Assessing the rate of malignancy in Bethesda category III thyroid nodules and its correlation with histopathology

• Author Details:   
• Lakshmi Agarwal ^*
• Hitisha Kumawat
• Kalpit Jain
• Manmohan Agrawal

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Background: Fine-needle aspiration cytology (FNAC) is a key diagnostic tool for evaluating thyroid nodules. The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) classifies thyroid nodules into six categories, with Category III (Atypia of Undetermined Significance - AUS) presenting diagnostic challenges due to its variable malignancy risk, reported between 13% and 30%. This study aims to assess the malignancy risk of Bethesda Category III nodules and analyse the role of cytological and radiological features in malignancy prediction.

Materials and Methods: Retrospective study was conducted on 20 patients diagnosed with Bethesda Category III thyroid nodules on FNAC who subsequently underwent surgical resection. FNAC slides were re-evaluated to assess cytomorphological features such as nuclear atypia, chromatin changes, microfollicular patterns, colloid presence, and lymphocytic infiltration. Histopathological findings were correlated with FNAC results to determine malignancy rates. Additionally, sonographic features such as echogenicity, vascularity, and the presence of calcifications were analysed to assess their predictive value for malignancy.

Results: Among the 20 cases, 35% (7/20) were malignant, while 65% (13/20) were benign. The malignant cases included follicular carcinoma (n=4) and the follicular variant of papillary carcinoma (n=3). The benign cases consisted of nodular goiter (n=6), follicular adenoma (n=6), and Hashimoto thyroiditis (n=1). Hypoechogenicity and irregular margins were observed in 5 malignant cases, and one case demonstrated microcalcifications. FNAC features such as nuclear grooves, chromatin pallor, and microfollicular patterns were significantly associated with malignancy.

Conclusion: Malignancy risk of Bethesda Category III thyroid nodules may be higher than traditionally estimated in the present study. A multidisciplinary approach, integrating cytological, radiological, and clinical findings, is crucial for guiding patient management, including repeat FNAC, molecular testing, or surgical intervention. Due to the limited sample size, further large-scale, multicenter studies are warranted to validate these findings and optimize diagnostic strategies.

Keywords: TBSRTC, AUS, FNAC, Histopathology, ROM.