We investigated by ultrasonography the bladders of 30 young children (26 boys, 4 girls) without established bladder control immediately before voiding cystourethrography. The anterior/posterior (D), superior/inferior (H) and transverse dimension (W) of the bladder were determined. The small children had a significantly greater H value compared with D and W than older children in our previous study in 1993. The regression equation for DxHxW and actual bladder volume in 30 infants was calculated as y = 0.49 x + 3 (Eq. 1). When bladder volume of the 30 infants was estimated from DxHxW, the mean percentage error was much lower with Eq. 1 than with Eq. 2 (y = 0.68 x + 4), which had been determined for older children (mean +/- SD 16.8% +/- 10.7% vs. 44.7% +/- 26.2%) (P < 0.01). Thus, infants have a different bladder shape than older children and their bladder volume should be estimated using a specific formula designed for them.
