Is the impaired flow after hypospadias correction due to increased urethral stiffness?

Purpose: A low flow rate without clinical symptoms is commonly found in boys after hypospadias correction. Urethral calibration usually shows no abnormalities. We investigated whether this flow rate impairment might be caused by increased neo-urethral wall-stiffness. Methods: From Polyvinyl Alcohol cryogel two models of the urethra were made, a hypospadias model and a control model. Both models had a constant and equal inner diameter and equal compliance. The hypospadias model had a less compliant distal segment mimicking the distal neo-urethra after hypospadias correction. In both models flow rate was recorded as a function of bladder pressure. To test whether the length of the less compliant segment had an effect on the flow rate, both models were shortened by cutting off 1 cm segments. Results: In a physiological range of bladder pressures (10 - 130 cmH2O) the mean flow rate(± 1sem) in the hypospadias model was 2.8± 0.3 ml/s, significantly lower (p < .05) than in the control model (5.4 ± 0.6 ml/s). Shortening of the hypospadias model showed some increase in flow rate, however not statistically significant. In the control model there was also no significant variation in flow rate. Conclusion: We showed that a low compliant segment of a urethral model reduces the flow rate. Extrapolating these results to asymptomatic boys with a low urinary flow rate after hypospadias repair might justify a watchful waiting policy.

RePub contains a preprint of the article. See: http://www.intl.elsevierhealth.com/journals/jpur