Characterization of afferent mechanisms in ileoanal pouches

The afferent innervation of ileoanal pouches plays an important role in perception and in reflex regulation of pouch function. We aimed to characterize afferent nerve function in ileoanal pouches and thereby explain the clinical presentation of patients with such pouches.

In eight patients who underwent surgery for active ulcerative colitis, perception of balloon distention of the pouch was measured using an electronic visceral distention device. In addition, pouch compliance and ileoanal reflex function were determined. Studies were performed during the initial stage of pouch creation (pouch without connection to proximal ileum, study 1) and a mean of 6.6 wk (range = 2-12 wk) after the second stage of the surgery (proximal ileum in continuity with the pouch, study 2). Nine normal volunteers made up the control group.

When expressed as intrapouch pressure, thresholds for stool and discomfort sensations were similar in patients with a pouch and controls. However, during ramp distention, patients with a pouch had a lower volume threshold for stool sensation (143 +/- 45 ml vs 300 +/- 30 ml, p = 0.009). The initial sensation of discomfort was experienced in the perineum at the S3 dermatome in all eight patients. At higher distention pressures, all patients with a pouch referred sensations to the abdomen, as opposed to only one of nine controls with such a referral pattern (p < 0.0001). Pouch compliance was markedly reduced during study 1 but normalized after continuity was established with the proximal ileum. Anal sphincter function in patients with a pouch was similar to that in controls.

Afferent pathways from both the ileum and rectum play a role in the mediation of sensations during mechanical distention of the ileoanal pouch and can explain a number of clinical features of patients with a pouch. The thresholds for activation of these pathways are not significantly altered by long-standing colorectal inflammation or by creation of the ileoanal pouch. Continuity with the proximal ileum significantly influences pouch compliance.