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. © Korean Society of Nuclear Medicine 2021.