Bosniak classification system: inter-observer and intra-observer agreement among experienced uroradiologists

The Bosniak classification is a diagnostic tool for the differentiation of cystic changes in the kidney. The process of categorizing renal cysts may be challenging, involving a series of decisions that may affect the final diagnosis and clinical outcome such as surgical management.

To investigate the inter- and intra-observer agreement among experienced uroradiologists when categorizing complex renal cysts according to the Bosniak classification.

The original categories of 100 cystic renal masses were chosen as "Gold Standard" (GS), established in consensus by two experienced uroradiologists. Three experienced uroradiological readers were blinded from the previous CT reports. Weighted κ was calculated to assess agreement, defined as: fair, 0.21-0.40; moderate, 0.41-0.60; good, 0.61-0.80; and very good, 0.81-1.00.

For readers the distribution of correctly classified lesions were as follows: BI, 95-100%; BII, 59-93%; BIIF, 54-92%; BIII, 58-95%; and B IV, 77-100% for the first review. Weighted κ for inter-observer/intra-observer variation was for Reader A: 0.85/0.99, Reader B: 0.97/0.99, and Reader C: 0.98/0.99, (P ≤ 0.001).

According to the calculated weighted κ all readers performed "very good" for both inter-observer and intra-observer variation. Most variation was seen in cysts catagorized as Bosniak II, IIF, and III. These results show that radiologists who evaluate complex renal cysts routinely may apply the Bosniak classification reproducibly.