Cytological Diagnosis of Follicular Variant of Papillary Thyroid Carcinoma before and after the Bethesda System for Reporting Thyroid Cytopathology

Background: The follicular variant of papillary thyroid carcinoma (FVPTC) is the second most common subtype of papillary carcinoma after the classical variant. The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) has been introduced to standardize the practice of thyroid fine needle aspiration (FNA) reporting. We evaluated the impact of TBSRTC on the FNA interpretation of histologically proven FVPTCs. Method: Cytology reports of 455 histologically proven FVPTCs were reviewed. The rate of each TBSRTC category was compared between pre- and post-TBSRTC eras. Results: The distribution of FNA diagnoses for pre-TBSRTC cases included suspicious for follicular neoplasm (SFN; n = 51, 28.7%), papillary thyroid carcinoma (PTC; n = 47, 26.4%), suspicious for malignancy (SFM; n = 32, 18%), atypia of undetermined significance (AUS; n = 23, 13%), benign (n = 18, 10.1%), and nondiagnostic (ND; n = 7, 4%). Post-TBSRTC diagnoses were: AUS (n = 68, 24.6%), PTC (n = 64, 23.1%), SFM (n = 50, 18%), SFN and benign (n = 42, 15.2%) and ND (n = 11, 4%). SFN rate decreased significantly from 28.7 to 15.2% (p = 0.001) and AUS increased from 12.9 to 24.5% (p = 0.003). Conclusion: Following implementation of TBSRTC, the frequency of AUS diagnoses on FNA prior to surgical resection increased. Given that the rate of FVPTC diagnoses on thyroidectomy increased over the same period, this suggests that the use of AUS has resulted in greater surgical resection of FVPTC.