Intussusception is one of those “classic pediatrics” GI emergencies that shows up everywhere on Step 1: a baby with intermittent screaming, knees-to-chest, and a diaper full of blood and mucus. The trick is not just recognizing the buzzwords—but understanding why each symptom happens, what imaging you order, and when you go straight to the OR.
What is Intussusception?
Intussusception = telescoping of a segment of bowel into an adjacent distal segment (usually ileum into cecum).
- The proximal segment that invaginates is the intussusceptum
- The receiving distal segment is the intussuscipiens
Why it matters: telescoping drags mesentery with it → venous congestion → edema → bowel wall ischemia. If untreated: necrosis, perforation, peritonitis, shock.
Pathophysiology (Step 1 Mechanism You Should Be Able to Explain)
The sequence
- Lead point or hyperactive peristalsis pulls bowel inward
- Mesenteric vessels get compressed
- Venous outflow obstruction (happens first) → bowel wall edema
- Progression to arterial compromise → ischemia
- Mucosal sloughing → bleeding into lumen → “currant jelly” stool
- Potential perforation → pneumoperitoneum + sepsis
Why the pain is intermittent (high-yield)
- The bowel telescopes in bouts as peristalsis comes in waves → colicky, episodic pain with symptom-free intervals early on.
Epidemiology & Who Gets It
Typical Step vignette patient
- Age: 6 months to 3 years (peak around 6–18 months)
- Sex: more common in males
Common triggers/associations (HY)
- Often idiopathic in kids, but classically follows viral illness → lymphoid hyperplasia (Peyer patches) acting as a lead point
- In older children/adults, think a pathologic lead point (tumor, polyp, etc.)
High-Yield Etiologies & Lead Points
Children
- Idiopathic (most common)
- Post-viral lymphoid hyperplasia (Peyer patch enlargement)
“Don’t miss” lead points (esp. older kids)
- Meckel diverticulum
- Henoch–Schönlein purpura (IgA vasculitis) (bowel wall hematoma can serve as lead point)
- Polyps (e.g., Peutz–Jeghers—more Step 2 style)
- Lymphoma (esp. ileocecal region)
Adults (Step contrast point)
- Usually due to a lead point, often neoplasm (benign or malignant). Adult intussusception ≠ “air enema and discharge.”
Clinical Presentation (Recognize the Pattern)
Classic triad (but not always all present)
- Intermittent, colicky abdominal pain
- Vomiting (may become bilious if obstruction progresses)
- “Currant jelly” stool = blood + mucus from ischemic mucosa
Other high-yield findings
- Sausage-shaped abdominal mass (often RUQ)
- Lethargy can be prominent in infants (can look “out of proportion”)
- Signs of obstruction and dehydration as it worsens
Why “currant jelly” happens
Ischemia → mucosal sloughing/bleeding + mucous secretion → blood + mucus.
Diagnosis (What You Order and What You See)
First-line imaging in a stable child
Ultrasound is typically the diagnostic test of choice in pediatrics.
- Target sign / donut sign on transverse view
- Can also show pseudokidney sign on longitudinal view
Contrast/Air enema: diagnostic and therapeutic
- Air enema (or contrast enema) can confirm and reduce the intussusception
- Imaging classically shows:
- Coiled spring sign (contrast trapped between mucosal folds)
When to think “skip enema—go to surgery”
If any of the following are present:
- Peritonitis (rebound, guarding)
- Perforation
- Hemodynamic instability/sepsis
- Concern for a pathologic lead point (esp. older child/adult) depending on scenario
Treatment (Step 1 Algorithm)
Stable, no peritoneal signs
Pneumatic (air) enema reduction (often under fluoroscopy/US guidance)
- Therapeutic success is high
- Observe for recurrence (can recur, especially within 24–48 hours)
Unstable or complications (or failed enema)
Surgery
- Manual reduction and/or resection if necrotic bowel
- Surgery is also more likely if lead point suspected
Antibiotics?
- Not always required for uncomplicated cases, but given if perforation, peritonitis, or surgical management is needed.
Complications You Should Know
- Bowel ischemia and necrosis
- Perforation → peritonitis
- Sepsis/shock
- Recurrence after reduction
Differential Diagnosis (Quick Step Sorting)
| Condition | Key Clues | How It Differs |
|---|---|---|
| Malrotation with volvulus | Sudden bilious vomiting in neonate, rapid deterioration | Surgical emergency; “corkscrew”/abnormal SMA-SMV relationship |
| Meckel diverticulum | Painless lower GI bleeding in toddler | No colicky pain pattern unless it becomes a lead point |
| Hirschsprung disease | Delayed meconium, chronic constipation, abdominal distension | Not episodic colicky pain + currant jelly |
| Appendicitis | Periumbilical → RLQ pain, fever, anorexia | Older kids/teens, not classic currant jelly stool |
| Necrotizing enterocolitis | Premature infant, pneumatosis intestinalis | Different age + systemic illness pattern |
High-Yield Associations & Classic Vignette Triggers
Viral illness → Peyer patch hyperplasia
- Often described as “recent URI” or “recent gastroenteritis”
Age matters
- Infant/toddler: idiopathic/post-viral common
- Older child/adult: suspect lead point (Meckel, lymphoma, tumor)
Stool description
- “Currant jelly” is late-ish (ischemia) and not required to diagnose early.
Physical exam pearl
- Sausage-shaped mass + episodic crying with leg flexion is extremely testable.
First Aid Cross-References (Where This Lives in FA)
In First Aid (GI—intestinal obstruction/acute abdomen), intussusception is typically presented with:
- Telescoping bowel obstruction
- Currant jelly stools
- Sausage-shaped mass
- Air/contrast enema diagnostic + therapeutic
- Often linked to viral infection → Peyer patch hyperplasia
Use it as a “pattern recognition” anchor: episodic pain + currant jelly + target sign.
Rapid Review (What to Memorize)
10-second diagnosis
- 6–18 month old with intermittent colicky abdominal pain, vomiting, ± currant jelly stool, ± sausage-shaped mass → intussusception
Best initial test
- Ultrasound → target sign
Best initial treatment (stable)
- Air enema reduction
Red flags → surgery
- Peritonitis, perforation, unstable vitals, failed enema, or strong suspicion of a lead point
USMLE-Style Mini Check
Vignette: 9-month-old with episodic screaming, draws knees to chest, then calms down. Vomiting. One stool with blood and mucus.
Most likely diagnosis: Intussusception
Most likely imaging finding: Ultrasound “target sign”
Best next step (stable, no peritoneal signs): Air enema reduction