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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Invagination of proximal bowel into distal bowel — ileocaecal junction in >90% of cases
- Peak age 3 months to 2 years (peak 5–10 months). Male:female 2:1
- Classic triad: intermittent colicky abdominal pain (episodic, drawing up legs), vomiting, redcurrant jelly stools (blood and mucus — LATE sign)
- Palpable sausage-shaped mass in RUQ. Absence of normal bowel in RIF (Dance sign)
- Diagnosis: abdominal USS showing target/doughnut sign
- Treatment: non-operative air or contrast enema reduction (75–80% success). Surgery if reduction fails, perforation, or peritonitis
Overview
Intussusception occurs when one segment of bowel invaginates into the adjacent distal segment, most commonly at the ileocaecal junction. This causes venous obstruction, oedema, and if untreated, arterial ischaemia, necrosis, and perforation. Most cases in children are idiopathic, thought to be triggered by lymphoid hyperplasia (Peyer patches) following viral infection (adenovirus, rotavirus). In children over 2 years, a pathological lead point should be considered (Meckel diverticulum, polyp, lymphoma, Henoch-Schonlein purpura).
Epidemiology
Intussusception is the most common cause of bowel obstruction in infants aged 3 months to 2 years. Incidence is approximately 1–4 per 1,000 live births. Peak age is 5–10 months. Male:female ratio 2:1. There was a historical association with the old rotavirus vaccine (RotaShield, withdrawn) but the current rotavirus vaccines have a very small excess risk.
Clinical Features
Symptoms
Intermittent colicky abdominal pain — episodes every 10–20 min, child draws legs up, screams, then appears well between episodes
Vomiting — initially non-bilious, becomes bilious as obstruction progresses
Passage of redcurrant jelly stool (blood and mucus) — a LATE sign indicating mucosal ischaemia
Lethargy or pallor between episodes — can be the main presenting feature
Refusal to eat
Signs
Palpable sausage-shaped mass in RUQ or epigastrium
Emptiness in RIF — Dance sign (caecum drawn up by intussusception)
Abdominal distension (if obstruction has progressed)
Blood and mucus on PR examination
Signs of shock: tachycardia, pallor, poor CRT (late — suggests bowel ischaemia or perforation)
Investigations
First-line
Abdominal ultrasoundInvestigation of choice — target sign (doughnut sign) on transverse view, pseudokidney sign on longitudinal view. Sensitivity >95%
Second-line
Abdominal X-rayMay show: soft tissue mass in RUQ, absence of caecal gas, signs of small bowel obstruction (dilated loops, air-fluid levels). Can be normal early
BloodsFBC, U&Es, group and save — pre-operative if surgery anticipated. Cross-match if shocked
Specialist
Air or contrast enema (therapeutic)Both diagnostic and therapeutic — see below
Management
BAPS and paediatric surgical guidelines1
Resuscitation
- IV access, fluid resuscitation if dehydrated or shocked
- NG tube if vomiting or abdominal distension
- Analgesia for pain
- NBM — anticipate procedure or surgery
2
Non-operative reduction
- Air enema (pneumatic reduction) is first-line — success rate 75–80%
- Performed under fluoroscopic guidance by a radiologist with surgical standby
- Contraindications: peritonitis, perforation, profound shock, or failed previous attempt
- Monitor for 24 h after successful reduction — recurrence in ~10% (usually within 48 h)
3
Surgical management
- Indicated if: non-operative reduction fails, peritonitis, perforation, or prolonged symptoms (>48 h)
- Manual reduction at laparotomy — gently squeeze the intussusceptum out (do not pull)
- Bowel resection if gangrenous or necrotic bowel, or pathological lead point found
- In children >2 years: look for pathological lead point (Meckel, polyp, lymphoma)
Complications
- Bowel ischaemia and necrosis: If untreated — leads to perforation and peritonitis
- Recurrence: ~10% after non-operative reduction, ~2–5% after surgery
- Perforation: Risk during enema reduction (~1%) — requires immediate surgery
- Short bowel syndrome: If extensive resection needed (rare)
UKMLA Exam Tips
- 1Classic triad: colicky pain (drawing up legs) + vomiting + redcurrant jelly stool — but the full triad is present in only ~30%
- 2Redcurrant jelly stool is a LATE sign — do not wait for it to diagnose
- 3Sausage-shaped mass in RUQ + Dance sign (empty RIF) on examination
- 4USS showing target/doughnut sign is the diagnostic test of choice
- 5Air enema is both diagnostic and therapeutic — 75–80% success rate
- 6In children >2 years: think pathological lead point (Meckel diverticulum, polyp, lymphoma, HSP)
- 7Can present as lethargy/pallor between episodes with NO abdominal pain — classic atypical presentation
practicetest your knowledge on intussusceptionApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — paediatrics and beyond.
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