Defecation mechanisms after anterior resection with J-pouch-anal and side-to-end anastomosis in dogs

Colonic J-pouch-anal anastomosis or colonic side-to-end anastomosis is the reconstruction of choice after low anterior resection. However, the mechanisms of defecation after both reconstruction forms are still speculative.

Low anterior rectal resections were performed in 12 dogs with six colonic J-pouch-anal (pouch) and six coloanal side-to-end (SE) reconstructions. Four months postoperative stool frequency, intestinal transit time, and neorectal compliance were determined by radiography and barostat. Defecation mechanisms were evaluated radiographically during expulsion of artificial stool.

One dog with pouch reconstruction could not be evaluated due to an anastomotic leak, while the others had uncomplicated course. Spontaneous stool frequency was significantly increased with both reconstruction methods (control 2.0+/-0.9, pouch 2.7+/-1.2, SE 3.3+/-0.9 day; p<0.05). Intestinal transit time was significantly higher with pouch reconstruction due to storage of stool in the pouch and the descending colon compared to SE (control 760+/-82, pouch 592+/-97, SE 550+/-87 min; p<0.05). Compliance and functional capacity were higher in pouch than in side-to-end reconstructions (pouch 5.0+/-0.7 ml/mmHg, 124+/-23 ml; SE 2.7+/-0.3 ml/mmHg, 92+/-24 ml; p<0.05). During defecation, there were no contractions of the pouch detectable.

The colonic J-pouch reconstruction results in better functional outcome than side-to-end coloanal anastomosis. Our results show that pouch evacuation is passive and independent from pouch motility. The functional principle of the colonic J-pouch is not its reservoir function but a delay of colonic motility.