Risk of Malignancy in Bethesda Category III and IV Thyroid Nodules

Abstract

Background: The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) provides a standardized framework for thyroid fine-needle aspiration cytology (FNAC). Bethesda Category III (Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance) and Category IV (Follicular Neoplasm/Suspicious for Follicular Neoplasm) represent indeterminate thyroid nodules with variable risks of malignancy, creating challenges in clinical management.
Aim: To determine the risk of malignancy in Bethesda Category III and IV thyroid nodules and correlate cytological findings with final histopathological diagnosis.
Methods: A prospective observational study was conducted at Rabindranath Tagore Medical College, Udaipur, Rajasthan, from March 2024 to March 2026. Eighty patients diagnosed with Bethesda Category III or IV thyroid nodules who subsequently underwent surgery were included. Histopathological examination served as the gold standard for diagnosis. The malignancy rates in both Bethesda categories were analyzed.
Results: Among 80 patients, 45 (56.3%) belonged to Bethesda Category III and 35 (43.7%) to Category IV. Histopathological examination revealed malignancy in 14 (31.1%) Category III nodules and 18 (51.4%) Category IV nodules. Papillary thyroid carcinoma was the most common malignancy. Category IV nodules demonstrated a significantly higher risk of malignancy compared to Category III nodules (p=0.041).
Conclusion: Bethesda Category IV thyroid nodules carry a significantly higher risk of malignancy than Category III nodules. Histopathological evaluation remains essential for definitive diagnosis and appropriate surgical management.