Intussusception is the invagination of a segment of intestine into the adjacent distal bowel. The invaginating segment is referred to as the intussusceptum, and the distal bowel, which receives the intussusceptum, is the intussuscipiens. It is the most common cause of intestinal obstruction in infants and young children 6 to 36 months of age and the most common abdominal emergency in early childhood. More than 50% of affected children present before 1 year of age, and 80% of cases occur before 2 years. Intussusception is rare before 9 weeks of age, but the incidence increases until about 6 to 7 months of age, where it occurs in about 60 per 100,000 infants. By 1 year of age, the rate is about half of this. Rates are higher among African American and Hispanic infants than among Caucasians. There is a 3:2 male predominance.

Ninety percent of cases are idiopathic, and the remaining 10% are associated with an underlying cause that produces a lead point.¹ Cases associated with pathologic causes producing a lead point include Meckel’s diverticulum, intestinal polyps, intestinal lymphoma, duplication cysts, Henoch–Schönlein purpura, cystic fibrosis, and benign hamartomas, and are much more common in children older than 5 years of age. Intussusception in children younger than 3 months is uncommon but is also highly associated with a pathologic lead point.² After the age of 3 years, the incidence of a pathologic lead point increases with Meckel’s diverticulum, lymphoma, and polyps as the three most commonly found.¹ Patients with Burkett’s lymphoma as a lead point usually present at an older age (median 10 years) and are almost always ileocolic in location.³ Patients with intussusception caused by pathologic lead points generally fail radiographic reduction and require surgical reduction with resection of the underlying pathology.

In idiopathic cases, the presumed pathogenesis is a preceding viral infection that produces lymphoid hyperplasia in Peyer’s patches in the terminal ileum. A strong association with preceding adenovirus infection has been reported.^4–6 The lymphoid hyperplasia is thought to act as the lead point. Ileocolic intussusception is most common, but ileoileocolic, jejunoileal, or colocolic intussusception may also occur.

When the intussusceptum enters the intussuscipiens, its attached mesentery, blood supply, and lymphatic drainage are compromised. The invaginated portion of the intestine develops edema and venous congestion resulting in tissue ischemia. Luminal obstruction also occurs as a result of the intestinal invagination, which increases wall tension and worsens tissue compromise. If not recognized and treated, it may proceed on to ischemia, bowel necrosis, perforation, and peritonitis.¹

Children classically present with sudden onset of intermittent, severe, crampy abdominal pain, inconsolable crying, and vomiting which may become bilious. Initially, the child may appear comfortable and act well between episodes, but if the intussusception is not reduced, dehydration and lethargy develop. Irritability interspersed with periods of quiet resting should prompt one to consider intussusception. In infants younger than 1 year of age, lethargy may predominate early in the symptom course and may be associated with miosis and pallor.^7,8 This altered sensorium with intussusception may be seen after prolonged symptoms or during the early stages. Mental status changes may be accompanied by pronounced pallor, mimicking shock. A transient response to naloxone was documented in one case.⁸ In children younger than 12 months, the strongest clinical predictors are emesis, irritability, and blood in the stool.⁹

On inspection, the abdomen may appear normally soft or may be mildly distended, and the right lower quadrant may seem empty (Dance’s sign). Guarding is uncommon and should raise concern for the presence of bowel compromise. Bowel sounds may be normal, decreased, or absent. A sausage-shaped mass may be found. The advancing mass, typically ill-defined and variably tender, is most commonly palpable in the right upper quadrant or mid-abdomen, but may be palpated in any quadrant or on rectal examination. Many children have gross or occult blood in the stool on rectal examination, although grossly bloody bowel movements and “currant jelly stools” are late findings. Currant jelly stools, which are bloody, maroon-colored, and mucous-laden, are a result of mucous production and mucosal sloughing from vascular compromise. The classic triad of pain, a palpable sausage-shaped abdominal mass, and currant jelly stool is seen in fewer than 15% of cases.