The Implementation of the Bethesda System for Reporting Thyroid Cytopathology Improves Malignancy Detection Despite Lower Rate of Thyroidectomy in Indeterminate Nodules

Abstract

Background: The Bethesda system for reporting thyroid cytopathology (TBSRTC) was developed in 2009 to standardize the terminology for interpreting fine-needle aspiration (FNA) specimens.

Methods: A historical prospective case series design was employed. The study group included patients with a thyroid nodule classified as TBSRTC AUS/FLUS (B3) or FN/SFN (B4) in 2011-2012 in a tertiary university-affiliated medical center. Rates of surgery and malignancy detection were compared to our pre-TBSRTC (1999-2000) study.

Results: Of 3927 nodules aspirated, 575 (14.6%) were categorized as B3/B4. Complete data were available for 322. Thyroidectomy was performed in 123 (38.2%) cases: 66/250 (26.4%) B3 and 57/72 (79.2%) B4. Differentiated thyroid cancer was found in 66 (53.7%) patients: 30/66 (45.5%) B3 and 36/57 (63.2%) B4 (p=0.075). Operated patients were younger than the non-operated (B3: 52.4±16 vs. 59.7±13 years, p=0.009; B4: 51.7±15 vs. 60.5±14 years, p=0.042), and operated B3 nodules were larger than the non-operated (27.2 vs. 22.2 mm, p=0.014). Additional FNA was done in 160 patients (49.7%): 137/250 (54.8%) B3 and 23/72 (31.9%) B4 (p=0.002). The additional B3 nodules aspirations yielded a diagnosis of B2 in 84 patients (61.3%), B3 in 48 (35%), and B4 in 5 (3.6%). Of the 23 repeated B4 aspirations, B2 was reported in 5 (21.7%), B3 in 12 (52.2%), B4 in 4 (17.4%), and B6 in 2 (8.7%). The number of aspirated nodules was twice that reported in 1999-2000. The rate of indeterminate nodules increased from 6 to 14.6%, the surgery rate decreased from 52.3 to 38.2%, and the accuracy of malignancy diagnosis increased from 25.9 to 53.7%.

Conclusions: The application of TBSRTC significantly improves diagnostic accuracy for indeterminate thyroid nodules, leading to higher rates of malignancy detection despite lower rates of thyroidectomies.