Besides radiotherapy, what can cause soft tissue thickening in peri rectal tissues?

Hemmorhoids: The most common reason to have thickening in the perirectal region would be hemorrhoids. These are swollen veins that sometimes develop clots in them. An infection in the peri-rectal region can cause swelling, such as herpes, warts, and bacterial infections. A perirectal abscess can also cause swelling and pain. If there is significant pain and swelling, you should be seen.