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

Abstract

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.

Bethesda classification is a valuable guide for fine needle aspiration reports and highly predictive especially for diagnosing aggressive variants of papillary thyroid carcinoma

“…The percentage of ND nodules was lower in the post‐Bethesda period, but not significantly different from the pre‐Bethesda period ( P = 0.3) as shown by Koh et al . and Fazeli et al …”

The Bethesda System for Reporting Thyroid Cytopathology Explained for Practitioners: Frequently Asked Questions

“…Some malignant cases corresponded in the past to FV-PTC. This variant is characterized by a microfollicular structure and subtle nuclear changes in the sense of PTC, namely nuclear clearing and grooves, with few or no nuclear inclusions; these subtle nuclear changes can often pass unnoticed, leading to a FN/SFN diagnosis of these lesions (30,31). With the modification in the nomenclature and the introduction of NIFTP as a lesion of low malignant potential, fewer PTC cases will be found in the FN/SFN diagnostic category, thus reducing the lower end of the ROM of the FN/SFN DC (32,33).…”

Ultrasound-guided fine-needle aspiration cytology along with clinical and radiological features in predicting thyroid malignancy in nodules ≥1 cm

“…reported 19% (5/26) of FVPTC as benign on FNAC. [ 24 25 ] FVPTCs are known to be difficult to interpret on FNAC and tend to have more benign features, with patchy distribution of nuclear features. [ 25 26 27 ] Sparse cellularity, possible sampling error, and small sample size could also attribute to this high rate.…”