What is intussusception and who gets it?
Intussusception is a condition in which part of the intestine folds into the section next to it. The segment that telescopes in is the intussusceptum; the segment that receives it is the intussuscipiens. Almost all cases have the intussusceptum proximal to the intussuscipiens, because peristalsis pulls the proximal bowel into the distal bowel (StatPearls). In most infants it is the ileum passing through the ileocaecal valve into the caecum (ileocolic type).
As the bowel telescopes it drags its mesentery and blood supply with it. Venous obstruction causes oedema, then arterial compromise causes ischaemia, mucosal sloughing, necrosis and perforation if the segment is not relieved. Untreated, it can be fatal within two to five days (StatPearls).
| Point | Detail |
|---|---|
| Usual age | 6 to 18 months; peak 4 to 9 months (StatPearls). A global review found peak incidence at 4 to 7 months and lowest incidence at 0 to 2 months |
| Sex | Boys more than girls, about 3:1 (StatPearls) |
| Commonest site | Ileocolic - ileum into caecum |
| Cause | About 90% are idiopathic with no anatomical lead point; a lead point is found in roughly 10% (StatPearls) |
| Adults | About 1% of adult bowel obstructions, and usually linked to a neoplasm or other organic lead point |
What causes intussusception and what are the lead points?
In idiopathic (primary) intussusception there is no pathological lead point, but the distal ileum shows hypertrophied Peyer patches and enlarged mesenteric nodes, typically after gastroenteritis or an upper respiratory infection. History of a respiratory or flu-like illness is present in about one-third of children. The strongest viral association in one population-based study was adenovirus species C.
| Lead point | Notes |
|---|---|
| Meckel diverticulum | The classic structural lead point; may also bleed |
| Polyps | Includes polyps in Peutz-Jeghers syndrome |
| Intestinal duplication / enteric cyst | Congenital lesion pulled in by peristalsis |
| Appendix stump or appendicitis | Inverted stump acts as the lead |
| Lymphoma / other malignancy | More likely in older children and adults |
| Henoch-Schonlein purpura | Submucosal haematoma in the bowel wall can lead the telescope |
| Cystic fibrosis | Inspissated meconium or faecal masses |
| Worm infestation | Reported as a lead point |
| Post-operative | Rare complication after laparotomy - up to 0.25% in children (retroperitoneal tumour resection, Ladd procedure, diaphragmatic surgery, pancreatectomy) |
What is the classic presentation of intussusception?
A previously well infant has sudden intermittent, colicky abdominal pain: bouts of crying with the knees drawn up to the chest, with the child normal or lethargic in between. The pain is intermittent because the trapped segment transiently stops contracting. Vomiting follows, at first of recent feeds and later bilious.
- Red currant jelly stool - ischaemic mucosa sloughs and mixes with blood and mucus. It appears late, may follow within about 12 hours of onset in some, and occurs only in a minority of cases.
- Sausage-shaped abdominal mass on palpation.
- Dance sign - retraction of the right lower quadrant on examination.
- Rectal examination - blood on the finger; occasionally the intussusceptum can be felt.
- Lethargy and pallor - the quiet, floppy infant between bouts.
- Late signs - dehydration, shock, fever, anal protrusion of the intussusceptum, peritonitis from necrosis or perforation.
Intussusception can also complicate Henoch-Schonlein purpura; a child with HSP rash and severe abdominal pain should have it excluded. See also vasculitis classification.
How is intussusception diagnosed - target sign and pseudokidney sign?
Ultrasound is the investigation of choice in children. Reported sensitivity is about 98% and specificity about 98% in high-quality series, though it is operator-dependent. It also shows blood flow on Doppler, a lead point and trapped fluid between the loops.
| Sign | Modality / view | What it represents |
|---|---|---|
| Target (doughnut) sign, about 3 cm across | Ultrasound or CT, transverse view | Hypoechoic outer oedematous bowel wall around a hyperechoic core of bowel and mesenteric fat |
| Pseudokidney sign | Ultrasound, longitudinal view | Same mass seen lengthways; resembles a kidney |
| Sandwich sign | Ultrasound, longitudinal | Layered appearance of the telescoped bowel |
| Meniscus sign | Contrast enema | Rounded apex of the intussusceptum protruding into the contrast column |
| Coiled-spring sign | Contrast enema | Contrast outlining oedematous mucosal folds of the returning limb |
| Trapped-fluid sign | Ultrasound | Fluid between serosal surfaces; linked to lower reduction rates |
A plain abdominal X-ray is not diagnostic but can show obstruction or perforation (free air), which affects whether enema reduction is safe. CT is used when ultrasound is doubtful and is the preferred test in adults, but in young children it may need anaesthesia and carries radiation and contrast risks.
How is intussusception treated - enema reduction or surgery?
After resuscitation (fluids and electrolyte correction), a stable child without peritonitis goes for non-operative reduction by enema under imaging guidance. Barium, water-soluble contrast, saline or air can all be used, and the enema both confirms the diagnosis and treats it. Success is over 80%; up to 10% recur within 24 hours (StatPearls).
| Option | When | Key points |
|---|---|---|
| Pneumatic (air) enema | Stable child, no contraindication | Controlled insufflation under fluoroscopy or ultrasound with a manometer. A 2025 meta-analysis of 29 studies found higher success than liquid enema and shorter reduction time, with no difference in perforation or recurrence |
| Hydrostatic (saline / contrast) enema | As above | Fluid column about 100 cm above the patient (may be raised to 150 cm). Ultrasound-guided saline avoids radiation. Historic rule of 3: 3 attempts, 3 minutes each, 3 feet height |
| Delayed repeat enema | Partial reduction, child stable | Improves reduction rates; recurrence can be re-managed non-operatively up to about three times |
| Surgery | Peritonitis, perforation, non-responsive shock or failed enema | Manual reduction by manual squeezing of the telescoped bowel; resection if bowel non-viable or lead point; laparoscopy possible |
Adjuncts: StatPearls notes dexamethasone has shown promising results to improve enema success, while evidence for glucagon was lacking. In adults, enema is not used because a lead point or organic lesion is usual; they need CT and surgical resection.
What are the complications and the differential diagnosis?
Delay is dangerous: the longer the segment is trapped without blood supply, the less effective non-surgical reduction becomes and the more likely resection is. Complications include bowel necrosis, perforation, peritonitis, sepsis and, rarely, short bowel syndrome. Most children reduced early do well.
| Condition | Distinguishing feature |
|---|---|
| Acute gastroenteritis | Pain, vomiting and stool with blood and mucus can overlap, but diarrhoea is the leading symptom |
| Rectal prolapse | Mucosa continuous with perianal skin; in intussusception the finger passes indefinitely into the sulcus around the protrusion |
| Meckel diverticulum bleed | Painless red or maroon rectal bleeding; may also be the lead point |
| Appendicitis | Constant localising pain, fever and tenderness rather than colicky episodes with lethargy |
| Henoch-Schonlein purpura | Purpuric rash, arthritis; can also cause intussusception |
| Volvulus and other obstruction | Bilious vomiting with no mass or target sign; see intestinal obstruction |
What are the one-line facts to revise for exams?
- Definition: proximal segment (intussusceptum) enters distal segment (intussuscipiens); commonest type ileocolic.
- Age: usual 6 to 18 months, peak 4 to 9 months; boys more than girls, about 3:1.
- About 90% idiopathic (hypertrophied Peyer patches); about 10% have a lead point; lead points rise with age.
- Lead points: Meckel diverticulum, polyp, duplication cyst, appendix stump, lymphoma, HSP haematoma.
- Red currant jelly stool is late and uncommon; the triad (pain, mass, blood) is seen in about one-third.
- Ultrasound is test of choice: target (transverse) and pseudokidney (longitudinal) signs.
- Contrast enema signs: meniscus and coiled spring.
- Treatment: air or saline enema (success over 80%); surgery for peritonitis, perforation, shock or failure.
- RotaShield was withdrawn after an intussusception signal; current vaccines show at most a very low risk.