Most commonly occurs in infants aged between 3 and 12 months, with a peak at the age of approximately 9 months.
Presentation often includes colicky abdominal pain, flexing of the legs, fever, lethargy, and vomiting, with blood in the stool in some cases.
When there is clinical suspicion, imaging has a valuable role. Plain abdominal x-ray may reveal an intestinal obstruction and paucity of wind in the right lower quadrant. The presence or absence of free gas will influence subsequent management; abdominal ultrasound undertaken by an experienced radiologist will usually establish the diagnosis; contrast enema (most often air but may be liquid contrast) is the most specific and sensitive test for diagnosis. As well as being used therapeutically, it can also be used diagnostically where doubt remains.
The pathological location is typically ileocaecal.
Treatment involves reduction by contrast enema. Air is likely to be more effective and safer than liquid; in cases where this is unsuccessful or where peritonitis exits, surgery is required. Open reduction is then performed in uncomplicated cases, and intestinal resection for cases complicated by bowel necrosis and perforation.
Intussusception is a common cause of intestinal obstruction in young children and is defined as the prolapse of one part of intestine into the lumen of the adjoining distal part.  This condition most often occurs in the ileocaecal region. The lead point of the intussusception is most often an enlarged lymph node (Peyer’s patch) in the terminal ileum. Occasionally, the lead point is an anatomic abnormality of the intestine (a 'pathological lead point'). Conditions resulting in pathological lead points include luminal polyps, malignant tumours (including lymphoma), and benign mass lesions such as lipomata, Meckel's diverticulum, Henoch-Schonlein purpura, and enteric duplication cysts.   
This review will focus on idiopathic intussusception in infants. Intussusception in older children and adults is rare and is almost always caused by a pathological lead point.
Consultant Paediatric Surgeon
Leeds General Infirmary
JRS declares that he has no competing interests.
Dr Jonathan Sutcliffe would like to gratefully acknowledge Dr David Hackam, Dr Steven C. Gribar, and Dr Rahul J. Anand, the previous contributors to this topic. DH, SCG, and RJA declare that they have no competing interests.
Department of Pediatric Surgery
Cleveland Clinic Foundation
OS declares that he has no competing interests.
Emeritus Nuffield Professor of Paediatric Surgery
Institute of Child Health
London and Great Ormond Street Hospital NHS Trust
LS declares that he has no competing interests.
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