a segment of small intestine (ileum) used to convey urine from the ureters to the exterior into an appliance (see also urinary diversion). The ureters are implanted into an isolated segment of bowel, usually ileum but sometimes sigmoid colon, one end of which is brought through the abdominal wall to the skin surface. This end forms a spout, or stoma, which projects into a suitable urinary appliance. The ureters themselves cannot be used for this purpose as they tend to narrow and retract if brought through the skin. The operation is performed if the bladder has to be removed or bypassed; for example, because of cancer.
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