The Role of Tc-99 m-MIBI Scan in the Assessment of the Cystic Thyroid Nodule

Purpose A non-surgical therapeutic option requires assurance that a cystic thyroid nodule with non-diagnostic cytology is benign. This work was undertaken to determine whether Tc-99 m-MIBI scan (MIBI) findings can guide the best therapeutic option with confidence. Material and Methods We studied 81 cystic non-functioning thyroid nodules with non-diagnostic fine-needle aspiration biopsy (FNAB) report classified according to ATA 2015 ultrasonography (US) patterns for suspicion of malignancy. All had a MIBI to assess metabolic activity within the nodule as well as histopathological diagnosis. Diagnostic value analysis of MIBI as compared to the US pattern was determined. Results None of the 11 patients with US pattern of benign showed positive MIBI, and all had a histopathological report of benign. Diagnostic value of MIBI on US pattern of very low suspicion showed sensitivity, specificity, PPV, and NPV of 100%, 78.9%, 42.9%, and 100%, respectively. Conclusion Our data shows that the only approach to a safe non-surgical treatment option in a cystic nodule with non-diagnostic FNAB is when no metabolic activity is seen on MIBI.