Migrating suture masquerading as a renal pelvic carcinoma: an unusual complication of the Kock pouch.

Following a radical cystectomy and the creation of a Kock pouch, a filling defect developed in the renal pelvis that appeared to be a transitional cell carcinoma. This appearance was produced by the retrograde migration and implantation of a fragment of suture material used in the creation of the pouch. It represents a previously undescribed complication of this procedure.