Pediatrics
Intussusception
~12 min read6 sections
Intussusception is the telescoping of a proximal segment of bowel (intussusceptum) into the lumen of an adjacent distal segment (intussuscipiens), creating a functional obstruction and compromising mesenteric blood supply. It is the most common cause of acute intestinal obstruction in children between 6 months and 3 years of age, with peak incidence at 12-18 months. The annual incidence is approximately 1-4 cases per 1,000 live births in developed countries, with a slight male predominance (1.5-2:1 ratio). While 90-95% of cases are idiopathic (primary intussusception), secondary intussusception occurs when anatomical abnormalities or pathological lead points predispose to invagination. Understanding intussusception is critical for board examinations because prompt diagnosis and early intervention can prevent morbidity and mortality, particularly given the efficacy of non-operative reduction techniques.
The development of intussusception involves mechanical invagination of bowel and secondary vascular compromise. The following mechanisms explain the clinical manifestations:
- Mechanical obstruction from bowel invagination: In primary intussusception, hypertrophied Peyer's patches (lymphoid tissue in the terminal ileum) or mesenteric lymph nodes, often secondary to viral prodromata (adenovirus, rotavirus), serve as lead points. The thickened tissue creates a focal area that acts as an intraluminal mass. Peristalsis then propels this segment distally, causing it to telescope into the adjacent bowel. This typically results in ileocolic intussusception (75-90% of cases), where the terminal ileum invaginates into the colon at the ileocecal valve. Less commonly, ileoileal (10-20%) or colocolic (<5%) intussusceptions occur. The invaginated segment obstructs the bowel lumen, preventing aboral passage of intestinal contents and causing abdominal pain with a cyclic pattern (typically every 15-30 minutes) corresponding to peristaltic waves attempting to overcome the obstruction.
- Mesenteric vascular compromise and ischemia: As the intussusceptum telescopes into the intussuscipiens, the mesentery of the invaginated segment becomes compressed and tented. Progressive venous congestion occurs before arterial compromise, leading to mucosal edema and bleeding. If reduction does not occur spontaneously or therapeutically, progressive arterial insufficiency develops, causing transmural ischemia, necrosis, and perforation. The mucosa is most vulnerable and typically shows bleeding and ulceration before full-thickness necrosis develops. This explains the "currant jelly" stool—a mixture of blood and mucus reflecting mucosal ischemia. The timing of vascular compromise is critical: reversible changes may persist for 24-48 hours, but irreversible transmural necrosis typically develops after 24-72 hours of complete ischemia, though this is highly variable.
- Inflammatory cascade and bacterial translocation: Mucosal injury from ischemia triggers local inflammation and increases intestinal permeability. Bacterial translocation across the compromised epithelium can occur, leading to bacteremia and potential sepsis if perforation develops. The presence of inflammatory mediators (cytokines, prostaglandins) amplifies the local tissue injury and may contribute to systemic symptoms including fever and lethargy that can be disproportionate to local findings.
- Fluid sequestration and electrolyte derangements: Bowel obstruction causes accumulation of fluid proximal to the obstruction due to continued secretion and impaired reabsorption. This third-spacing of fluid leads to hypovolemia, dehydration, and potential hypokalemia and hyponatremia, particularly if vomiting is prominent. The duration and completeness of obstruction determine the degree of fluid shifts and metabolic derangement.
- Primary (idiopathic) intussusception—viral prodrome and lymphoid hypertrophy (90-95% of cases): Accounts for the vast majority of cases in children aged 6 months to 3 years. Rotavirus, adenovirus, and other viral pathogens cause hypertrophy of Peyer's patches and mesenteric lymph nodes in the terminal ileum, which then serve as lead points for invagination. The seasonal variation in intussusception incidence (peak in spring/summer in some regions, correlating with rotavirus and adenovirus circulation) and the frequent history of antecedent viral illness support this mechanism. The introduction of rotavirus vaccines has modestly decreased intussusception incidence in some populations. Post-immunization intussusception has been rarely associated with rotavirus vaccines (particularly RotaShield, which was withdrawn), occurring at a rate of approximately 1 case per 10,000-100,000 vaccinated infants; current vaccines have much lower risk (estimated 1-2 cases per 100,000 vaccinated).
- Secondary intussusception with anatomical lead points (5-10% of cases): More common in children >3 years of age or those with known predisposing conditions. Meckel's diverticulum (present in ~2% of the population) is the most common pathological lead point in children >3 years; heterotopic gastric mucosa within the diverticulum may cause inflammation and hypertrophy, serving as a lead point. Other lead points include lymphoma (particularly in older children and adolescents), polyps, duplication cysts, CF-related meconium ileus equivalents, and inflammatory lesions. In adults, intussusception is almost always secondary to a lead point such as neoplasm, polyp, or stricture.
- Immunomodulation and lymphoid proliferation: Enhanced lymphoid response to antigen exposure or immunization may increase risk. Children with recent immunizations (live or inactivated) have a transiently increased risk of intussusception over the subsequent 1-2 weeks, though the absolute risk remains low.
- Age and anatomical factors: The tight anatomical fit of the ileocecal valve predisposes to ileocolic intussusception. The developmental involution of Peyer's patches after age 3 years explains the rarity of primary intussusception in older children and adults.
The clinical presentation varies based on the duration of intussusception, completeness of obstruction, and presence of vascular compromise:
- Severe intermittent (colicky) abdominal pain—hallmark symptom: The classic presentation is sudden onset of severe, crampy abdominal pain in a previously well child, typically described as occurring every 15-30 minutes (though can range from minutes to hours). Pain corresponds to peristaltic attempts to overcome the mechanical obstruction. Between episodes, the child may appear relatively comfortable or even playful (though lethargic), creating a characteristic pattern that should raise high suspicion for intussusception. The pain is often accompanied by the child pulling the knees to the chest and crying. With progression or complete obstruction, pain may become more constant. The sudden onset and severe nature, contrasting with the child's apparent wellness during pain-free intervals, are classic board features.
- Bilious vomiting and refusal to feed: Results from the mechanical obstruction leading to gastric distension and triggering the vomiting center. Initially vomiting may be non-bilious, but becomes bilious with progression as the obstruction is distal to the ampulla of Vater. Persistent vomiting contributes to dehydration and electrolyte abnormalities.
- "Currant jelly" or bloody stools—sign of advanced disease: Occurs in 40-75% of cases and represents mucosal bleeding from ischemia. The stool appearance (a mixture of blood, mucus, and stool) is pathognomonic when present and indicates vascular compromise and possible transmural involvement. However, absence of bloody stools does not exclude intussusception. Onset is often delayed relative to pain onset, typically occurring after 12-24 hours of intussusception. The presence of "currant jelly" stools warrants urgent evaluation and treatment.
- Palpable abdominal mass (sausage-shaped mass in the right upper quadrant or right flank): Detected on physical examination in approximately 50-70% of cases. The mass represents the intussusceptum and surrounding intussuscipiens. Best appreciated with the child relaxed (sometimes easier with sedation or analgesia). In ileocolic intussusception, the mass may be felt in the right upper quadrant, right flank, or along the ascending colon. In ileoileal intussusception, the mass may be more central or periumbilical. The classic teaching is that absence of a palpable mass does not exclude the diagnosis.
- Right lower quadrant tenderness and abdominal distension: Localized tenderness may be present over the site of intussusception. With progression and development of peritonitis from perforation, diffuse tenderness and guarding develop. Abdominal distension reflects bowel obstruction with gas accumulation proximal to the obstruction.
- Altered mental status and fever—concerning signs: Some children present with lethargy, irritability, or drowsiness disproportionate to apparent illness severity, raising concern for systemic toxicity from ischemia or early sepsis. Low-grade fever is common in primary intussusception (likely from mucosal inflammation), while higher fever (>39°C) should raise concern for perforation and peritonitis. Shock (hypotension, tachycardia, poor perfusion) indicates advanced disease with significant third-spacing or peritonitis.
- Clinical variants and atypical presentations: Intussusception can present with diarrhea (from mucosal inflammation and ischemia), mimicking gastroenteritis. Some children present with only abdominal pain without vomiting or bloody stools, leading to delayed diagnosis. In infants, the presentation may be subtle with only irritability and poor feeding. Recurrent intussusception (typically within 24-48 hours after successful reduction) occurs in 5-10% of cases after non-operative reduction and should be considered if symptoms recur after apparent successful treatment.
The diagnosis of intussusception is established through clinical suspicion combined with imaging confirmation:
- Clinical history and physical examination: The classic presentation of sudden-onset severe intermittent abdominal pain in a child aged 6 months to 3 years should immediately raise suspicion for intussusception. A history of viral prodrome or recent immunization increases pretest probability. Physical examination findings include a palpable sausage-shaped mass, visible peristaltic waves, right lower quadrant tenderness, and a "empty right lower quadrant" (Dance sign—a subtle finding indicating absence of normal colonic gas in the right lower quadrant due to displacement by the intussusceptum). The presence of these findings, particularly the combination of classic pain pattern and palpable mass, may warrant urgent imaging without delay.
- Abdominal radiography (plain films): Often the initial imaging modality, though sensitivity is low (approximately 40-60% for diagnosis). Findings include signs of bowel obstruction (dilated small bowel loops, multiple air-fluid levels on upright films) and absence of colonic gas distal to the obstruction. The "target sign" or "doughnut sign" may occasionally be visible on anteroposterior views, representing the intussusceptum in cross-section. However, plain films cannot definitively exclude intussusception, and normal or nonspecific films should not delay further imaging if clinical suspicion remains high.
- Ultrasound—imaging modality of choice for diagnosis: Ultrasound is highly sensitive (85-100%) and specific (95-99%) for intussusception and is the first-line imaging study in most pediatric centers, particularly for therapeutic intent. The "target sign" or "doughnut sign" on transverse images is characteristic and is created by the central echogenic core of the intussusceptum surrounded by hypoechoic edematous bowel wall and mesentery of the intussuscipiens. Longitudinal images show the "pseudokidney sign" as the intussusceptum appears as an elliptical hypoechoic mass. Measurement of the transverse diameter of the intussusception on the maximum cross-sectional image is important: diameters >26-28 mm may be associated with a lower success rate for non-operative reduction. Doppler ultrasound demonstrating loss of mesenteric blood flow in the intussusceptum suggests advanced ischemia and transmural necrosis, which is a contraindication to non-operative reduction. Ultrasound also identifies fluid-filled loops, free fluid (suggesting perforation), and rarely, a lead point (such as a Meckel's diverticulum or duplicate cyst).
- CT imaging: Less commonly used as primary imaging in typical pediatric intussusception but may be employed in cases with atypical presentations or suspected secondary intussusception. CT shows the intussusceptum as an enhancing mass with target-like appearance and may identify lead points such as lymphoma, polyps, or duplication cysts. CT is more sensitive for detecting perforation and peritonitis but involves radiation exposure and is generally reserved for cases with diagnostic uncertainty.
- Contrast enema (fluoroscopic or CT): Historically used for both diagnosis and therapeutic reduction, now largely replaced by ultrasound for diagnosis. However, contrast enema may be employed when ultrasound is inconclusive or unavailable. Under fluoroscopy, the characteristic "coiled spring" or "concertina" appearance represents the compressed intussusceptum within the proximal colon. A filling defect or abnormal termination of the barium column at the ileocecal valve suggests ileocolic intussusception. Contrast enema can simultaneously provide therapeutic reduction if performed under controlled conditions.
- Diagnostic criteria and scoring systems: There is no formal scoring system for intussusception diagnosis; diagnosis is primarily clinical and radiological. Diagnostic criteria include: (1) clinical suspicion based on age, pain pattern, and vomiting; (2) supportive ultrasound findings (target or pseudokidney signs); (3) evidence of bowel obstruction on imaging; and (4) exclusion of other diagnoses. The combination of classic clinical presentation plus characteristic ultrasound findings is sufficient for diagnosis and typically warrants immediate treatment.
- Differential diagnosis: Must consider other causes of acute abdominal pain and obstruction in young children, including acute gastroenteritis (though vomiting is less persistent and pain is less severe), appendicitis (pain typically periumbilical initially, then localizes to right lower quadrant; no intermittent pain pattern), mesenteric adenitis (less acute pain, no palpable mass), small bowel obstruction from adhesions (history of prior surgery), volvulus (more acute presentation with severe pain and shock), and malrotation. The classic presentation of intussusception with intermittent pain and palpable mass should readily distinguish it from these conditions.
Treatment of intussusception is divided into non-operative and operative approaches, with the choice guided by clinical stability, duration of symptoms, imaging findings, and signs of perforation or ischemia:
- Non-operative reduction via ultrasound-guided hydrostatic or pneumatic enema—first-line treatment: In carefully selected patients without clinical signs of perforation, peritonitis, or shock, non-operative reduction has a success rate of 80-90% and is preferred to avoid laparotomy. Hydrostatic (saline) or pneumatic (air or CO₂) reduction can be performed under real-time ultrasound guidance. The mechanism involves gentle, sustained pressure transmitted through the contrast medium or gas column to overcome the mechanical obstruction and gradually dislodge the intussusceptum from the intussuscipiens. Contraindications to non-operative reduction include: signs of perforation (free intraperitoneal air, focal peritonitis), clinical shock or severe sepsis, complete obstruction for >48-72 hours with evidence of necrosis on imaging (absent mesenteric blood flow, bowel wall thickening >5 mm), or imaging findings suggesting a pathological lead point. The child should be pre-treated with IV hydration to correct dehydration and electrolyte abnormalities, and broad-spectrum antibiotics should be administered given the risk of bacterial translocation. If reduction fails, the procedure is typically abandoned and surgical intervention is pursued.
- Surgical reduction (open or laparoscopic)—second-line therapy or definitive treatment for complicated cases: Indicated if non-operative reduction fails, is contraindicated, or if signs of perforation or peritonitis are present. Manual reduction is performed by gently applying sustained pressure to the intussuscipiens to dislodge the intussusceptum (analogous to pressure applied during enema reduction but performed under direct visualization). The surgeon carefully assesses bowel viability; if the involved segment appears necrotic (black or dark appearance, lack of pulsatile bleeding, failure to brighten with application of warm saline-soaked gauze), resection with primary anastomosis is performed. The extent of resection depends on the segment involved; ileocolic intussusception typically requires resection of the terminal ileum and proximal colon if necrotic. Laparoscopic reduction has increasingly become available and offers the advantages of minimally invasive surgery with shorter recovery time. Resection is necessary in approximately 10% of cases requiring surgery.
- Management of secondary intussusception and associated lead points: