Intussusception is a common cause of childhood intestinal obstruction, occurring more frequently in white children aged 6 months to 2 years and in more males than in females (3:1-2). [1, 2] When this condition occurs in neonates and in children older than 2 years, there is a high incidence of associated bowel abnormality that serves as an initiating lead point for intussusception (about 5% of patients are found to have a lead point). In addition, intussusception is known to occur with greater frequency in children who have undergone recent abdominal surgery, either intraperitoneal or retroperitoneal operations. It is thought that early adhesions or focal edema of the bowel wall create a lead point for the intussusception.
Invagination of a bowel segment (usually, the small bowel) into the lumen of the more distal bowel (usually, the colon) occurs. The invaginated segment (intussusceptum) is carried distally by peristalsis. Mesentery and vessels become involved with the intraluminal loop and are squeezed within the engulfing segment (intussuscipiens). Almost all occurrences are acute, and bowel obstruction is often the presenting sign of intussusception (see the image below).
A loop of bowel infolds (and inverts) more distally into the lumen of the bowel and is then carried distally by peristalsis. Approximately 90% of intussusceptions are ileocolic, in which the terminal ileum is carried through the ileocecal valve into the colon; it may reach the rectum. Idiopathic intussusceptions usually lack an identifiable lead point and occur in children aged 6 months to 2 years. Lymphoid hyperplasia or hypertrophic lymph nodes have been postulated but not proven. Lead points in nonidiopathic intussusception may include the following:
Lymphoma of bowel
Leukemia involving bowel
Henoch-Schonlein purpura with intramural hemorrhage
Cystic fibrosis with inspissated bowel content
Postoperative complication following retroperitoneal surgery
Post abdominal trauma
Peutz-Jeghers syndrome appendix (normal or appendicitis)
Recent rotavirus immunization 
In some countries, history and physical findings are sufficient criteria for undertaking reduction procedures for intussusception. However, abdominal radiography and ultrasonography may be useful studies, and in some institutions, reduction of the intussusception takes place under ultrasonographic guidance with fluid or air. [4, 5, 6, 7]
Abdominal radiography may used to search for dilated small bowel and an absence of gas in the region of the cecum (see the image below). In some cases, a mass impression within the colonic gas indicates an intraluminal mass created by the intussuscepting loop.
Transverse ultrasonograms show a mass with a swirled appearance of alternating sonolucent and hyperechoic bowel wall of the loop-within-a-loop. On longitudinal ultrasonograms, the intussuscipiens and the intussusceptum have the appearance of a submarine sandwich. There appear to be multiple layers, which represent the walls of the intussuscepted bowel loops, as seen in the image below.
Limitation of techniques
Intussusception may not be apparent on plain-film abdominal radiography. Radiographs may appear indeterminate or normal; therefore, the presence of an unremarkable abdominal radiograph should not be the basis for excluding a diagnosis of intussusception.
Ultrasonographic examination is almost always positive, although overlying loops of air-containing bowel may obscure intussusception (see the following image).
Differential diagnosis and other problems to be considered
The differential diagnosis should include appendicitis and cecal volvulus. Other conditions that should be considered include inflammatory bowel disease, appendicitis with or without perforation, incarcerated inguinal hernia, internal hernia, appendicitis, Henoch-Schonlein purpura, hemolytic uremic syndrome, small bowel obstruction, cecal/sigmoid volvulus, and abdominal wall hernia.
Prolonged intussusception may result in bowel necrosis and/or perforation. Once the patient is stabilized, reduction procedures should be initiated immediately; radiographic examination and physical examination should be performed to ensure that neither free air nor peritonitis is present. It should be ascertained by physical examination that no peritonitis is present.
Unless perforation, peritonitis, or Henoch-Schonlein purpura is present, radiologic reduction should be attempted. The success rate is 50-85%, depending on factors such as the length of time of the intussusception and degree of edema of the loop and ileocecal valve. Reduction is still possible, although more difficult, in intussusceptions that have been in place for longer than 48 hours. In patients older than 2 years, it should be assumed that intussusception has a lead point etiology; in such cases, further investigation should be undertaken. [8, 9, 10]
Spontaneous reduction has been reported, but it is unusual and surgery is advised when radiologic reduction is unsuccessful. Despite positive results from reduction through the use of imaging techniques, reduction or re-intussusception may be unsuccessful, necessitating surgery. Rarely, complications from reduction with imaging techniques (perforation) require emergency surgery. The use of air, gas, or water-soluble contrast to reduce the intussusception decreases potential complications. [11, 12]
In the current method of air reduction, room air is introduced through a rectal catheter and is taped well in place. A manometer is attached to a Y-connector to monitor pressure in the colon. Pressure should never exceed 110 mm Hg. The air pressure on the intussusception usually forces the inverted bowel back through the ileocecal valve and into its proper position. When reduction occurs, the observed pressure falls precipitously.
Contrast reduction was widely used until the current decade. A large rectal tube is taped firmly in place, and dilute water-soluble contrast is introduced slowly by gravity drip into the rectum; hydrostatic pressure is used to reduce the intussusception. The fluid is placed a maximum of 3 feet above the level of the radiography table. No more than 3 attempts at reduction are undertaken, and the column is pressed against the intussusception mass no longer than 3 minutes at each attempt. Visualization of the small bowel usually indicates that intussusception has been reduced. The following rules need to be observed:
The fluid level should be maintained at no more than 3 feet above the patient.
Palpation of the abdomen should be avoided during reduction.
Pressure should be maintained no longer than 3 minutes against a nonmoving intussusception.
Reduction may proceed at an uneven rate, and it may slow at various locations; this is particularly true at the ileocecal valve, which is swollen and often resists passage of the intussusception (see the images below). To ensure reduction, contrast should be observed entering the ileum. Once contrast enters the ileum, it often proceeds quickly through the ileum. Vomiting is a frequent side effect of reduction.
The appendix usually fills before the ileum and should not be confused with the ileal reflux of contrast. If there is a problem with reduction across the ileocecal valve, the patient should be allowed to evacuate, and the ileum should then be refilled; this relaxes the valve and allows for better control on refilling. A swollen ileocecal valve may appear unreduced; therefore, identifying air or contrast material in the ileum is important (see the following image below).
One should be aware of conditions that lead to intussusception and that also are predictive of perforation (eg, Henoch-Schonlein purpura). Contrast enema procedures should be avoided in patients with these conditions.
Radiographic findings may be normal. However, usually, a pattern of small bowel obstruction with absence of gas in the right colon is visible. An intraluminal colonic filling defect may indicate intussusceptum, and intraluminal blood may create a speckled pattern of gas and colonic material.
A careful search should be made for intraperitoneal free air; the presence of free air is a contraindication for reduction by enema, because the presence of free air indicates that the bowel is already perforated (see the images below).
The appearance of small bowel obstruction in conjunction with characteristic clinical findings almost always indicates intussusception, as does the appearance of a gasless cecum and/or an intraluminal bowel mass. Unless otherwise indicated, the diagnosis should be confirmed with an air or barium enema.
Any abnormality that has an appearance like that of small bowel obstruction mimics intussusception, because findings often are nonspecific. In addition, appendicitis may have an "empty cecum" appearance that looks like intussusception, whereas inflammatory bowel disease may involve the cecum and appear like intussusception. Severe edema of the bowel wall, as found in shigellosis, Salmonella infection, or enterohemorrhagic Escherichia coli infection, may appear like intussusception.
Computed tomography (CT) scanning is not normally indicated in child intussusception; however, if a lead point (eg, lymphoma) is suspected, CT scanning may be helpful. See the following image. Volvulus and some intraperitoneal masses (eg, cystic teratoma) mimic intussusception.
Transverse sonography of the intussusception mass reveals a swirled pattern of alternating hyperechogenicity and hypoechogenicity, representing the alternating layers of mucosa, muscularis, and serosa. Some centers use ultrasonography to monitor reduction of the intussusception with fluid introduced via the rectum. On ultrasonography, intussusception has a characteristic appearance; it is usually not mistaken for other bowel abnormalities. [13, 14] On longitudinal sonography, alternating loops of bowel and a loop-within-loop have a sandwichlike appearance (see the image below).