Comparison of rectus abdominis muscle and musculoperitoneal flap in closure of urinary bladder defects in a rat model

To study the histological differences between a muscle flap and a musculoperitoneal flap used as a urinary bladder wall substitute, we prospectively studied these flaps in 24 Wistar albino rats. In 12 rats a rectus abdominis muscle flap including the overlying peritoneum (RAMP flap) was sutured into a surgical defect of the bladder wall. The rectus abdominis muscle flap was interposed without peritoneum (RAM flap) in the other 12 rats. The animals were killed on postoperative day 6 (6 RAMP flaps and 6 RAM flaps) and day 90 (5 RAMP flaps and 5 RAM flaps) to obtain early and late histological results. The 2 remaining rats (1 RAMP flap and 1 RAM flap) died before 90 days. Partial resurfacing of the flaps muscle surface with urothelium was observed on the sixth postoperative day in both the RAMP and the RAM group. At that time, no significant histological difference in the urothelium was observed between the RAMP and the RAM flaps. After 90 days, resurfacing with urothelium was complete in both groups. We concluded that a urothelium or peritoneum lining is not needed to protect a muscle flap against contact with urine. Histologically, the presence of peritoneum in the early postoperative period seems to have had a positive effect on the quality of neo-urothelium.