Endocrine Abstracts

Objectives: Ultrasound-guided fine needle aspiration biopsy (FNAB) is a commonly performed diagnostic procedure for evaluation of thyroid nodules. The Bethesda System for Reporting Thyroid Cytopathology comprises six categories. Bethesda categories I and III present a challenge for deciding on further diagnostic and therapeutic procedures. Category I includes non-diagnostic or unsatisfactory results that may be due to both aspiration of cystic material from simple cysts or aspiration of too few thyroid cells to render a diagnosis. Category III includes atypia of undetermined significance or follicular lesions of undetermined significance. In the literature, the rate of Bethesda I ranges from 6.1% to 26.8%, while the rate of Bethesda III ranges from 3.7% to 27.4%. In these studies, 164 to 1399 specimens were included. The aim of our study was to evaluate the incidence of categories I and III in ultrasound-guided FNABs of thyroid nodules in the tertiary medical center with a very large number of thyroid patients.

Methods: Our retrospective study included 2167 specimens provided by ultrasound-guided FNAB. The selection of nodules for the FNAB was based on clinical findings, laboratory tests, thyroid scintigraphy with 99m-technetium-pertechnetate and ultrasound malignancy risk stratification according to the European Thyroid Association Guidelines. Simple cysts were excluded from the study. FNABs were performed by seven thyroid specialists from January 2019 to April 2021. For the procedure, 21-gauge and, rarely, 23-gauge needles were used. All ultrasound-guided FNABs were performed with an on-site cytologist, who used the aspirated material to immediately perform an air-dried smear. All cytology reports were performed by the same very experienced cytologist using the Bethesda System for Reporting Thyroid Cytopathology.

Results: Among the 2167 samples, there were 168 (7.7%) non-diagnostic or unsatisfactory (Bethesda I), 1750 (80.8%) benign (Bethesda II), 37 (1.7%) atypias of undetermined significance or follicular lesions of undetermined significance (Bethesda III), 119 (5.5%) follicular neoplasms or suspicious for a follicular neoplasm (Bethesda IV), 25 (1.2%) suspicious for malignancy (Bethesda V) and 68 (3.1%) malignant (Bethesda VI).

Conclusions: To the best of our knowledge, this study includes the largest number of ultrasound-guided FNAB specimens of thyroid nodules. When compared with the literature data, the incidence of Bethesda I and Bethesda III categories in our center is in the lower part of the reported range or lower, respectively. Most likely, this is due to the high frequency of FNABs in our center and the experienced cytologist who performs smears on site immediately after FNAB.