what can possibly prolapse from anus?

A mucosal prolapse should be corrected permanently by removal of the mucosal lining. A full-thickness prolapse wouldn't be helped by removing the mucosa. How was the prolapse diagnosed?

An internal polyp?????  Just a guess.  Your surgeon will tell you for sure!  Best wishes.

A full prolapse was not seen on the Defography test, but it was mostly done in horizontal, not squatting position. I do not feel test was done correctly, but surgeon was certain after viewing pics that it was not a full prolapse. Said nothing he could do for me. Couple weeks later I had scope with new surgeon, already had consult scheduled with him, expecting full prolapse and he was surgeon I was referred to for pouch redo.  This surgeon also saw film and didn't think full prolapse but found flap during scope that had developed on anterior wall- so kind of partial prolapse, thus the mucousectomy and pouch advancement few weeks later. Interesting that you say full prolapse not correctable with Mucousectomy. I saw surgeon for post op and he says it must be the pouch (sm. Intestine) prolapsing though he wants me to wait it out. Said full prolapse usually protrudes  2-3 inches and mine is only protruding 1/2-1" right now. I don't know if it will get worse or how quickly but he said it's too early to consider pouch redo at this point, but may be necessary down the road. I will say that even though the prolapse makes each trip to bathroom a challenge, that the mucousectomy did reduce my frequency significantly. Down from 30-40 movements to 7-10. No longer taking Lomotil or Metamucil. Still struggling bit emptying but he said still swollen from surgery and could take 6 weeks to get 80% recovered. I'm way better physically and emotionally than one week ago! Thanks!

Good luck, LZJ! Time seems to be helping, which is excellent.