Complex sentence: However, a publication by the American society of colon and rectal surgeons stated that internal rectal intussusception involved the mucosal and submucosal layers seperating from the underlying muscularis mucosa layer attachments, resulting in the separated portion of rectal lining "sliding" down.
Split into simpler sentences: However, a publication by the American society of colon and rectal surgeons stated that internal rectal intussusception was confined to the mucosal and submucosal layers of the rectal wall, and that there is a separation from the underlying muscularis mucosa layer attachments. This results in the separated portion of rectal lining "sliding" down.