Target sign on ultrasound: bowel inside bowel · tap to expand
Pseudokidney sign (lengthwise view) · tap to expand
How bowel telescopes into bowel · tap to expand
🦵
Intussusception
Bowel telescopes into bowel and strangles its own blood supply. The colicky infant, the currant jelly stool, the target sign, and the enema that both finds it and fixes it.
A 9-month-old boy is brought in after several hours of sudden episodes where he screams and pulls his knees to his chest, each spell lasting a few minutes before he goes quiet and limp. One diaper held dark red, jelly-like stool. He is alert now, his belly is soft, and you feel a sausage-shaped fullness in the right upper abdomen. He has no fever and has never been on any medication.
What is your top suspicion?
Acute viral gastroenteritis
Intussusception
Hypertrophic pyloric stenosis
Midgut volvulus
Pathophysiology
Bowel Inside Bowel
One segment of intestine slides into the segment in front of it, like a collapsing telescope or a sock turned partway inside out as you peel it off your foot.
The two pieces
The inner tube that slides in is the intussusceptumThe bowel segment that telescopes inward, dragging its mesentery with it.. The outer sleeve that swallows it is the intussuscipiensThe receiving segment that the inner bowel slides into.. The common version is ileocolic: the last part of the small bowel (ileum) telescopes through the ileocecal valve into the colon.
Step 1: A lead point gets grabbed. Something that bulges into the lumen gets caught by the normal forward squeeze of the gut (peristalsis) and dragged downstream, pulling the bowel in behind it. In most babies there is no tumor, just swollen lymph tissue (Peyer patches) after a viral illness acting as the lead point.
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Step 2: The mesentery gets dragged in. The fan of tissue carrying the blood vessels (the mesentery) is pulled into the telescope and pinched between the layers.
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Step 3: Veins choke first. The pinched mesentery squeezes the low-pressure veins before the arteries, so blood backs up and the bowel wall swells with fluid (edema).
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Step 4: Swelling tightens the trap. The edema clamps the arteries too, and now the trapped bowel is starved of oxygen (ischemia).
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Step 5: Currant jelly stool. The starved lining sloughs off and bleeds, mixing with mucus into the classic currant jelly stool. This is a late sign: by the time you see it, the bowel is already in trouble.
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Step 6: Necrosis and perforation. Left alone, the dead segment perforates, spilling stool into the belly (peritonitis), then shock, then death.
★Most common cause of bowel obstruction in children 6 months to 3 years, with the peak right around 9 months. Most common location is ileocolic.
The punch: a telescoped segment strangles its own blood supply from the inside out. Currant jelly stool means you are already late. Move.
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Lead Points
What Started the Telescope
Tap each card. Front = the suspect. Back = how it leads the bowel in and the board clue that fingers it.
🦠
Lymphoid Hyperplasia
The default in babies
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Idiopathic (most infants)
Swollen Peyer patches after a viral illness act as the lead point.
The usual story in a well baby under 2 with no other findings.
Adenovirus and rotavirus are the classic preceding bugs.
This is why most cases need no tumor to explain them.
🔎
Meckel Diverticulum
Most common pathologic lead point
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Meckel diverticulum
Most common pathologic lead point overall in children.
Classic clue elsewhere: painless rectal bleeding from ectopic gastric mucosa.
Rule of 2s: 2% of people, 2 feet from the ileocecal valve, 2 years.
Found on a Meckel (technetium pertechnetate) scan.
🩸
HSP (IgA Vasculitis)
Purpura plus belly pain
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Henoch-Schonlein purpura
Vasculitis bleeds into the bowel wall: that intramural hematoma is the lead point.
Leads an ileoileal (small bowel into small bowel) intussusception.
Clue tetrad: palpable purpura on buttocks and legs, arthritis, abdominal pain, hematuria.
Often not reducible by enema; may need surgery.
⚠
Intestinal Lymphoma
The older kid red flag
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Burkitt / intestinal lymphoma
The lead point to fear in an older child (older than about 6).
Clues: recurrence, weight loss, night sweats, a firm fixed mass.
A tumor that peristalsis keeps grabbing.
Needs surgical resection and staging, not just an enema.
💉
Rotavirus Vaccine
Small, real, early
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Rotavirus vaccine link
The original rhesus-based vaccine (RotaShield) was withdrawn in 1999 for excess intussusception.
Current oral vaccines carry a small attributable risk, a few cases per 100,000.
Risk is greatest in the first week after the first dose.
Benefit in preventing severe rotavirus diarrhea still outweighs the small risk.
💡Hunt hard for a pathologic lead point when the patient is under 3 months, older than 2 to 3 years, or has recurrent intussusception. The classic idiopathic kind is a one-time event in a well infant.
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Presentation and Diagnosis
Read the Infant, Then the Ultrasound
The classic triad is famous but incomplete: the full set shows up in fewer than one in four children. Know the disguises.
The classic triad
Intermittent colicky pain. The infant draws the legs to the chest and cries inconsolably for a few minutes, then goes calm or limp between spells (every 15 to 20 minutes).
Currant jelly stool. Blood mixed with sloughed mucosa and mucus. A late finding that means ischemia is already underway.
Sausage-shaped mass. Classically in the right upper quadrant, with an empty feel in the right lower quadrant (the Dance sign).
Vomiting starts nonbilious and turns bilious (green) as the obstruction tightens.
🧠
The lethargy trap
Intussusception has a neurologic disguise. Some infants present mainly with episodic profound lethargy or altered consciousness, looking postictal or septic, with little overt belly complaint. The waxing and waning limpness mirrors the on-and-off colic. Anchoring only on a sepsis or meningitis workup is exactly how this gets missed. The lethargic infant with no clear source: feel the belly and image it.
Diagnosis
Ultrasound is first-line. It shows the target / donut / bull's-eye sign (concentric rings of bowel within bowel) on the transverse view and a pseudokidney sign lengthwise. No radiation, high sensitivity and specificity.
Abdominal X-ray can show a paucity of gas on the right or signs of obstruction, but its key job is to look for free air (perforation) before you ever attempt an enema.
The enema itself (air or contrast) is both the confirmatory test and the treatment, covered next.
★Concentric rings of bowel inside bowel on ultrasound plus episodic colic in a toddler equals intussusception. Target sign on US is the money image.
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Management
The Enema That Finds It and Fixes It
Most ileocolic cases never see a scalpel. Build the sequence, then decide who actually needs the OR.
Build the reduction sequence
Tap the three steps in the right order, one slot at a time. Get it wrong and you reset.
STEP 1empty
STEP 2empty
STEP 3empty
The air enema
The air (pneumatic) enema is the first-line treatment for ileocolic intussusception and is both diagnostic and therapeutic. The controlled pressure pushes the telescoped segment back out, like blowing into a glove finger that got pushed inward to pop it back. It reduces roughly 80 to 95% of ileocolic cases. A water-soluble contrast enema is the alternative.
Clinical Reasoning
Enema or OR?
Confirmed ileocolic intussusception. Pick the path.
Air (pneumatic) enema. It is the test and the treatment in one. The pressure reduces the telescope and you avoid an operation entirely.
Straight to the OR. Peritonitis, perforation, or shock makes the enema contraindicated: pushing pressure across a hole sprays contamination everywhere. Operate to reduce or resect.
🛡Indications for surgery instead of enema: peritonitis, perforation (free air), hemodynamic instability or shock, or a failed enema reduction. A pathologic lead point often needs surgery too.
🔄Recurrence is about 10% after enema reduction. Recurrence raises suspicion of a pathologic lead point, so go hunting.
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Board Walkthrough
Prove It
Seven original clinical vignettes, five dealt per round, answer choices shuffled, never repeating within a round. Tap a wrong answer first to see why it almost works, then read the glowing clues.
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Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated July 1, 2026 at 10:03 PM ET
Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.
