A target on transverse and a pseudokidney on longitudinal — then decide whether it is ileocolic (needs reduction) or transient small bowel (does not).
Orient first
- Intussusception is bowel telescoped into bowel, dragging its mesentery in with it. The mesentery inside the target is why the layers look concentric and why the blood supply is threatened.
- The distinction that changes management is ILEOCOLIC versus SMALL-BOWEL–SMALL-BOWEL. Ileocolic needs reduction; a short transient small-bowel intussusception usually resolves on its own.
- Size and location separate them: ileocolic is larger (typically over 25 mm outer diameter) and lies along the colon, classically in the right upper quadrant. Transient small bowel is smaller, shorter, and central.
Acquire the study
- High-frequency linear probe on an infant; curvilinear for a bigger child or a distended abdomen.
- Scan the whole colon systematically: start in the right iliac fossa, follow the ascending colon up, across the transverse, and down the descending — the intussusception sits somewhere along that path, most often subhepatic.
- Graded compression as for the appendix. A crying, guarding child defeats the study — settle them, feed if appropriate.
- Colour Doppler at low-flow settings to assess perfusion of the intussusceptum.
The manoeuvre
- On TRANSVERSE, look for the target / doughnut sign: concentric alternating hypo- and hyperechoic rings.
- On LONGITUDINAL, the same thing appears as the pseudokidney sign.
- Measure the outer diameter and the LENGTH of the segment — both separate ileocolic from transient.
- Assess flow within the intussusceptum with Doppler; absent flow suggests ischaemia and argues against attempted reduction.
- Look for TRAPPED FLUID between the layers — a predictor of failed reduction.
- Hunt for a LEAD POINT (Meckel diverticulum, duplication cyst, polyp, lymphoma, Henoch–Schönlein purpura), particularly outside the typical age range.
- Look for free fluid, and for pneumoperitoneum, which contraindicates reduction.
What confirms it
- A target lesion over about 25 mm outer diameter along the course of the colon is an ileocolic intussusception.
- A small central target under about 15 mm with a short segment and normal flow is usually transient small-bowel and needs observation rather than reduction.
What licenses you to exclude it
- A complete, careful survey of the whole colonic course with no target excludes ileocolic intussusception at the time of scanning.
- ⚠️ Intussusception can be INTERMITTENT. If symptoms are classic and the scan is negative, say that a negative study does not exclude an intermittent intussusception and that re-scanning during pain is appropriate.
The classic misread
- Stopping at the right iliac fossa — the commonest position is subhepatic.
- Reporting a transient small-bowel intussusception as if it needed an air enema.
- Missing perforation before reduction is attempted.
- Not looking for a lead point in a child outside the usual 3-month-to-3-year window.