AUA 2018: Long-Term Active Surveillance of Complex Cystic Renal Masses & the Heterogeneity of BOSNIAK 3 Lesions

San Francisco, CA ( The authors presented a study attempting to better characterize the frequency of Bosniak cyst class changes and determine the average growth rate of cysts, helping to validate the safety of active surveillance. Consecutive patients referred for management of complex cysts (>= Boniak 2f) at a single institution between January 1, 2003 - Aug 31, 2014 were included in the analysis. Patients required at least 6 months of diagnostic imaging follow-up until the patient was discharged, deceased, underwent surgery or was lost to follow-up. Patients were excluded if they had greater than 2 complex cysts, immediately underwent surgery, or had pre-existing renal disorders. All imaging studies (CT, MRI, ultrasound) were re-evaluated and any stage change was reviewed with a blinded radiologist. Bosniak class and cyst size were only obtained from the CT or MRI. The Bosniak classification was sub-refined by separating septated enhancing Bosniak cysts (3s) and Bosniak 3 cysts with cyst wall only nodularity (3n) (Figure 1). Multivariable (MV) logistic regression was performed to identify predictors of Bosniak classification change. Kaplan-Meier (KM) curves were used to analyze Bosniak cyst progression or regression. 

Figure 1 – Bosniak subclassification:
Figure 1 Bosniak subclassification

A total of 1640 images were reviewed in a total of 140 patients. Overall 140 lesions identified in 106 patients were analyzed. Of the remaining 1011 images there were 464 CT scans and 408 MRIs. Median follow-up for all patients was 46 months [IQR 23, 65.5] and patients underwent a median number of 7 [IQR 4,9] diagnostic scans. On MV analysis progression was determined by cysts that were nodular (HR 6.16 [2.58,14.72], p<0.00004). Cysts that were entirely endophytic were less likely to progress HR 0.21 [0.05,0.85], p=0.028). On KM analysis Bosniak 3s cysts were more likely to regress (p=0.0178) while Bosniak 3n cysts were more likely to progress than 3s cysts (p=0.0002) (Figure 2). The growth rate of 3n was 0.19cm/year (p=0.0493) and 2f cysts was 0.11cm/year (p=0.0327). There was no significant difference in growth rate between Bosniak 4 and non-Bosniak 4 lesions. None of the patients developed metastatic disease.

Figure 2 – Kaplan -Meier graphs of regression and progression:
Figure 2 Kaplan Meier graphs of regression and progression

The limitations of the study included the fact that this was a single institution experience, the volume of nodularity and septations was not measured, the imaging was not standardized over the entire study period, and there was no usage of contrast-enhanced US.

In conclusion, classification of Bosniak 3 cysts into 3n and 3s better characterizes their clinical behavior. Diagnostic change among Bosniak 3s and 2f cysts is common; Bosniak 3n cysts behave more like Bosniak 4s. Most complex kidney cysts can be safely monitored without intervention, diagnostic change is frequent, and interval imaging between studies should be increased.

Presented by: Deepak Pruthi, MD, San Antonio, TX, USA

Written by:  Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre @GoldbergHanan at the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA