An intussusception is an uncommon type of obstruction of the small or large intestine (gut) that usually occurs in children.
A polyp growing in the gut is picked up by the waves of muscular contraction that normally move food along. As the polyp moves down the gut it pulls the piece of gut it is attached to along with it, to cause an infolding of the gut into itself. This is an intussusception.
The child has obstruction of the gut, severe intermittent waves of pain, red jelly motions and paralysis of the intestine. The intussusception can be relieved by a barium enema (special x-ray) or colonoscopy (passing a flexible telescope in through the anus) if the large bowel is involved, but in the small intestine surgery is necessary. It is usually completely cured by appropriate treatment, but bowel perforation may rarely occur.