Purpose: Currently the relationship between bladder capacity and age in children with myelomeningocele is inadequately understood, such that nomograms derived from neurologically normal children are inappropriately applied to the myelodysplastic population. The aim of the present study was to evaluate age related bladder capacity and bladder capacity growth in children with myelomeningocele, and compare them to those of age matched, neurologically intact children. Materials and Methods: Bladder capacity was determined by cystometrography in children with myelodysplasia. Regression analysis was used to derive a relationship between bladder capacity and patient age. Data were stratified by sphincter activity, bladder sensation and uninhibited contractions, and regression analysis was repeated. To evaluate serial growth change in bladder capacity divided by time yielded a yearly bladder capacity growth rate in patients who underwent 2 cystometrograms done at least 3 months apart before age 9 years. Results: A total of 506 children satisfied study inclusion criteria. Bladder capacity (BC) was related to age for the first 9 years by the linear equation, BC = 24.5 (age) + 62. This equation is approximately 25% less steep than published age related bladder capacity in neurologically intact children using the formula, 32 (age) + 73. After data stratification bladder capacity in children with sphincter activity, bladder sensation or no uninhibited contractions approached that of neurologically intact children. In contrast, children without sphincter activity or bladder sensation, or with uninhibited contractions had markedly smaller age related bladder capacity. Bladder capacity growth in the subgroup of 55 children in whom 2 cystometrograms were performed at least 3 months apart before age 9 years confirmed a mean gain in capacity of 24 cc per year. Conclusions: Normal bladder capacity in children with myelodysplasia is approximately 25% less than in age matched, neurologically intact children. The bladder grows approximately 24 cc per year until age 9 years. When there is failure to store urine, bladder capacity is much smaller, while children with good storage features may attain the bladder capacity expected of age matched, neurologically intact children.
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