Bladder capacity and growth in classic bladder exstrophy: A novel predictive tool

Abstract

Introduction: Bladder capacity (BC) is an important metric in the management of patients with classic bladder exstrophy (CBE). BC is frequently used to determine eligibility for surgical continence procedures, such as bladder neck reconstruction (BNR), and is associated with the likelihood of achieving urinary continence.

Objective: To use readily available parameters to develop a nomogram that could be used by patients and pediatric urologists to predict BC in patients with CBE.

Study design: An institutional database of CBE patients was reviewed for those who have undergone annual gravity cystogram 6 months after bladder closure. Candidate clinical predictors were used to model BC. Linear mixed effects models with random intercept and slope were used to construct models predicting log transformed BC and were compared with adjusted R², Akaike Information Criterion (AIC), and cross-validated mean square error (MSE). Final model evaluated via K-fold cross-validation. Analyses were performed using R version 3.5.3 and the prediction tool was developed with ShinyR.

Results: In total, 369 patients (107 female, 262 male) with CBE had at least one BC measurement after bladder closure. Patients had a median of 3 annual measurements (range 1-10). The final nomogram includes outcome of primary closure, sex, log-transformed age at successful closure, time from successful closure, and interaction between outcome of primary closure and log-transformed age at successful closure as the fixed effects with random effect for patient and random slope for time since successful closure (Extended Summary).

Discussion: Using readily accessible patient and disease related information, the bladder capacity nomogram in this study provides a more accurate prediction of bladder capacity ahead of continence procedures when compared to the age-based Koff equation estimates. A multi-center study using this web-based CBE bladder growth nomogram (https://exstrophybladdergrowth.shinyapps.io/be_app/) will be needed for widespread application.

Conclusion: Bladder capacity in those with CBE, while known to be influenced by a broad swath of intrinsic and extrinsic factors, may be modeled by the sex, outcome of primary bladder closure, age at successful bladder closure and age at evaluation.

Keywords: Bladder capacity; Classic bladder exstrophy; Growth model.