Background. Several reports have shown that majority of thyroid nodules are benign, but in 5 to 15% of cases, these lesions harbor malignancy. Though controversial, the prevalence of thyroid carcinoma appears to be associated with larger nodule size. Studies have shown that the diagnostic accuracy of fine needle aspiration biopsy is limited in large nodules.
Objective. To determine the diagnostic accuracy of Ultrasound Guided Fine Needle Aspiration Biopsy (USG-FNAB) smear in predicting malignancy in thyroid nodules 3cm in size or greater.
Methodology. Retrospective cohort study of patients whose nodules were subjected to USG-FNAB followed by thyroidectomy. Nodules were divided into two groups: study group consisted of nodules 3cm in size or greater; control group consisted of nodules less than 3cm in size. FNAB cytopathology was correlated with post thyroidectomy histopathologic diagnosis. Sensitivity, specificity, positive and negative predictive value, accuracy, and malignancy rate were computed and compared.
Results. Of the 363 nodules included, 123 measured 3cm in size or greater and 240 measured less than 3 cm in size. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy rate were 47.6%, 93.3%, 88.2%, 62.9%, 69.9% for the study group and 62.0%, 86.7%, 87.1%, 61.2%, 72.1% for the control group. Malignancy was observed in 51.2% of the study group and 59.2% of the control group. There was no statistically significant difference between the diagnostic accuracy (p>0.05) and malignancy rate (p=0.148) in both groups.
Conclusion. Increased nodule diameter is not associated with limitations in the diagnostic value of USG-FNAB nor is it correlated with an increased malignancy rate.
Key words. Thyroid neoplasm, accuracy, aspiration biopsy, fine needle