Not Only Length Matters! Impact of the Ileal Width on the Capacity of the Orthotopic Neobladder: The AADAPT Formula Tested on the Animal Model

Background: The capacity of a given shape of an orthotopic ileal neobladder (ONB) varies significantly, although the same length of preterminal ileum is utilised. Objective: To investigate the variability of the human ileal width and to create a mathematical formula that calculates its impact on the neobladder capacity. Design, setting, and participants: During 50 consecutive cases of robotic pelvic sur-gery, a segment of preterminal ileum was identified and the width was measured. A mathematical formula was created to calculate, for a given ileal length and width, the neobladder capacity and, for a given ileal width and neobladder capacity, the length of the (pre)terminal ileum to harvest. The accuracy of our model was tested on 28 pouches created by swine ileum. Outcome measurements and statistical analysis: The interindividual variability of the ileal width and its impact on the ileal neobladder capacity was investigated. Results and limitations: The mean hemicircumference of the human distal ileum is 2. 43 +/- 0.39 cm (range 2-3.5 cm). According to our geometric model and as confirmed in the swine model, an increase of 1 cm in ileal width increases the neobladder capacity by 85%. The Pearson correlation coefficient reported a strong positive rela-tionship between the formula-calculated and effective volumes of the pouch (r = 0.97). Moreover, for the same target capacity, 1 cm of difference in the ileal width implies harvesting 20 cm less ileum. A lack of testing on humans and appli-cation only to spheroidal neobladders are the main limits. Conclusions: The ileal width impacts the capacity of the ONB. For a given type of ONB, no standard length of ileum should be harvested; instead, the length should be tailored to the width of the ileum for a given patient. Clinical studies are required to confirm our model.