Intussusception is an acquired form of bowel obstruction in which one part of the bowel is drawn inside the lumen of adjacent distal bowel (Fig. 8.1). Compression of the vessels in the mesentery leads to lymphatic and venous obstruction with secondary oedema. The lumen of the intussuscepted bowel is occluded by the intussusceptum and leads to dilatation of proximal bowel and colic. The bowel at the commencement of the intussusceptum is called the lead-point. The common lead-points in intussusception are shown in Fig. 8.2. Pathological causes of intussusception account for only 10 % but include an inverted Meckel’s diverticulum, intestinal polyps or, ­occasionally, duplication cysts of the small bowel, lymphosarcoma or submucosal hae­morrhage with Henoch-Schönlein purpura. ‘Idiopathic intussusception’ is most likely to occur between 3 months and 2 years of age, whereas pathological lead-points present at any age (Fig. 8.3). One possible explanation why intussusception occurs most commonly between 4 and 7 months is shown in Table 8.2. The hyperplastic Peyer’s patch is propelled by peristalsis through the ileocaecal valve and drags the rest of the ileum with it.

When any infant presents with vomiting and general malaise, intussusception must be considered as a possible diagnosis. In fact, vomiting is the most frequent symptom of intussusception, since colic is not always recognized as such in some small infants. The reasons for this are shown in Table 8.3. Small infants are unable to interpret fully the subjective sensation, have an incompletely developed body image and lack speech. Therefore, recognition of the pain by the clinician depends on the reflex response it induces in the infant – this includes vomiting, pallor, sweating, screaming and pulling up the knees. In some, there appears to be no pain at all. In a typical situation, the colic is moderate to severe, lasts a minute or two and is followed by a pain-free interval of up to 10–20 min.