Intussusception is a process in which a segment of intestine invaginates into the adjoining intestinal lumen, causing a bowel obstruction. Intussusception presents in 2 variants, ie, idiopathic intussusception, which usually starts at the ileocolic junction and affects infants and toddlers, and enteroenteral intussusception (jejunojejunal, jejunoileal, ileoileal), which occurs in older patients. The latter is associated with special medical situations (eg, Henoch-Schönlein purpura [HSP], cystic fibrosis, hematologic dyscrasias) and can occur in the postoperative period.

Two thirds of children with intussusception are younger than 1 year; most commonly, intussusception occurs in infants aged 5-10 months.There is a slight preponderance of males, with a male-to-female ratio of approximately 3:2.

The constellation of signs and symptoms of intussusception represents one of the most classic presentations of any pediatric illness; however, the classic triad of vomiting, abdominal pain, and passage of blood per rectum occurs in only one third of patients. The patient is usually an infant who presents with vomiting, abdominal pain, passage of blood and mucus, lethargy, and a palpable abdominal mass. These symptoms often are preceded by an upper respiratory infection.

Transverse  ultrasound shows a mass with a swirled appearance of alternating sonolucent and hyperechoic bowel wall of the loop-within-a-loop. Longitudinal ultrasound of the mass shows a submarine sandwich-like appearance of the intussuscipiens and the intussusceptum. There appear to be multiple layers, which represent the walls of the intussuscepted bowel loops.