It has been 20 years since the ileoanal pouch was first introduced into the array of options for the surgical treatment of ulcerative colitis and familial polyposis. Over these twenty years thousands of patients all over the world have had pouch surgery and are benefiting today by having avoided a permanent ileostomy. A question mark remains, however, over what will happen to the pouch as the patient, and his or her pouch, get older. Because the operation is relatively young, few patients have had their pouch for an extended period of time. As we approach the year 2000, it is appropriate to review what we know of what happens to the bowel that makes up the pouch, and to speculate a little about what we don't know.
The small intestine and the large intestine are very different, both in
structure and in function. The small intestine absorbs small nutrient
molecules from the liquid stool, whereas the function of the large bowel
is to absorb water and to store the stool until evacuation occurs. The
small bowel is long and narrow; the large bowel is short and wide. Stool
passes very quickly through the small bowel, transiting its
When we make a pouch we are changing the structure and function of the small intestine to make it work like a colon. It now stores stool and absorbs water. It comes as no surprise therefore to learn that as an ileal pouch gets older it starts to look like a colon.
Under the microscope the lining of the colon is flat. The small intestine normally has finger-like projections called villi that help with nutrient absorption. There are no villi in the colon. As pouches get older, researchers have found that they tend to lose their villi. The colon has a lot of mucus-producing cells (goblet cells), much more than the small bowel. Older pouches have increasing numbers of goblet cells. Older pouches also lose the look of small bowel and start to look like rectums. These changes usually take several years to start becoming apparent. What does this mean for the patient's state of health?
Our concern as physicians who care for patients with pouches is whether this tendency of small bowel pouches to become like large bowel will mean that there is a risk of cancer or "colitis" developing in the pouch. Indeed some preliminary reports suggest that in a few patients pre-cancerous changes can be found in the cells of a pouch. Polyposis patients are certainly prone to get polyps in their pouch but nobody has reported a cancer yet. As far as colitis is concerned, we already know about the syndrome of "pouchitis" that mimics colitis and can occur very early after pouch construction. This is different from a true return of colitis. There is as yet no sign of a return of true "colitis" in older pouches.
Because of the theoretical risk of "colon cancer" developing in an ileal pouch we recommend that patients come for yearly pouch checks. At this time biopsies will be taken to look for "dysplasia," an appearance of the cells lining the pouch that suggests that cancer may possibly develop. As time goes by and the number of patients with maturing pouches increases, the natural history of the elderly pouch will become more obvious. Stay tuned for more information.