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

The Bethesda system for reporting thyroid cytopathology (TBSRTC) was developed in 2009 to standardize the terminology for interpreting fine-needle aspiration (FNA) specimens. 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. 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 %. The application of TBSRTC significantly improves diagnostic accuracy for indeterminate thyroid nodules, leading to higher rates of malignancy detection despite lower rates of thyroidectomies.