or equal to 5mm. EXCLUSION CRITERIA • Patient who is unable to lie down for ultrasound. • Patient with thyroid nodule who is refusing for USG guided FNAC. • Post-surgical cases. • Post Radiotherapy. • Inconclusive /unsatisfactory histopathology report. • Diffuse thyroid disease. METHODS Ultrasound Technique All patients underwent high-resolution ultrasonography using a high-frequency linear transducer (7.5–15 MHz). Each thyroid nodule was evaluated for composition ,Echogenicity,Shape ,Margin ,Echogenic foci ,Cervical lymphadenopathy .Each lesion was independently categorized according to both ACR TI-RADS and Korean TI-RADS criteria. Reference Standard Ultrasound findings were compared with FNAC reports and histopathological examination wherever surgery was performed. Histopathology was considered the definitive reference standard whenever available. Statistical Analysis Data were entered into Microsoft Excel and analysed using appropriate statistical software. Diagnostic performance of both classification systems was evaluated by calculating sensitivity, specificity, positive predictive value, negative predictive value, overall accuracy, and receiver operating characteristic (ROC) analysis wherever applicable. A p-value <0.05 was considered statistically significant.

Patient Characteristics A total of 100 consecutive patients with thyroid nodules were included in this prospective study. All patients underwent high-resolution ultrasonography followed by US-guided FNAC.The study population had a mean age of approximately 50 years, with the highest frequency of thyroid nodules occurring during the fourth decade of life. Females constituted the majority of the study population, whereas the proportion of malignant nodules was relatively higher among male patients. Ultrasound Characteristics The ultrasound appearance differed significantly between benign and malignant nodules. • Benign nodules were predominantly mixed solid-cystic lesions with isoechoic echogenicity, smooth margins, and wider-than-tall orientation(Figure 1 and 2). • Malignant nodules were more frequently solid, hypoechoic, demonstrated irregular/lobulated margins, microcalcifications, extrathyroidal extension, and taller-than-wide configuration(Figure 3). Risk Stratification by ACR TI-RADS As per ACR TIARDS majority of nodules were categorized as TIRADS IV (37 % ) .Among TIRADS IV category 48.6%(18 of 37) nodules were benign and 52.4% (19 of 37 ) were malignant.Only 4 % nodules were categorized as TIARDS I and all of them were benign on FNAC.Among TIRADS V nodules 10.3 % (3 of 29 ) were benign and 89.7 % (26 of 29 ) were malignant.In our study, considering FNAC/histopathology as gold standard the malignancy risk for TIRADS I was 0%, TIRADS 2 was 6.2% ,TIRADS 3 was 7.1% , TIRADS 4 was 51.3 % and TIRADS 5 was 89.6%. Hence TIRADS I has no risk of malignancy and TIRADS V has highest risk of malignancy(Table 1). TABLE 1: MALIGNANCY RISK STRATIFICATION OF THYROID NODULES BASED ON ACR TIRADS. ACR TIRADS BENIGN MALIGNANT Total I 4 0 4 II 15 1 16 III 13 1 14 IV 18 19 37 V 3 26 29 Grand Total 53 47 100 Risk Stratification by Korean TI-RADS According to Korean TIRADS majority of nodules were categorized as TIRADS IV (36 % ). Among TIRADS IV category 63.8%(23 of 36) nodules were benign and 36.1% (13 of 36 ) were malignant. TIRADS category I refers to no nodule according to K TIRADS. 6 % nodules were categorized as TIARDS II and all of them were benign on FNAC.Among TIRADS V nodules 5.8 % (2 of 34 ) were benign and 94.1 % (32 of 34) The malignancy risk for TIRADS II was 0%, TIRADS 3 was 8.3% , TIRADS 4 was 36 % and TIRADS 5 was 94.1 %. Hence with increasing TIRADS category there is increased risk of malignancy(Table 2) . TABLE 2 : MALIGNANCY RISK STRATIFICATION OF THYROID NODULES BASED ON KOREAN TI-RADS KOREAN TIRADS BENIGN MALIGNANT Grand Total II 6 0 6 III 22 2 24 IV 23 13 36 V 2 32 34 Grand Total 53 47 100 Comparative Diagnostic Performance : Both ACR TI-RADS and Korean TI-RADS demonstrated identical sensitivity (95.7%) for detecting malignant thyroid nodules. However, ACR TI-RADS showed superior specificity (60.3% vs. 52.8%), positive predictive value (68.1% vs. 64.2%), negative predictive value (94.1% vs.93.3%),and overall diagnostic accuracy (77% vs. 73%). Although receiver operating characteristic (ROC) analysis demonstrated good diagnostic performance for both systems, both classifications proved effective for risk stratification of thyroid nodules(Table 3). TABLE 3 : Comparative Diagnostic Performance of ACR and Korean TIRADS STATISTICAL ANALYSIS PARAMETER ACR TIRADS KOREAN TIRADS Sensitivity 95.8% 95.7% Specificity 60.3% 52.8% Positive Predictive Value 68.1% 64.2% Negative Predictive Value 94.1% 93.3% Diagnostic Accuracy 77% 73% P Value <0.001 <0.001

The present prospective study compared the diagnostic performance of the ACR TI-RADS and K-TIRADS in the evaluation of thyroid nodules, using cytopathology and histopathology as the reference standards. Both classification systems demonstrated excellent sensitivity for identifying malignant thyroid nodules and proved to be effective risk stratification tools in routine clinical practice (14-17) . A total of 100 thyroid nodules were evaluated. The majority of patients were females, with most presenting during the fourth and fifth decades of life. These findings are consistent with the established epidemiology of thyroid nodules, which occur more frequently in women owing to hormonal influences and the higher prevalence of benign thyroid disorders (18,19) . Similar demographic patterns have been reported by Tessler et al. (14), Kwak et al.(15 ), and Ha et al.(16). In the present study, solid composition, marked hypoechogenicity, irregular or lobulated margins, microcalcifications, and a taller-than-wide configuration were significantly associated with malignant thyroid nodules. These ultrasound characteristics are well-established predictors of malignancy and constitute the basis of both the ACR TI-RADS and K-TIRADS classification systems (14-16,20). Similar observations have been reported by Kwak et al.(15) , Russ et al. (20) , and Middleton et al. (21) , who demonstrated that these sonographic features have strong predictive value for thyroid carcinoma. The risk of malignancy increased progressively with increasing ACR TI-RADS category. Nearly all nodules categorized as TR1 and TR2 were benign, whereas TR5 nodules demonstrated the highest probability of malignancy. This progressive increase confirms the effectiveness of the ACR TI-RADS scoring system in stratifying thyroid nodules according to malignant potential (14,21,22).Similar trends have been demonstrated in the original ACR TI-RADS validation study and subsequent multicentre investigations. Likewise, K-TIRADS demonstrated a stepwise increase in malignancy rates from K-TR2 to K-TR5. Nearly all K-TR5 nodules in the present study were malignant on cytopathological evaluation. These findings are in agreement with those of Ha et al.(16), who reported that K-TIRADS provides excellent sensitivity for detecting thyroid malignancy while maintaining a simple pattern-based classification. The primary objective of this study was to compare the diagnostic performance of both classification systems. ACR TI-RADS demonstrated a sensitivity of approximately 95.7%, specificity of 60.3%, positive predictive value of 68.1%, negative predictive value of 94.1%, and an overall diagnostic accuracy of 77%. K-TIRADS demonstrated the same sensitivity but slightly lower specificity (52.8%) and overall diagnostic accuracy (73%). These findings indicate that both systems are highly effective in identifying malignant nodules, whereas ACR TI-RADS offers superior specificity and may reduce unnecessary fine-needle aspiration cytology (FNAC), consistent with previous comparative studies (22-24). The higher specificity observed with ACR TI-RADS may be attributed to its point-based scoring system, which provides balanced weighting of individual ultrasound features. In contrast, K-TIRADS uses a pattern-recognition approach that categorizes a larger proportion of nodules into higher-risk groups, thereby improving sensitivity at the expense of specificity. Similar findings have been reported by Grani et al. (22), Yoon et al. (23), and Kim et al.(24). One of the principal clinical advantages of ACR TI-RADS is its ability to reduce unnecessary FNAC procedures without significantly compromising cancer detection. Since benign thyroid nodules constitute the majority of lesions encountered in clinical practice, avoiding unnecessary invasive procedures reduces patient anxiety, healthcare expenditure, and procedure-related morbidity(14,21,22). The findings of the present study support the recommendation that ACR TI-RADS may be preferred when minimizing unnecessary biopsies is a clinical priority while maintaining high diagnostic accuracy. Conversely, K-TIRADS demonstrated equally high sensitivity for malignant nodules and may be advantageous in settings where maximizing cancer detection is prioritized. Although specificity was slightly lower, this trade-off may be acceptable in institutions adopting a more aggressive biopsy strategy. Therefore, selection of the appropriate reporting system should be guided by institutional protocols, patient characteristics, and the desired balance between maximizing cancer detection and minimizing unnecessary FNAC (16,23). The findings of the present study are consistent with previously published literature evaluating ultrasound-based thyroid risk stratification systems. Most published studies have reported sensitivities ranging from 90% to 98% for both ACR TI-RADS and K-TIRADS, with ACR TI-RADS generally demonstrating superior specificity (21-24). The results of the present study further validate the usefulness of these standardized reporting systems in the Indian population. Overall, both ACR TI-RADS and K-TIRADS demonstrated excellent diagnostic performance and significant agreement with cytopathological findings. Standardized ultrasound reporting improves communication among radiologists, endocrinologists, surgeons, and pathologists while facilitating uniform patient management and appropriate selection of patients for FNAC. LIMITATIONS The present study has certain limitations. First, it was conducted at a single tertiary care centre with a relatively modest sample size, which may limit the generalizability of the findings. Second, histopathological confirmation was not available for all thyroid nodules, and FNAC served as the reference standard in many cases. Third, interobserver variability in ultrasound interpretation was not evaluated. Finally, long-term follow-up of benign thyroid nodules was not performed. Larger multicentric studies with long-term follow-up are required to further validate the comparative performance of these risk stratification system .

Both ACR TI-RADS and Korean TI-RADS are effective and reliable ultrasound-based risk stratification systems for thyroid nodules, demonstrating excellent sensitivity for the detection of malignancy. However, ACR TI-RADS showed better specificity, higher positive predictive value, and superior overall diagnostic accuracy compared with Korean TI-RADS in the present study. The use of standardized reporting systems facilitates uniform interpretation of ultrasound findings, improves communication among clinicians, and assists in selecting appropriate patients for fine-needle aspiration cytology. Based on the findings of this study, ACR TI-RADS appears to be a more suitable risk stratification system for routine clinical practice because of its better ability to reduce unnecessary biopsies while maintaining high diagnostic performance.

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