Abstract
Objective : To extract problems associated with the adoption of the thyroid Bethesda system for reporting thyroid cytopathology (BSRTC) in Japan, we analyzed atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS).
Study Design : We reviewed the aspiration cytology specimens of 10716 thyroid nodules.
Results : AUS/FLUS accounted for 2.2% of all nodules. Of these, 78.3% showed “focal features of papillary carcinoma in an otherwise predominantly benign-appearing sample” and “prominence of microfollicles with scant colloid in a sparsely cellular aspirate, insufficient for FN/SFN.” In 31.4% of the AUS/FLUS specimens, aspiration cytology was repeated, and 85% were categorized into benign or malignant lesions. In all, 39 nodules (16.5%) were resected within one year after the aspiration. All cases of “prominence of microfollicles with scant colloid in a sparsely cellular aspirate, insufficient for FN/SFN” were followed up without resection. The risk of malignancy was 13.1% in the AUS/FLUS nodules overall, and 79.5% in the resected ones.
Conclusion : According to the incidences of the risk of malignancy in the AUS/FLUS nodules overall, we think that adoption of the BSRTC is acceptable in Japan. However, as the risk of malignancy in the resected nodules was higher than that described in the BSRTC, recommended clinical managements and risk of malignancy different from those by the BSRTC must be proposed.
