Experimental study of neorectal physiology after formation of a transverse coloplasty pouch.

Abstract

A novel transverse coloplasty pouch (TCP) with a larger neorectal volume than a straight coloanal anastomosis (CAA) but a smaller volume than a short colonic J pouch (CJP) may improve short-term function after rectal excision. Twelve pigs were investigated 6 weeks after complete rectal excision followed by reconstruction with a CAA, CJP or TCP. The results were compared with findings in the normal pig rectum. The colonic transit times assessed by radio-opaque marker transit were 24 h for CAA, 60 h for CJP and 32 h for TCP. Non-operated control pigs had a mean transit time of 46 h. Pigs that had a CJP developed colonic dilatation and substantial faecal impaction. Colonic electrostimulation induced an adaptive relaxation in the normal rectum but a pressure increase in all neorecta, particularly after CAA. The neorectal longitudinal smooth muscle layer in pigs with a TCP was significantly thicker than that in pigs with a CAA or CJP; its thickness was closest to that of the normal pig rectum. Colonic smooth muscle layers 10 cm proximal to the coloanal anastomosis, above the neorecta, were significantly thicker after CJP than after CAA or TCP formation. No significant difference in microcirculation was observed between the three restorative procedures. Accelerated colonic transit and a lack of adequate relaxation upon endoluminal pressure increase was associated with urgency and incontinence after CAA. Delayed colonic transit, faecal impaction and ineffective muscular hypertrophy due to pouch dilatation and constipation indicated evacuation problems after CJP construction. Functional and morphometric data for TCPs suggested almost normal defaecation. Of the three restorative procedures, the data for TCPs were most similar to those obtained in the normal pig rectum at short-term follow-up.