Background/Objectives: The 2023 revision of the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) simplified the subcategorization of category III into two groups: “AUS-nuclear” and “AUS-other”. The aim of this study was to investigate the risk of malignancy (ROM) of individual BSRTC categories with a particular emphasis on the “AUS-nuclear” and “AUS-other” subcategories and to check whether the low-risk follicular-cell-derived thyroid neoplasm (LRTN) interpretation or EU-TIRADS class of the nodule modify ROM. Methods: The analysis covered the FNA results of 18,225 nodules in 12,470 patients. The rate of malignancy (the upper limit of ROM) was established on the basis of the assessment of 1660 nodules treated surgically in 978 patients. Results: In the broadest variant, with all LRTNs regarded as malignant, the ROM for subsequent categories was as follows: I: 0.4–3.5%, II: 0.1–1.3%, III: 3.8–17.7%, IV: 23.3–27.8%, V: 79.6–90.1%, and VI: 86.3–100.0%. In AUS-nuclear nodules, the ROM was 10.5–28.9%, while in AUS-other nodules, it was 2.2–12.2%. The exclusion of NIFTP or all LRTNs from cancers mainly affected the ROM of AUS-nuclear nodules: 9.4–25.9% or 8.6–23.7%, respectively. EU-TIRADS 5 class increases the ROM in AUS-nuclear nodules to 78.3%, OR: 15.7 and in AUS-other to 40.7%, OR: 6.6. Conclusions: The 2023 BSRTC is a welcome step towards simplification of the way nodules are classified within category III. The AUS-nuclear subcategory is associated with a two-times-higher incidence of malignancy than the AUS-other regardless of LRTN interpretation and EU-TIRADS class of the nodule. The EU-TIRADS 5 class of the nodule is helpful in the identification of category III nodules with a high risk of malignancy.

Background/Objectives: The aim of the study was to compare the effectiveness of SWE in AUS-nuclear and AUS-other nodules, including nodules with an unequivocal cytology (UC), taking into account the size of the nodules. Methods: We evaluated 100 AUS-nuclear and 131 AUS-other nodules with known results of EU-TIRADS, repeat FNA (rFNA), and histopathological examination, and 92 nodules with UC: 47 malignant and 45 benign. Two SWE measures were used: Ewhole—capturing the largest possible area of the nodule; and Estiffest—limited to its hardest part. Results: In the UC group, values of both SWE measures above the thresholds were a significant malignancy risk feature regardless of the nodule size, but only Estiffest in nodules > 1 cm was an independent malignancy risk feature. In both AUS subcategories, similar results were obtained only for nodules > 1 cm; but, even in this group, rFNA and EU-TIRADS had a higher accuracy than SWE in the differentiation of benign and malignant nodules, and no SWE measures were an independent malignancy risk feature. However, in the AUS-nuclear subcategory, where PTC predominates among cancers, adding Estiffest to the EU-TIRADS and rFNA assessment led to some increase in sensitivity with an acceptable decrease in specificity. In the AUS-other subcategory, where the profile of cancers is more diverse, a similar effect was obtained by the addition of Ewhole. Conclusions: SWE may complement rFNA and TIRADS in category III nodules > 1 cm, but the decision whether to apply SWE and which measures should be used depends on the pre-test probability of cancer and the expected frequency of PTC among cancers.