**3. Basic principles of continent orthotopic urinary diversion**

In order to construct a functional orthotopic neobladder using intestinal segment, three basic principles must be satisfied.

First of all, the urethra of the patient must not be obstructed and must have adequate external sphincter mechanism.

Second, the reservoir must be sufficiently compliant to maintain a low pressure during the filling phase. This is best achieved by opening the bowel segment longitudinally to completely detubularize it and folding it to create a spheric shape.

The shape of the neobladder is of great importance. The sphere seems to be the best choice as it has the greatest internal volume and therefore the greatest capacity.

In addition, the Kock pouch and also S and W shaped reservoirs maintain low internal pressures throughout the filling phase, due to low pressure contractions of the bowel wall.

All current continent diversion techniques use detubularized bowel to construct the reservoir.

Third, the reservoir must have adequate volume to allow for reasonable voiding intervals. In general, this should be at least 300 to 500 mL once the pouch is mature.

The standard 44-cm length of ileum formed into a double-folding reservoir by the Kock technique (also used for both the Studer and T pouch neobladders) has an initial capacity of less than 200 mL but within the first year stretches to hold 500 to 600 mL at low pressure [1].

In general, small bowel, when available, has advantages over colon in terms of wall compliance and ability to stretch, as well as reduced mucous formation.
