Intussusception
Intussusception occurs when one segment of intestine telescopes into the segment immediately adjacent to it, in the same way a collapsible telescope folds into itself. The inner segment is carried forward by normal peristalsis, dragging its blood supply with it, which leads to swelling, obstruction, and—if the process continues—compromised blood flow to the trapped bowel. It is the most common cause of bowel obstruction in infants and toddlers, where it usually occurs without an identifiable structural cause and is typically treated non-surgically with an air or contrast enema. In adults it is uncommon and behaves quite differently: a discrete lesion such as a polyp or tumor is usually acting as the lead point, and surgery is generally required. Imaging is central to diagnosis, with ultrasound the test of choice in children and CT the primary test in adults.
What is it?
In intussusception, a segment of bowel—called the intussusceptum—slides into the lumen of the segment immediately downstream of it, called the intussuscipiens. Peristalsis, the normal forward-propelling contraction of the intestine, then continues to draw the inner segment further along, much as a sleeve pulls inside itself.
The critical detail is that the inner segment does not travel alone. It drags its mesentery—the fold of tissue carrying its blood vessels—in with it. That mesentery becomes compressed between the two layers of bowel. Venous drainage is obstructed first, causing the trapped segment to swell, which worsens the compression. Lymphatic drainage is impaired, mucus and fluid accumulate, and the mucosa becomes congested and begins to bleed, producing the blood-and-mucus stool classically described as currant-jelly. If the process continues, arterial supply is eventually compromised, and the trapped bowel can become ischemic, necrotic, and ultimately perforate. This progression is why intussusception is treated urgently rather than observed.
The most common location by far is at the ileocecal region, where the terminal ileum telescopes into the cecum and ascending colon—termed ileocolic intussusception. Other configurations include ileoileal, colocolic, and jejunojejunal, and these are relatively more common in adults and in small bowel intussusception associated with lead points.
Pediatric and adult intussusception are best understood as two related but distinct conditions.
In infants and young children, the great majority of cases are idiopathic, meaning no discrete anatomical lesion is found. The leading explanation involves hypertrophy of Peyer’s patches—collections of lymphoid tissue in the wall of the terminal ileum—following a viral infection. The enlarged lymphoid tissue creates a subtle bulge that peristalsis can catch and draw forward. This mechanism fits the observed clustering after respiratory and gastrointestinal viral illnesses, particularly adenovirus, and the peak incidence between roughly 5 and 10 months, when lymphoid tissue is prominent and viral exposures are frequent.
A structural lead point is identified in a minority of children, and this becomes more likely with increasing age, in recurrent cases, and outside the typical age window. Recognized lead points in children include a Meckel diverticulum, intestinal polyps, duplication cysts, lymphoma, and vascular lesions. Two systemic conditions warrant particular mention: Henoch-Schönlein purpura (IgA vasculitis), which can cause bowel wall hematoma acting as a lead point and often produces small bowel rather than ileocolic intussusception, and cystic fibrosis, where thick inspissated stool can serve the same role.
A note on rotavirus vaccination is worth including because it is a common parental concern. The first licensed rotavirus vaccine was withdrawn in 1999 after a clear association with intussusception. Current rotavirus vaccines have been studied extensively and carry a very small increased risk—on the order of a few additional cases per 100,000 vaccinated infants, concentrated in the week after the first dose. Major health authorities continue to recommend rotavirus vaccination because the benefit in preventing severe rotavirus gastroenteritis, hospitalization, and death substantially outweighs this small risk. Parents with questions should discuss them with their pediatrician.
In adults, the picture is different. A pathologic lead point is found in the large majority of cases, and identifying it is the point of the evaluation. In the small bowel, lead points include benign lesions such as lipomas, adenomas, hamartomatous polyps (including those of Peutz-Jeghers syndrome), inflammatory fibroid polyps, Meckel diverticulum, and adhesions, alongside malignant causes including metastatic disease—melanoma is a classic small bowel metastatic lead point—lymphoma, and small bowel adenocarcinoma. In the colon, malignancy accounts for a considerably higher proportion of lead points, with adenocarcinoma the most common. Postoperative intussusception can occur following bariatric or other bowel surgery, and celiac disease and other conditions altering bowel motility can produce transient small bowel intussusception.
That last point is important and increasingly relevant: short-segment, non-obstructing small bowel intussusception is now identified fairly often as an incidental finding on CT performed for other reasons. These transient intussusceptions typically involve a short segment, lack a lead point, cause no bowel dilation upstream, and resolve spontaneously without treatment. They generally do not require intervention, though they may prompt evaluation for underlying conditions such as celiac disease when the clinical picture fits.
Symptoms in infants and young children follow a pattern that is distinctive when present in full but frequently incomplete.
The classic triad is intermittent severe abdominal pain, a palpable sausage-shaped abdominal mass, and currant-jelly stool. All three are present together in only a minority of children, and waiting for the full triad delays diagnosis.
The pain is episodic and dramatic. Episodes typically last minutes, during which an infant may cry inconsolably and pull the knees to the chest, followed by intervals in which the child seems settled, quiet, or even asleep. This cyclical pattern with apparently normal intervals is characteristic and is often what prompts caregivers to seek care.
Vomiting is common and may progress from non-bilious to bilious as obstruction develops. Lethargy deserves particular emphasis: some infants present primarily with striking listlessness or altered responsiveness, sometimes mimicking a neurological or septic illness, and this presentation is a well-recognized cause of delayed diagnosis.
Currant-jelly stool—stool mixed with blood and mucus—is a relatively late finding reflecting mucosal ischemia. Its absence does not exclude intussusception, and treatment should not await it. Some infants have occult blood on rectal examination before visible bleeding appears.
In adults, presentation is often more indolent. Intermittent crampy abdominal pain recurring over weeks or months is typical, sometimes with nausea, vomiting, distension, weight loss, or rectal bleeding. Because symptoms wax and wane as the intussusception reduces and recurs, adults are frequently investigated for other causes before the diagnosis is made, and it is sometimes discovered incidentally on imaging performed for the underlying tumor.
Diagnosis is imaging-based.
Ultrasound is the test of choice in children, with high sensitivity and specificity in experienced hands and no radiation exposure. In cross-section, the concentric layers of bowel produce a target or doughnut sign; viewed longitudinally, the appearance is described as a pseudokidney. Ultrasound also assesses blood flow within the involved segment with Doppler, identifies trapped fluid and lead points, and can detect features predicting a lower chance of successful enema reduction.
CT of the abdomen and pelvis with intravenous contrast is the primary test in adults. It demonstrates the bowel-within-bowel configuration, shows mesenteric fat and vessels drawn into the intussusceptum, identifies upstream obstruction, and—most importantly in adults—looks for a lead point and evidence of malignancy elsewhere. CT also detects complications including ischemia and perforation.
Abdominal X-rays may show signs of obstruction, a soft tissue mass, or absence of gas in the right lower quadrant, but they are neither sensitive nor specific and a normal X-ray does not exclude the diagnosis.
Contrast or air enema occupies a unique dual role in children, serving simultaneously as a confirmatory test and the primary treatment.
Blood tests assess hydration status, electrolytes, and markers of infection or ischemia. They support management but do not make the diagnosis.
The differential diagnosis in children includes gastroenteritis, appendicitis, malrotation with midgut volvulus, incarcerated hernia, Meckel diverticulum bleeding, colic, and—because of the lethargy presentation—sepsis and central nervous system conditions. In adults it includes other causes of small bowel obstruction, tumors, inflammatory bowel disease, and mesenteric ischemia.
Important to Know
Intussusception is treated as an urgent condition, and the approach differs fundamentally between children and adults. Care is coordinated by pediatric emergency physicians, pediatric radiologists, and pediatric surgeons in children, and by emergency physicians, general or colorectal surgeons, and gastroenterologists in adults.
In children without perforation, peritonitis, or hemodynamic instability, non-surgical reduction is standard first-line treatment. An air (pneumatic) or contrast enema is performed under fluoroscopic or ultrasound guidance, using controlled pressure to push the telescoped segment back into position. Success rates are high—commonly reported in the range of 80 to 90 percent in favorable cases—and the procedure avoids an operation entirely in most children. Air enema is widely preferred over liquid contrast in many centers because of lower radiation dose and reduced peritoneal contamination if perforation occurs, though practice varies and both are effective. Perforation during reduction is uncommon but is the reason the procedure is performed with intravenous access established, fluid resuscitation underway, and surgical support available.
Repeat or delayed attempts at reduction are used in some centers when a first attempt partially succeeds and the child remains stable, and this approach can convert some initial failures into non-operative successes.
Surgery in children is reserved for failed enema reduction, perforation, peritonitis, hemodynamic instability, or an identified pathologic lead point. The operation involves manual reduction where possible and resection of any non-viable bowel or the lesion serving as the lead point. A laparoscopic approach is used in appropriately selected cases.
Recurrence after successful non-surgical reduction occurs in roughly 10 percent of children, most often within the first day or two but sometimes later. Recurrence is usually managed with repeat enema reduction rather than surgery. Multiple recurrences raise the likelihood of an underlying lead point and generally prompt further evaluation. Because early recurrence is common, families are given clear instructions on what to watch for after discharge.
In adults, the approach is essentially the opposite. Surgical resection is generally recommended rather than attempted reduction, for two reasons: an underlying lesion is usually present and may be malignant, and reducing the bowel before resection risks disseminating tumor cells and can mask the site of pathology. Resecting the involved segment without prior reduction allows definitive diagnosis and appropriate oncologic management. Reduction before resection may be considered in selected cases—for example, in young adults with a clearly benign cause, or where resection would sacrifice a large length of bowel—but this is an individualized surgical judgment. Incidentally discovered short-segment small bowel intussusception without obstruction or a lead point is generally observed rather than operated on.
Outcomes are generally very good when the diagnosis is made promptly. In children, early recognition and non-surgical reduction result in full recovery in the large majority, with no long-term consequences. Delay is the main determinant of poor outcome, since prolonged intussusception leads to bowel ischemia and the need for resection. In adults, prognosis depends primarily on the nature of the underlying lead point rather than on the intussusception itself, and evaluation continues after surgery according to what the pathology shows.
Prevention is limited, since most pediatric cases are idiopathic. Rotavirus vaccination remains recommended despite its small associated risk, as the overall benefit is clearly favorable. In adults, prevention overlaps with the prevention and early detection of the lesions that cause it, including age-appropriate colorectal cancer screening and appropriate surveillance in polyposis syndromes such as Peutz-Jeghers.
Care is coordinated by pediatric or adult surgical and radiology teams in the acute setting, and by pediatrics, gastroenterology, or oncology afterward depending on findings. Imaging, laboratory, and clinical findings are interpreted alongside the patient’s symptoms, examination, age, and broader clinical context rather than in isolation.
Patient and caregiver education plays an important role. For families, understanding that the classic triad is often incomplete, that unexplained lethargy in an infant can be a presenting sign, that most children avoid surgery entirely with enema reduction, that recurrence within the first days is possible and treatable, and which symptoms warrant immediate return all contribute to appropriate care. For adults, understanding why resection rather than reduction is recommended, and that the underlying lesion drives the subsequent plan, helps make sense of an unfamiliar diagnosis.
Red flag symptoms include repeated episodes of severe crampy abdominal pain in an infant with quiet or lethargic intervals between them, unexplained marked lethargy or unresponsiveness in a young child, persistent or bilious vomiting, blood or blood-and-mucus in the stool, a palpable abdominal mass, abdominal distension with inability to pass gas or stool, fever with a distended tender abdomen, signs of dehydration or shock (pallor, cold clammy skin, rapid heart rate, poor feeding, reduced wet diapers), and abdominal rigidity or severe tenderness. These warrant immediate emergency evaluation, as they may indicate obstruction, bowel ischemia, perforation, or shock.