[Sonographic volumetry of the urinary bladder in paediatric patients. value of different calculation formulae taking into account a simple formula that is calculable in one's head].

BACKGROUND: Volumetry of the unrinary bladder is a frequently performed sonographic procedure. Usually the formula of the prolate ellipsoid is -applied for this purpose. In the literature however a variety of different formulas is proposed. PURPOSE: The aim of this study was to evaluate different simple formulae used for the calculation of the bladder volume in children, taking into account a formula that is easily calculable in one’s head. MATERIAL AND METHODS: 139 children were exam-ined by sonography, 6 different formulae were -applied. The bladder volume was confirmed by micturition. Only children without residual volume were included in the study. RESULTS: 82 children (mean age: 8.5 years) could be included with a mean bladder volume of 92 mL (0 to 227 mL). The mean error ranged from 20.2 % (cuboid formula) to 38.0 % (prolate ellip-soid). With decreasing bladder volume all for-mulae showed an increasing error and a tendency for underestimation of the bladder volume. For small volumes best results were achieved by the cuboid formula with a mean error of 26.4 %. The formula of the prolate ellipsoid yielded the worst results. The proposed truncation-formula, easily calculable in one’s head, showed better results than both the formula of the prolate ellipsoid and the cuboid formula. CONCLUSION: The formula of the prolate ellipsoid should not be used for bladder volumetry in children. Small bladder volumes should be calculated by multiplying the three diameters of the bladder (cuboid formula). If the calculated vol-ume lies above 60 mL a correction factor of 0.8 should be used to avoid overestimation of the true bladder volume.