Define Intussusception. Describe its causes and clinical features.

The Concept

Intussusception is the telescoping (invagination) of one segment of bowel into the lumen of the immediately distal segment, dragging its mesentery with it. This causes obstruction and, because the mesentery is compressed, progressive venous congestion → ischaemia → and eventually infarction of the intussuscepted bowel if not relieved. The commonest type is ileocolic.

Causes — Child VS Adult

The cause differs strikingly with age. In infants (the typical patient, 3 months–2 years) it is usually idiopathic, thought to follow lymphoid hyperplasia of the Peyer's patches after a viral illness, which acts as the lead point. In adults, by contrast, there is almost always a pathological lead point — a polyp, tumour or Meckel's diverticulum — so adult intussusception warrants a search for underlying disease.

Clinical Features

The classic infant presentation is episodes of severe colicky pain during which the child draws up the legs and screams, with pallor, alternating with calm intervals. There is vomiting, the passage of 'redcurrant jelly' stool (blood mixed with mucus — a late sign of ischaemia), and a palpable sausage-shaped mass, classically in the right upper quadrant.

Diagnosis & Management

Ultrasound is the investigation of choice, showing the characteristic 'target' or 'doughnut' sign in cross-section. In a stable child without peritonitis, treatment is non-operative reduction by an air (or contrast) enema, which is both diagnostic and therapeutic. Surgery is required if enema reduction fails, if there is peritonitis or perforation, or if a lead point is present (as in adults).

WHY Early Reduction Matters

Prompt treatment matters because a delayed intussusception progresses from simple obstruction to ischaemia and infarction of the trapped bowel, at which point enema reduction becomes unsafe and resection is needed. The passage of 'redcurrant jelly' stool is a warning that ischaemia has begun. This is why a stable child is investigated and reduced urgently, and why peritonitis contraindicates enema reduction.

The Bottom Line

Intussusception is telescoping bowel — idiopathic in infants, lead-point-driven in adults — recognised by colicky pain, redcurrant-jelly stool and a target sign on ultrasound, and reduced by air enema unless a lead point or peritonitis demands surgery.

A Note on Adult Intussusception

Adult intussusception differs fundamentally from the infantile form: because a pathological lead point (usually a tumour or polyp) is almost always present, enema reduction is inappropriate and surgical resection is the rule, both to relieve the obstruction and to remove and examine the causative lesion. Any adult with intussusception is therefore investigated for an underlying neoplasm.

Sausage-shaped mass with red-currant jelly stool in an infant.

• Intussusception = telescoping of bowel into the distal segment (usually ileocolic) → obstruction + ischaemia.
• Infants: idiopathic (lymphoid hyperplasia after viral illness); adults: pathological lead point (polyp, tumour, Meckel's).
• Colicky pain (child draws up legs), vomiting, 'redcurrant jelly' stool, sausage-shaped mass.
• Ultrasound shows 'target'/'doughnut' sign.
• Treat by air/contrast enema reduction (stable child); surgery if it fails, peritonitis/perforation, or a lead point.