Intussusception

Definition/diagnostic criteria
Intussusception is the telescoping of one segment of the intestine into an adjacent segment, most commonly the ileum into the colon. This leads to obstruction, ischaemia, and potentially bowel necrosis if untreated. It is the most frequent cause of intestinal obstruction in children aged 6 months to 3 years but can occur in older children and adults, where an underlying pathology (e.g., polyp, tumour) is more common.

Epidemiology
Intussusception predominantly affects infants and young children, particularly between 6 and 18 months. It is rare in neonates and uncommon in children over 3 years. The annual incidence in the UK is approximately 1-4 per 1,000 live births. The condition is slightly more common in males than females, with a male-to-female ratio of about 3:2. The exact cause of intussusception is often idiopathic in young children, but viral infections (e.g., adenovirus) and recent rotavirus vaccinations (mainly the older versions, pre-2006) have been implicated in some cases.

Diagnosis

Clinical features
The classic triad of symptoms in intussusception includes intermittent abdominal pain, vomiting, and “red currant jelly” stools, although this triad is only seen in about 15% of cases. The pain is often colicky, with periods of crying and irritability followed by lethargy. Vomiting is typically non-bilious early on, becoming bilious if the obstruction progresses. Abdominal distension and palpable mass, often described as a “sausage-shaped” lump, may be felt in the right upper quadrant or mid-abdomen. Lethargy or altered mental status can occur due to shock or dehydration, especially in severe or prolonged cases.

Investigations
Ultrasound is the imaging modality of choice, showing the characteristic “target” or “doughnut” sign in cross-section and the “pseudo-kidney” sign on longitudinal views, which confirm the diagnosis. Sensitivity and specificity of ultrasound for intussusception approach 98-100%. Plain abdominal X-rays may show signs of bowel obstruction, such as air-fluid levels or distended bowel loops, but they are not diagnostic. If there is concern for bowel perforation or ischaemia, an abdominal X-ray can be useful to rule out free air under the diaphragm.

In children presenting atypically or in adults, CT or MRI may be required to assess for underlying pathology such as tumours or polyps causing the intussusception. Blood tests may show dehydration or electrolyte imbalances, and a raised white cell count may indicate infection or necrosis.

Treatment

Non-surgical management
Most children with intussusception can be treated non-surgically with air or contrast enema reduction. Air enema reduction is the preferred method in the UK, achieving success in 75-95% of cases. This procedure is both diagnostic and therapeutic, as the pressure of the enema helps reduce the intussusception by pushing the telescoped bowel back into its normal position.

Surgical management
Surgery is indicated if enema reduction fails, if there is evidence of bowel perforation, or if the child presents late with signs of peritonitis or sepsis. Surgical reduction involves manual reduction of the intussusception or resection of necrotic bowel segments in severe cases. Recurrence after successful non-surgical reduction occurs in approximately 10% of cases, often within 48 hours, and repeat enema reduction can be attempted in non-complicated cases.

Prognosis
If diagnosed and treated promptly, the prognosis for intussusception in children is excellent, with over 90% achieving full recovery. Delayed diagnosis can lead to bowel necrosis, perforation, sepsis, and death. Long-term complications are rare, though recurrent intussusception can occur in about 5-10% of cases. In adults, intussusception is often secondary to an underlying pathology, and the prognosis depends on the cause, such as malignancy.