Complex renal cysts (Bosniak ≥IIF): interobserver agreement, progression and malignancy rates

Objective The objective was to assess the interobserver agreement rate, progression rates and malignancy rates in the assessment of complex renal cysts (>= Bosniak IIF) using a population-based database. Methods A regional database identified 452 complex renal cysts in 415 patients between 2009 and 2019. Each patient was tracked and followed up using a unique identifier and deterministic linkage methodology. The interobserver agreement rate between radiologists was calculated using a weighted kappa statistic. Progression and malignancy rates of cysts (Bosniak >= IIF) over the 11-year period were calculated. Results The linear-weighted kappa value was 0.69 for all complex cysts. The rate of progression and regression of Bosniak IIF cysts was 4.6% (7/151) and 3.3% (5/151), respectively. All malignant IIF cysts progressed within 16 months of diagnosis. The malignancy rate of surgically resected Bosniak III and IV cysts was 79.3% (23/29) and 84.5% (39/46), respectively. Of all malignant tumours, 73.8% and 93.7% were of low ISUP grade and low stage, respectively. Conclusions This study further confirms that there is a good degree of agreement between radiologists in classifying complex renal masses using the Bosniak classification. The progression rate of Bosniak IIF cysts is low, but the malignancy rates of surgically resected Bosniak IIF, III and IV cysts are high. Benign cysts are frequently resected, and a very high proportion of histopathologically confirmed cancers in complex renal cysts are of low grade and stage.

Automated summary

This study confirmed a good degree of agreement between radiologists in classifying complex renal masses using the Bosniak classification, with low progression rates of Bosniak IIF cysts but high malignancy rates of surgically resected cysts. Benign cysts were frequently resected, and the majority of histopathologically confirmed cancers in complex renal cysts were of low grade and stage.