Thyroid nodules are frequently encountered in clinical practice, with an estimated prevalence of 19–68% in the general population, largely due to the increased use of high-resolution imaging techniques [1]. Although most thyroid lesions are benign, distinguishing malignant from benign nodules remains a critical aspect of thyroid pathology. Fine-needle aspiration cytology (FNAC) is widely recognized as the first-line diagnostic modality for evaluating thyroid nodules due to its safety, cost-effectiveness, and minimally invasive nature. It allows preoperative risk stratification and plays a pivotal role in determining the need for surgical intervention [2]. The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), introduced to standardize cytological reporting, has undergone revisions to improve risk stratification and clinical management [3,4]. Despite these advancements, FNAC has limitations, particularly in indeterminate categories where diagnostic ambiguity persists [5]. Histopathological examination remains the gold standard for definitive diagnosis, particularly in cases undergoing surgical excision. Cytohistological correlation is essential to evaluate the diagnostic accuracy of FNAC, identify discordant cases, and improve diagnostic reliability. This correlation also aids in auditing cytology practices and refining criteria for borderline or challenging categories [6]. The present study aims to assess the cytohistological concordance of thyroid lesions in a tertiary care setting, evaluate the diagnostic performance of FNAC using the updated Bethesda classification, and identify key areas of diagnostic discrepancy.

This retrospective study was conducted in the Department of Pathology, Government Medical College, Nalgonda, Telangana, over a two-year period from January 2021 to December 2023.A total of 60 patients with thyroid swellings who underwent FNAC followed by thyroidectomy were included. Cases with inadequate FNAC smears (Bethesda I) or lacking histopathological follow-up were excluded. Cytology Procedure FNAC was performed using a 23-gauge needle under aseptic precautions. Smears were stained with May-Grünwald Giemsa (MGG) and Hematoxylin and Eosin(H&E). Cytological findings were classified according to TBSRTC 2023 into six categories (I–VI). Histopathology Thyroidectomy specimens were fixed in 10% neutral-buffered formalin and processed using standard paraffin-embedding techniques. Sections were stained with hematoxylin and eosin (H&E) and diagnosed according to the WHO Classification of Thyroid Tumours, 5th edition (2022).(6) Statistical Analysis Cytological and histopathological diagnoses were compared. Bethesda Categories V and VI were considered cytologically malignant, and Category II was considered benign. Categories III and IV were excluded from performance calculations. Sensitivity, specificity, PPV, NPV, and diagnostic accuracy were calculated using histopathology as the reference standard.

A total of 60 patients with thyroid swellings were included in the study. The female-to-male ratio was 5:1, with 50 females (83.3%) and 10 males (16.7%). The age of patients ranged from 18 to 70 years, with a mean age of 41.5years. The most common age group affected was 41–50 years (33.3%). Table 1: Cytological Classification (TBSRTC 2023) All FNAC smears were categorized according to the updated Bethesda System for Reporting Thyroid Cytopathology (TBSRTC, 2023). The distribution of cases is shown below Bethesda Category Cytological Diagnosis No. of Cases (%) I Nondiagnostic/Unsatisfactory 0 II Benign 33 (55%) III Atypia of Undetermined Significance (AUS/FLUS) 3 (5%) IV Follicular Neoplasm/Suspicious for FN 4 (6.7%) V Suspicious for Malignancy 8 (13.3%) VI Malignant 12 (20%) Total 60 (100%) Histopathological Diagnosis-All patients underwent thyroidectomy, and histopathological evaluation was performed. The histopathological diagnoses are detailed below: Table 2: Histopathological Spectrum of Thyroid Lesions Histopathological Diagnosis No. of Cases (%) Nodular goiter 25 (41.7%) Colloid goiter with cystic change 5 (8.3%) Hashimoto thyroiditis 3 (5%) Follicular adenoma 7 (11.7%) Papillary thyroid carcinoma (PTC) 15 (25%) Follicular variant of PTC (FVPTC) 3 (5%) Follicular carcinoma 2 (3.3%) Total 60 (100%) Table 3: Correlation between Cytology and Histopathology Bethesda Category No. of Cases Concordant Discordant Correlation Rate (%) II (Benign) 33 31 2 (Malignant on HPE) 93.9% III (AUS/FLUS) 3 1 2 — IV (FN/SFN) 4 3 1 — V (Suspicious) 8 7 1 (benign on HPE) 87.5% VI (Malignant) 12 11 1 91.7% These findings demonstrate a high degree of concordance in clearly benign and malignant categories, while indeterminate categories (III and IV) showed variable correlation, reflecting their inherent diagnostic uncertainty. Table 4: Cross-tabulation of Cytological and Histological Diagnoses Cytological category Malignant on Histopathology(n) Benign on Histopathology(n) Total(n) Malignant (V + VI) 18(True Postive) 2 (False Positive) 20 Benign (II) 2 (False Negative) 31 ((True negative) 33 Total 20 33 53 Note: Indeterminate categories Bethesda III (AUS/FLUS, n = 3) and IV (FN/SFN, n = 4) were excluded from this correlation to focus on definitive benign and malignant diagnoses. Table 4- demonstrates the correlation between cytological and histopathological findings, focusing on Bethesda categories II (Benign), V (Suspicious for malignancy), and VI (Malignant). A total of 20 cases were reported as malignant on FNAC (Bethesda V and VI), of which 18 were confirmed malignant on histopathology (true positives), while 2 were benign (false positives). Among the 33 cases categorized as benign cytologically (Bethesda II), 31 were concordant with histopathology (true negatives), whereas 2 cases were found to be malignant (false negatives).This distribution highlights the diagnostic accuracy of FNAC in differentiating benign from malignant thyroid lesions and forms the basis for calculating sensitivity, specificity, and other performance parameters. Descriptions of Discordant Cases True Positives (TP = 18): These were cases reported as malignant or suspicious for malignancy on FNAC (Bethesda V or VI) and confirmed to be malignant on histopathology. Most included classic papillary carcinoma and its follicular variant. False Positives (FP = 2): These were cases diagnosed as suspicious/malignant on cytology but found to be benign on histology. One was a hyperplastic nodule with nuclear atypia; the other was a follicular adenoma mimicking malignancy. True Negatives (TN = 31): These were cytologically benign (Bethesda II) and confirmed as benign on histopathology, including nodular goiter, colloid goiter, and Hashimoto’s thyroiditis. False Negatives (FN = 2): These were reported as benign on FNAC but were malignant on histopathology (cases were papillary thyroid carcinoma one with cystic change, which can obscure typical nuclear features other was a micropapillary carcinoma). Diagnostic Performance of FNAC Table 5: Based on the above correlation, the diagnostic indices of FNAC are as follows: Parameter Value (%) Sensitivity (Sn) 90.00% Specificity (Sp) 93.94% Positive Predictive Value (PPV) 90.00% Negative Predictive Value (NPV) 93.94% Diagnostic Accuracy 92.45%

Fine-needle aspiration cytology (FNAC) remains an essential preoperative diagnostic tool for evaluating thyroid nodules, owing to its minimally invasive nature, cost-effectiveness, and rapid turnaround time [3,4]. The implementation of the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) has standardized thyroid cytology reporting globally, allowing improved risk stratification and clinical decision-making [3-5]. However, despite its widespread use, limitations persist in certain diagnostic categories, particularly in indeterminate lesions such as Bethesda III and IV, where definitive classification remains a challenge [5,6]. Histopathological examination, thus, continues to serve as the gold standard for confirming cytological findings [7,11]. In our study, the majority of thyroid lesions were observed in the third to fifth decades of life, aligning with global trends that show peak incidence of thyroid nodules in middle-aged adults [1,13]. Malignancy was more frequently encountered in younger patients, particularly females under 40, a pattern also noted by Ahmed et al and Shetty et al. [6,13]. In contrast, benign nodules were more prevalent among older individuals, consistent with the natural history of nodular hyperplasia and colloid goiters. This age-related distribution underscores the importance of integrating patient demographics into the risk assessment of thyroid nodules. Several studies, including those by Jung et al. [6] and Joshi [1], suggest that younger patients with suspicious cytological features may warrant a more aggressive diagnostic and therapeutic approach, given the higher prevalence of papillary thyroid carcinoma in this age group. Cytohistological Concordance and Diagnostic Accuracy In our study, cytohistological concordance was highest in Bethesda Categories II and VI, with benign and malignant lesions showing strong agreement between cytological and histopathological diagnoses. These findings are in line with studies by Joshi et.al, Shetty et al., and Sharma et al. [1,7,14], who reported concordance rates above 85% for these categories. The diagnostic sensitivity and specificity of FNAC in our cohort also mirrored those in previous studies, with Mekni et al. [11] reporting 92.5% sensitivity and 93.2% specificity, while Al Dawish et al. [10] observed an overall accuracy of 91.1%. Several studies, including those by Gupta et al. and Ahmed et al [12,13], have further highlighted FNAC’s high positive predictive value (PPV) in Bethesda VI lesions, often exceeding 95%, affirming its utility in guiding surgical decisions. Conversely, false-negative results—mainly in follicular neoplasms and cystic papillary carcinomas—continue to pose diagnostic challenges [2,16] Diagnostic Dilemma in Bethesda III and IV Categories Bethesda categories III (AUS/FLUS) and IV (FN/SFN) are often the most diagnostically challenging, owing to their inherently indeterminate cytological features and overlapping morphology with both benign and malignant entities. In our study, lesions in these categories showed variable histopathological outcomes, reinforcing the limited predictive value of cytology alone. Similar diagnostic uncertainty was reported by Soundarya et al. [2], and Alaus et al. [15], Gowardhan et al [18]who noted malignancy rates ranging from 15% to 35% in AUS/FLUS nodules, and up to 40% in follicular neoplasms. To improve diagnostic clarity, recent literature emphasizes the role of adjunctive tools such as immunocytochemistry and molecular testing. As highlighted by Rossi et al. [5], the integration of molecular markers (e.g., BRAF, RAS, RET/PTC rearrangements) has enhanced risk stratification, particularly in indeterminate categories. However, access to such testing may be limited in many low- and middle-income settings, including parts of India, thus reinforcing the importance of clinicoradiological correlation and multidisciplinary review in these cases [4-6]. Regional and International Comparisons The diagnostic performance of FNAC in our study aligns closely with findings from both regional and international studies. For instance, a retrospective study from Saudi Arabia by Alshahrani et al. [8] demonstrated FNAC sensitivity and specificity of 88.6% and 94.3%, respectively—comparable to our results. Similarly, a recent multicenter study from Tunisia by Mekni et al. [11] confirmed the reliability of FNAC with an overall diagnostic accuracy exceeding 90%. Studies from India, including those by Rashmi et al [9] and Sharma et al. [14], have echoed similar findings, underscoring the consistency of FNAC accuracy across different healthcare settings. Such comparisons highlight that, when performed and interpreted by experienced cytopathologists, FNAC yields reproducible and clinically actionable results. Nonetheless, geographic variability in malignancy rates across Bethesda categories—as noted in the WHO 2022 thyroid tumor classification [6]—emphasizes the need for population-specific risk assessments and context-based adaptation of cytological thresholds. Table-7 Comparison with other similar studies S.No Study Year Place Sample Size (n) Sensitivity (%) Specificity (%) Diagnostic Accuracy (%) 1. Present Study (Ramya S) 2025 Nalgonda, India 60 90 93.94 92.45 2. Joshi PS et al [1] 2022 Maharashtra, India 80 87.5 92.3 90.0 3. Soundarya S et al [2] 2025 Tamil Nadu, India 100 90.0 95.0 92.5 4. Shetty N et al [7] 2023 Karnataka, India 120 85.0 93.0 89.5 5. Mekni A et al[11] 2023 Tunisia 210 92.5 93.8 93.1 6. Ahmed et al.[13] 2022 Pakistan 92 83.30 91.60 87.90 7. Sharma et al.[14] 2023 Madhya Pradesh, India 78 86.40 92.30 89.74 8. Alaus AS et al[15] 2023 Saudi Arabia 152 91.0 95.0 93.4 9. Singh P. et al[19] 2020 North India 70 83.3 100 95.7 This study’s strengths include its cytohistological design, adherence to the updated Bethesda system, and inclusion of all six diagnostic categories. Nevertheless, the retrospective nature, limited sample size in indeterminate categories, and lack of ancillary molecular data constitute key limitations. These are comparable to those cited by Ahmed et al. and Osseis et al. [13,16]. Moving forward, prospective multicenter studies incorporating clinical, radiological, cytological, and molecular parameters are essential to enhance diagnostic precision. Meanwhile, in low-resource settings, regular cyto-histopathology audits and strict implementation of TBSRTC guidelines remain effective and feasible strategies for improving diagnostic outcomes [7]

Fine-needle aspiration cytology (FNAC), guided by the Bethesda System for Reporting Thyroid Cytopathology, remains a highly effective, minimally invasive tool for the initial evaluation of thyroid nodules. Our study demonstrated high diagnostic accuracy, particularly in benign and malignant categories, with substantial cytohistological concordance. However, the indeterminate categories (Bethesda III and IV) continue to pose diagnostic challenges due to overlapping cytological features. Despite these limitations, FNAC provides valuable preoperative guidance, helping to reduce unnecessary surgeries and streamline patient management. Strengthening diagnostic accuracy through regular audits, cytopathologist training, and adherence to standardized reporting systems is vital. Integration of molecular testing and radiological correlation, where feasible, can further enhance risk stratification and clinical decision-making. Ultimately, FNAC continues to serve as a cornerstone in the diagnostic algorithm for thyroid lesions, and its utility can be further optimized through multidisciplinary collaboration and context-specific diagnostic protocols.

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