• Intussusception is the invagination (or telescoping) of one part of bowel into another.
  • Most typically it involves the ileum into the caecum however can occur anywhere in the bowel.
  • The risk is ischemia of the ‘trapped’ bowel leading to necrosis and sepsis.
  • It may occur at any age but commonly occurs in the 2 month to 2 year age group with a peak incidence at 5 to 9 months.
  • Most common cause of bowel obstruction in children < 3yr old. M > F
  • Fatal if untreated.
intussusception schematic
Schematic of intussusception anatomy. The proximal bowel (intussuseptum) telescopes into the distal bowel (intussuscipiens).
Ultrasound appearances:
  • ‘Pseudo kidney’
  • Target sign

The ileum has invaginated into the cecum.

The cecum is called the intussuscipiens.

The ileum is called the intussusceptum.

Intussusception ‘pseudo kidney’ sign.

The ileum is the intussuseptum and has telescoped into the caecum (intussusipiens).

Axial CT scan showing the intussusception in the RIF.

Coronal CT scan showing the intussusception in the RIF.

Clinical flowchart for intussusception.

REF: The Royal Children’s Hospital,
Melbourne Australia.

Patho-physiology of Intussusception


  • Idiopathic/Unknown aetiology.
  • In a small percentage, there may be a ‘lead point’. This is an anatomical or pathological structure contributing the the intussuseption. EG tumour, meckles diverticulum or haematoma. Non surgical resolution is less successful when a lead point is present.
  • Some researchers are suggesting a post viral association. Particularly related to proliferation/reactive Peyer’s patches (learn more) acting as a lead point.
  • Also has been linked to an older type of Rota virus vaccination (REF : NEJM).


  • Acute onset of severe pain (spasmodic, but increasing in frequency)
  • May be a palbable mass.
  • Mixture of blood and mucous causes ‘current jelly’ stools. Occurs as the condition advances. Does not have to be present.
  • Most common cause of bowel obstruction in children < 3yr old. M > F
Intussusception diagram
Intussusception diagram. REF Olek Remesz wiki-pl Orem, commons Orem, CC BY-SA 3.0, via Wikimedia Commons

Mesenteric lymph nodes adjacent to the distal ileum.

Scanning Protocol

Preparation & Equipment

  • No preparation is needed.
  • Supine.
  • Begin with a curvilinear probe to obtain an overview of the abdomen for masses and free fluid.
  • A linear probe (largest foot print available). Ideally 8-12MHz.
  • A curvi-linear probe for larger/deeper structures depending on the age and habitus of the paediatric patient.
  • Warm gel and warm envirnonment.

Scan technique

  • Be as gently as possible.
  • Begin with a curvilinear probe to obtain an overview of the abdomen for masses and free fluid.
  • If there is a palpable mass or painful focus, scan directly on that area.
  • If not, scan medially in the RIF.
  • Begin at the level  to ASIS in a transverse plane.
  • Slide superiorly looking for the caecum.
  • Sweep superiorly and inferiorly in a progressive manner towards umbilicus.
  • If no pathology/cause for symptoms is identified, assess all the viscera (liver, kidneys, adrenals etc).
  • Also check the orientation of superior mesenteric artery to be left of the superior mesenteric vein. Image in a transverse plane. If reversed, suspect volvulus. and look for “bowel whirlpool”.
  • If intussuseption or other bowel pathology identified, ensure vascularity is present in the bowel wall using colour doppler.

Differential diagnoses

There are many causes of abdominal pain in an infant. These include:

  • Appendicitis
  • Colic
  • Constipation
  • Mass
  • Infection

Basic Hardcopy Imaging

An intusseption series is an urgent, targetted scan  & is actually an examination for the cause for abdominal pain. It should include images of the relevant anatomy investigated:

  • SMA, SMV orientation
  • Colour doppler of bowel wall.
  • Any pathology identified
  • Any free fluid identified.

Document any pathology found in 2 planes, including measurements and any vascularity.