Bosniak classification of cystic renal masses: utility of contrastenhanced ultrasound using version 2019

To compare the latest 2019 version of Bosniak classification (BCnew) against Bosniak classification prior to 2019 (BCold) using contrast-enhanced ultrasound (CEUS) and to compare CEUS against contrast-enhanced CT (CECT) based on BCnew.

Patients who had both CEUS and CECT of the kidneys performed within three months of each other were included. CECT and CEUS images of renal cysts were retrospectively analysed by two independent readers using BCnew, extrapolating the BCnew criteria to CEUS. Where histopathology was not available, 3-year imaging follow-up was used as a reference standard.

Forty-nine patients with a total of 54 cysts were included. Using BCnew, Bosniak category between CEUS and CECT and both readers was concordant in 18 cysts (33.3%). Bosniak category between CEUS and CT was concordant in 27 cysts (50%) in reader 1 and in 33 cysts (61%) for reader 2. Based on Cohen's weighted kappa statistic (k), inter-observer agreement was moderate for CEUS (k=0.49) and fair for CECT (k=0.36). Agreement between CEUS and CECT for both readers was fair (reader 1, k=0.24; reader 2, k=0.37). Compared to using BCold, almost half of the benign cysts were assigned to a lower Bosniak category with CEUS using BCnew (reader 1, 42.6%; reader 2, 50%).

CEUS assessment based on BCnew more appropriately assigns benign renal cysts to a lower category than CEUS based on BCold. Readers tend to grade renal cysts to a higher Bosniak category with BCnew but with greater inter-reader agreement on CEUS than on CECT.