The size of the colonic J-pouch is critical as regards the functional outcome. It has been suggested that construction of large colonic J-pouches (10-12 cm), as used at the beginning of the experience, can be the cause of evacuation disorders, characterised by incomplete evacuation or "split defecation" [25, 27, 29, 31, 33, 38, 48].
These problems in several series reach an incidence of 25%, as a probable consequence of the enlargement of the reservoir. Indeed, manometric and pouchographic studies have shown that the colonic pouch increases in size within one post-operative year ("baggy pouch") . The enlargement is substantially greater in a larger pouch and can be also associated to a horizontal inclination of the longitudinal axis ("floppy pouch"), as a consequence of an inadequate expelling force, so that efficient evacuation cannot be achieved .
Although evacuation difficulties are a potential drawback of pouch formation, the incidence can be reduced by constructing a smaller colonic J-pouch without offsetting the stool frequency or continence advantages. It is indeed demonstrated that a 5-cm pouch is as good as a 10-cm pouch in terms of functional outcome, avoiding the long-term problems in defecation of the larger reservoirs [44, 57-59].
This finding is noteworthy, as it confirms that pouch function is not a simple mathematical derivative of reservoir capacity.
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