Prevalence of Malignancy and Histopathological Association of Bosniak Classification, Version 2019 Class III and IV Cystic Renal Masses

Abstract

Bosniak Classification, version 2019 (v2019) describes 2 types of class III and IV masses each: 1) thick, wall/septa ≥4 mm (III-WS), 2) obtuse protrusion ≤3 mm (III-OP), 3) obtuse protrusion ≥4 mm (IV-OP), and 4) acute protrusion of any size (IV-AP). The purposes of this study were to determine the prevalence of malignancy and histopathological features of class III and IV masses and subclasses. In this institutional review board-approved and Health Insurance Portability and Accountability Act-compliant study, 3 fellowship-trained abdominal radiologists (R1-3) reviewed cystic renal masses that had tissue pathology and preoperative renal mass protocol computerized tomography or magnetic resonance imaging. Classes based on v2019 and prior classification systems were retrospectively re-assigned and associated with malignancy, aggressive histologic features (necrosis or high Fuhrman grade) and radiological progression following resection. The final sample included 79 masses (59 malignant, 20 benign) from 74 patients. Based on v2019, prevalence of malignancy ranged from 56% to 61% (mean 60%) for class III and 83% to 83% (mean 83%) for class IV (p=0.036, 0.013, 0.036 for 3 fellowship-trained abdominal radiologists). Prevalence of malignancy within subclasses were: III-WS (overall 49%; range 47%-53%); III-OP (76%; 71%-85%); IV-OP (78%; 75%-87%); IV-AP (87%; 82%-95%; p=0.029, 0.001, 0.005). All readers were more likely to classify malignancies with aggressive histologic features as class IV (88% to 100%) rather than class III (0% to 12%; p=0.012, <0.001, 0.002), corresponding to a negative predictive value of 96% to 100%. After treatment (mean followup length 1,210 days), 1 patient developed metastases. Bosniak Classification, version 2019 can help risk stratification of class III-IV masses by identifying those likely to be malignant and have aggressive histologic features.