The Bethesda system for reporting thyroid fine needle aspiration cytology: a study comparing the results of two centers from two different countries.

Three thousand and forty-one cases of thyroid FNAs have been classified following the Bethesda system for reporting thyroid cytopathology. They have been collected over a two-year period in two different university centers; one in Turkey and the other in France. Harmonization in the distribution of the diagnostic categories as well as an increasing risk of malignancy towards “benign” to “malignant” categories were shown in both of the series and were quite equivalent to the Bethesda system expected results. Furthermore, applying this terminology gives us the opportunity to make an easy comparison between our results. However, some discrepancies still exist between these two compared series for the estimated risk of malignancy per category. One reason could be the differences in application of the cytological criteria. However, close analysis of our results and comparison with already published series, lead us to point out that differences between countries and institutions could also be due to factors other than the Bethesda terminology such as epidemiological factors, organized national screening and interobserver variability in histopathology.