Definition: a part of an intestine or its adjacent mesenteric sheath, such as an adjacent intestine. Age of onset: Infants under 2 years old, especially 4 ~10 months old, mostly occur in obese infants with good nutrition, and there are more males than females in clinic.

Etiology: the cause of intussusception is unknown, and it can be divided into primary and secondary according to the cause.

Primary: due to the irregular peristalsis of the intestine and the persistent local spasm of the annular muscle. Inducing factors: enteritis, diarrhea, high fever and dietary changes lead to intestinal dysfunction.

◆ Secondary: secondary to intestinal canal, such as some organic lesion or congenital malformation in intestinal cavity, intestinal polyp, tumor, allergic purpura, Meckel's diverticulum inversion and appendix stump inversion.