Progression, interobserver agreement, and malignancy rate in complex renal cysts ( ≥ Bosniak category IIF).

Objective: The objective of this study was to assess interobserver agreement, clinicopathologic correlation, and radiologic follow-up progression of complex cystic renal masses.

Patients And Methods: The medical records of 143 patients with 154 complex cystic renal masses were retrieved. Primary outcomes were interobserver agreement between the radiologists, and malignancy rates following surgical extirpation with or without follow-up in Bosniak IIF, III, and IV categories. Secondary outcomes were correlation between histology and degree of enhancement on contrast-enhanced computed tomography scans and survival analysis of patients with or without surgical intervention using the Kaplan-Meier analysis.

Results: The overall malignancy rate in patients who had surgery was 74.5% (29/39). Of 27 confirmed renal cell carcinoma on final histology, 9 were papillary renal cell carcinoma (incidence 33.3%). Assessment of interobserver agreement yielded a weighted kappa statistic value of 0.69 (95% confidence interval 0.56-0.82, P<0.0001). Radiologic progression rate of Bosniak IIF cysts over median follow-up of 18.5 months was 13% (10/78). There was no statistically significant difference between progression rate and regression rate of IIF cysts (13.8% vs. 11.5%) over the period of 24 months of follow-up. Most of the progression in complex cystic renal masses was seen in the first 2 years of follow-up. The malignancy rate on radiologic progression was 87.5% (8/9) and 75% (6/8) in Bosniak IIF and III cystic masses, respectively. The malignancy rate in Bosniak III cyst was 50% (4/8) without a period of initial observation or follow-up.

Conclusions: A good degree of agreement exists between radiologists in classifying complex renal masses. Malignancy rate is considerably high in Bosniak IIF when they exhibit radiologic progression on systematic follow-up.