Pediatric cystogram: Are we considering age-adjusted bladder capacity?

There are a small number of reports in the literature describing bladder rupture during cystograms in children. We hypothesized that children undergoing cystograms may have their bladder overfilled during the test. We aimed to evaluate the current practice when performing cystograms in our institution, contrasting actual volume used to fill the bladder to the age-adjusted bladder capacity.

We performed a retrospective review of all voiding cystourethrograms(VCUG) and radionuclide cystograms (RNC) performed at the Children's Hospital of Eastern Ontario from 2006-2013. Formulas used to estimate age-adjusted bladder capacity: 1) infants <1 year: Capacity (mL) = (2.5 × age [months]) + 38 (Holmdahl et al, 1996); and 2) older children >1 year: Capacity (mL) = (2 + age [years]) × 30 (Koff et al, 1983).

A total of 2411 cystograms were done (1387 VCUG; 1024 RNC) in 817 infants and 1594 children older than one year - 1113 boys and 1298 girls. Generally, bladders tended to be overfilled with 32% more volume in mL than the expected age-adjusted bladder capacity - VCUG 151 (122) mL vs 120 (97) mL (p< 0.001) and RNC 191 (97) mL vs. 151(74) mL (p<0.001). Most importantly, infants had a striking overfilling rate of 64% and 38 % more volume than their expected age-adjusted bladder capacity for VCUG and RNC, respectively (p<0.001).

Bladders are filled above the estimated age-adjusted capacity in mL at the following rates: 32% in the whole group and 64% in infants undergoing VCUG. It raises concern of possible bladder rupture in this age group. Furthermore, this may lead to overgrading and overdiagnosing of vesicoureteric reflux, as well as overestimation of post-void residual. Attention should be paid to filling to age-adjusted bladder capacity and allowing the child adequate time to void during performance of the cystogram.