Background: Fine needle aspiration cytology (FNAC) reduces the number of unnecessary thyroid surgeries for patients with benign nodules and appropriately triages patients with thyroid cancer to appropriate treatment.

Methods: This was a observational study done on cases presenting with clinical suspicion of thyroid malignancy which underwent ultrasonography followed by FNAC of thyroid nodule. Ultrasonographic characterization of nodules was based on Thyroid Imaging Reporting And Data System (TIRADS) and cytology reporting was based on Bethesda system. All recruited patients underwent thyroidectomy. Pre-operative cytology and ultrasonography features were compared with final histopathology report.

Results: In our study, Bethesda system of cytology reporting for thyroid nodules had a better sensitivity, specificity and diagnostic accuracy than TIRADS system of ultrasound reporting. Bethesda system in FNAC had a larger area under the ROC curve (0.91) as compared to ultrasound TIRADS (0.70). Malignancy rate of TIRADS 5 nodules was 97.1% with significant p value (0.022). 100% of Bethesda VI lesions were malignant according to final histopathology report. Ultrasound TIRADS could pre-operatively predict malignancy in 63.6% of indeterminate thyroid nodules with confirmed malignancy in post-operative histopathology. The overall concordance of ultrasound TIRADS, Bethesda system and histopathology was 69.8%.

Conclusions: Higher TIRADS and Bethesda scoring among thyroid nodules was associated with increased risk of malignancy. Our study showed good concordance among US TIRADS, Bethesda system of cytology and final histopathology of thyroid nodules. US TIRADS was a good predictor of malignancy in indeterminate thyroid nodules.