Intussusception is one of the most common surgical emergencies in childhood although many patients will present initially to paediatricians. Imaging has a major role both in the diagnosis and management of this condition. Intussusception occurs when a segment of bowel invaginates into an immediately adjacent segment, often likened to a telescope. The proximal, inner (inverting) segment of bowel is called the intussusceptum, and the outer distal (receiving) segment the intussuscipiens. The intussusceptum is propagated distally by bowel peristalsis leading to compression and angulation of the mesenteric vessels which causes reduced perfusion, venous congestion and bowel wall oedema, leading to ischaemia and eventually bowel necrosis. The physical presence of an intussusception also causes bowel obstruction, with colicky abdominal pain, distension and vomiting. Intussusception can occur at any age but is most common in the first two years of life, with its peak incidence between the ages of 3–9 months. It is often seasonal, occurring with increased frequency during late spring and autumn in the UK, rather than summer or winter.1

Four types of intussusception are described; ileo-colic, ileo-ileo-colic, colo-colic and small bowel intussusception (jejuno-jejunal and ileo-ileal). Ileo-colic intussusception is the most common type, accounting for over 80% of cases in children. In approximately 90% of these no underlying cause is found, although most probably arise as a result of hypertrophy of lymphoid tissue in Peyer’s patches or mesenteric lymph nodes following a recent infection acting as a “lead point” for intussusception to occur. A history of upper respiratory tract or gastrointestinal viral infection in the preceding week is often elicited. The terminal ileum is particularly rich in lymphoid tissue which explains why the ileocaecal region is so frequently involved. Even when there is evidence of lymphoid hyperplasia on imaging or at surgery, these types of intussusception are referred …