Natural history and etiology of high pressure voiding in male infants.

PURPOSE: We sought to determine the etiology of high pressure voiding in male infants, and to clarify the mechanisms of its improvement with maturation. MATERIALS AND METHODS: We retrospectively reviewed 106 videourodynamic studies obtained from 78 male infants with either congenital renal abnormalities or episodes of urinary tract infection, without any neurological disorders or lower urinary tract symptoms. We evaluated the relationship between age, bladder capacity and maximum voiding detrusor pressure. To evaluate voiding patterns more precisely fluoroscopic images of the lower urinary tract were continuously recorded in 64 voiding phases. RESULTS: Maximum voiding detrusor pressure showed a significant negative correlation with age as well as bladder capacity. Sharply increased detrusor pressure was noted, as were increased sphincter electromyographic activity, dilated posterior urethra and interruption of urinary stream associated with intermittent closure of the membranous urethra. Sufficient relaxation of the external sphincter was observed in all cases. True maximum voiding detrusor pressure also exhibited a significant negative correlation with age. Interruption of urine stream was commonly observed (92% of patients). Neither mean number nor duration of urine stream interruptions changed with age. The increase in detrusor pressure in response to sphincter contractions revealed a significant negative correlation with age. CONCLUSIONS: High voiding pressure in male infants results from detrusor-sphincter dyscoordination and detrusor hypercontractility in response to the dyscoordination. Its improvement with maturation is mainly due to resolution of detrusor hypercontractility.