Introduction: Thyroid Imaging Reporting And Data System (TIRADS) is helpful for risk stratification of thyroid nodules. However, there is a lack of data for TIRADS classification of different histological subtypes [classical papillary thyroid cancer (PTC), follicular variant of papillary thyroid cancer (FVPTC), and follicular thyroid cancer (FTC)], and benign thyroid nodules (follicular adenoma, oncocytic adenoma, and multinodular goiter (MNG)]. Methoxy-isobutyl-isonitrile (MIBI) imaging has a high negative predictive value for the exclusion of thyroid malignancy in hypofunctioning thyroid nodules. The aim of this analysis was to compare malignant and benign subtypes of thyroid nodule using three TIRADS and MIBI imaging.
Methods: Retrospective analysis of MIBI imaging studies. Hypofunctioning thyroid nodules were classified with Kwak-TIRADS, EU-TIRADS, and K-TIRADS. MIBI imaging was visually categorized.
Results: We included 242 thyroid nodules (32 malignant, 19 PTC, 7 FVPTC, and 6 FTC). When using Kwak-TIRADS 4C and 5 as a marker for high-risk nodules, we found 85.5% of the follicular adenoma, 80.8% of the MNG, 100% of the oncocytic adenoma, 100% of the FTC, 57.1% of the FVPTC, and 42.2% of the PTC to be below this cutoff. All PTC and FVPTC were MIBI-positive, 83% of the FTC, 78% of the follicular adenoma, 75% of the oncocytic adenoma, and 60% of the MNG were MIBI-positive.
Conclusion: TIRADS is useful to detect PTC, but FVPTC and FTC may be missed. MIBI imaging seems to be more suitable to detect FVPTC and FTC. However, neither TIRADS nor MIBI imaging are able to differentiate between follicular adenoma and FTC or FVPTC.