Simultaneous urodynamic and anorectal manometry studies in children: insights into the relationship between the lower gastrointestinal and lower urinary tracts.

BACKGROUND: Children with urinary incontinence (UI) have associated functional constipation (FC) and fecal incontinence (FI). The physiology between lower urinary tract (LUT) and anorectum in children has not been elucidated. AIMS: Observe the effect of rectal distention (RD) on LUT function, and bladder filling and voiding on anorectal function.
METHODS: Children with voiding dysfunction referred to Boston Children's Hospital were prospectively enrolled in combined urodynamic (UDS) and anorectal manometry (ARM). Anorectal and urodynamic parameters were simultaneously measured. Patients underwent two micturition cycles, first with rectal balloon deflated and second with it inflated (RD). Lower urinary tract and anorectal parameters were compared between cycles. KEY
RESULTS: Ten children (seven UI, four recurrent UTIs, nine FC ± FI) were enrolled. Postvoid residual (PVR) increased (p = 0.02) with RD. No differences were observed in percent of bladder filling to expected bladder capacity, sensation, and bladder compliance with and without RD. Bladder and abdominal pressures increased at voiding with RD (p < 0.05). Intra-anal pressures decreased at voiding (p < 0.05), at 25% (p = 0.03) and 50% (p = 0.06) of total volume of bladder filling. CONCLUSIONS & INFERENCES: The PVR volume increased with RD. Stool in the rectum does not alter filling cystometric capacity but decreases the bladder's ability to empty predisposing patients with fecal retention to UI and UTIs. Bladder and abdominal pressures increased during voiding, demonstrating a physiological correlate of voiding dysfunction. Intra-anal pressures decreased during bladder filling and voiding. This is the first time intra-anal relaxation during bladder filling and voiding has been described.