The impact of bladder shape on the ultrasonographic measurement of bladder volume in children.

BACKGROUND

US is used for non-invasive assessment of bladder shape and for calculation of bladder volume.

OBJECTIVE

To evaluate the impact of bladder shape on the accuracy of US estimation of bladder volume in children and to calculate formulas for US estimation of volume for different bladder shapes.

MATERIALS AND METHODS

US was performed in 146 children (94 girls, 52 boys, age range 9 months to 17 years, median 7.9 years) referred for urodynamic investigation. Three bladder diameters were measured, and bladder shapes were categorized as round, ellipsoid, cuboid, triangular and undefined. Urine was collected, and total bladder volume calculated. Correction coefficients (k) were calculated for the whole sample and for each bladder shape using linear regression analysis.

RESULTS

Round bladder shape was present in 23%, 25% showed a cuboid shape, 21% an ellipsoid shape, 25% a triangular shape, and 6% had an undefined shape. Correction (regression) coefficient (k) for the whole sample was 0.66 (SE = 0.011); for round bladder 0.561 (SE = 0.013), cuboid bladder 0.923 (SE = 0.012), ellipsoid bladder 0.802 (SE = 0.006), triangular bladder 0.623 (SE = 0.007), and for undefined shape 0.749 (SE = 0.048). Mean percentage errors when using different correction coefficients were significantly lower than errors when using k = 0.5 applied to our data.

CONCLUSIONS

Bladder shape has considerable impact on the accuracy of US estimation of bladder volume in children. Correction coefficients should be used for volume measurements of different bladder shapes.