Here’s a diagram of what an intussuseption looks like:
These are not common! Part of the gut makes a circumferential inward U-turn, and the next section of gut slides inside. It’s a big deal, and causes blockages and worse. Since almost all of us have had our rectums removed (the rectum is not the anus), that’s not the affected part, but ileum could potentially protrude through the pouch inlet.