Mechanisms of mucous pool and retention cyst formation at the ureteroileal anastomosis site (UA) in failed ileal conduits

The use of ileal conduits for urinary diversion in patients with neurogenic bladder has fallen out of favour in recent times due to late complications of loop stricture, ureteric obstruction and reflux-related renal damage. Retrospective review of the Dept. of Histopathology files (ACH) was undertaken to investigate the sequence of, and possible mechanisms responsible for, histological changes present at the UA in surgically revised conduits. Material was available from 62 patients who had undergone loop revision over a 14 year period (1978-91). All cases showed variable villous atrophy, subepithelial inflammation and fibrosis. Striking findings in the 72 UAs that were available for assessment were the presence of epithelial lined cysts and cyst-containing polyps that protruded into the ureteric lumens, possibly contributing to obstruction. Closer study suggested that the initial changes were periglandular chronic inflammation, disorganisation of glands and extension of transitional epithelium over and into intestinal crypts. This was associated with occlusion and dilatation of glands. Larger cysts lined by intestinal, transitional or combined epithelium were found in 43 cases. Further enlargement of the cysts was associated with either rupture and formation of large subepithelial mucous pools (N=21, max.diam.=6.7mm), or with the formation of intraluminal polyps (N=9, max.diam.=2.5mm). This study demonstrates that overgrowth of ileal mucus-producing glands by transitional epithelium at UAs may be associated with glandular occlusion and dilatation, and with subsequent rupture and free mucus accumulation. Enlargement of epithelial lined cysts may also occur without rupture resulting in polyp formation. It is possible that these lesions may play a significant role in UA obstruction and therefore contribute to ileal conduit failure.