What is intussusception?

What is Intussusception

Intussusception is the telescoping of one segment of the gastrointestinal tract (the intussusceptum) into an immediately adjacent distal segment (the intussuscipiens), creating a bowel-within-bowel configuration that can lead to venous congestion, edema, vascular compromise, and potentially bowel necrosis if not promptly treated. 1, 2

Anatomic Definition and Mechanism

• The proximal bowel segment invaginates into the lumen of the distal bowel, carrying the mesentery forward and trapping it between the overlapping layers 3
• This trapped mesentery undergoes twisting or severe constriction of its vessels, which may result in vascular compromise with subsequent edematous thickening of the involved bowel 3
• If timely intervention is not undertaken, ischemic necrosis develops from the compromised blood supply 3, 4

Epidemiology and Age-Related Differences

Pediatric Population

• Intussusception is one of the most common causes of intestinal obstruction in children between 3 months and 6 years of age 1
• In young infants, it is unusual in the first 3 months of life 5
• Pediatric cases are typically idiopathic (no identifiable lead point) 5

Adult Population

• Intussusception accounts for only about 1% of intestinal obstruction cases in adults 1
• The incidence is approximately 2 per 1,000 cases per year worldwide 4
• Unlike children, 86-93% of adult cases have an identifiable underlying pathologic lesion serving as a "lead point" 6, 7
• Idiopathic causes occur in only 8-20% of adult patients 1, 8

Anatomic Location

• Small bowel intussusception is most common in adults 1, 8
• Large bowel involvement occurs less frequently and rarely involves only the colon 8
• Specific subtypes include ileoileal, ileocolic, and colo-colonic intussusception 1, 2

Underlying Pathology (Lead Points)

Benign Causes (Small Bowel)

• Hamartomas, lipomas, inflammatory polyps, adenomas, and leiomyomas are the most common benign causes 2
• Meckel's diverticulum, adhesions, and inflammatory bowel disease can also serve as lead points 7
• Ileal fibromas are uncommon but must be considered in the differential diagnosis 2

Malignant Causes

• In the large intestine, malignant tumors (usually adenocarcinomas) are more common than benign lesions 2
• Leiomyosarcoma is a rare mesenchymal malignant lesion that can cause small bowel intussusception 4
• Overall, benign or malignant tumors account for approximately 65% of adult intussusception cases 3

Special Circumstances

• Post-bariatric surgery patients can develop intussusception due to modified intestinal motility, staple lines, and anatomic peculiarities 6
• Post-colonoscopy intussusception can occur, though it is rare 1

Clinical Presentation

Pediatric Presentation

• Crampy, intermittent abdominal pain is characteristic 5
• Progression to bloody stools (classically described as "currant jelly" stools) 5
• Lethargy may develop as the condition progresses 5

Adult Presentation

• The clinical presentation is non-specific with variable manifestations, predominantly those of intestinal obstruction 2, 4
• Symptoms may have acute, intermittent, or chronic onset 2
• Abdominal pain with signs of bowel obstruction is the most common presenting symptom 4
• Nausea and vomiting frequently accompany the pain 4

Diagnostic Imaging

Pediatric Imaging

• Ultrasound is the preferred first-line imaging modality, offering approximately 80% sensitivity and near-100% specificity while avoiding ionizing radiation 9
• Plain abdominal radiographs should be obtained initially to assess for bowel gas patterns and obstruction 5

Adult Imaging

• Contrast-enhanced CT scan is the mandatory diagnostic modality for suspected adult intussusception 6, 7
• CT demonstrates the intussusception, identifies the lead point, and detects complications such as ischemia or perforation with approximately 80% sensitivity and approaching 100% specificity 6
• The pathognomonic imaging appearance is a bowel-within-bowel configuration with or without contained fat and mesenteric vessels, creating the classic "bulls-eye" or "target sign" with concentric rings 3, 4

CT Findings Suggesting Vascular Compromise

• Severe engorgement or twisting of mesenteric vessels 3
• Loss of the normal layered bowel wall pattern 3
• Accumulation of extraluminal fluid collection 3
• Evidence of bowel perforation 3