Bosniak classification of cystic renal masses version 2019 does not increase the interobserver agreement or the proportion of masses categorized into lower Bosniak classes for non-subspecialized readers on CT or MR.

PURPOSE: In a condition so prevalent as renal cysts, classifications should display satisfactory reproducibility not only among subspecialized readers. We aimed to compare the interobserver agreement of the Bosniak classification version 2019 (BC19) and current Bosniak classification (CBC) for non-subspecialized readers on CT and MRI and to verify whether BC19 leads to a downgrade of renal cystic masses when compared to CBC.
METHODS: We evaluated 50 renal cystic masses in 47 patients on MR and CT (25 per method). Eighteen readers (nine third-year radiology residents and nine abdominal imaging fellows) assessed the images using BC19 and CBC with an eight-week interval. Kappa statistic was used to assess agreement. An average score of Bosniak categories across all raters evaluated if there was downgrading of lesions on BC19.
RESULTS: The highest values of Kappa were found for fellows on CBC-MR (κ = 0.51), and the lowest values were found for residents on CBC-MR and fellows on BC19-MR (both κ = 0.36). On CBC, interobserver agreement was moderate for MR and CT (κ = 0.42 and 0.43, respectively), whereas on BC19, it was fair (κ = 0.38 and 0.40, respectively). The best agreements were in categories I (κ = 0.49-0.69) and IV (κ = 0.45-0.51). The poorest agreements occurred at IIF (κ = 0.18 on BC19-CT). There was a moderate median increase from CBC to BC19 in terms of Bosniak categories for both methods (MR [Z=-2.058, p = 0.040] and CT [Z=-2.509, p = 0.012]).
CONCLUSION: BC19, when compared to CBC, did not improve interobserver agreement nor diminished the proportion of masses categorized into lower Bosniak classes among non-subspecialized readers.