| Discussion: |
Intussusception is a process in which a segment of intestine invaginates into the adjoining intestinal lumen, causing a bowel obstruction. Intussusception presents in 2 variants, ie, idiopathic intussusception, which usually starts at the ileocolic junction and affects infants and toddlers, and enteroenteral intussusception (jejunojejunal, jejunoileal, ileoileal), which occurs in older patients. The latter is associated with special medical situations (eg, Henoch-Schönlein purpura [HSP], cystic fibrosis, hematologic dyscrasias) and can occur in the postoperative period.
Pathophysiology: The pathogenesis of intussusception is believed to be secondary to an imbalance in the longitudinal forces along the intestinal wall. This imbalance can be caused by a mass acting as a lead point or by a disorganized pattern of peristalsis (eg, an ileus in the postoperative period). As a result of the imbalance, an area of the intestinal wall invaginates into the lumen, with the rest of the intestine following. The invaginating portion of the intestine (ie, intussusceptum) completely invaginates into the receiving portion of the intestine (ie, intussuscipiens). This process continues and more proximal areas follow, allowing the intussusceptum to proceed along the lumen of the intussuscipiens.
If the mesentery of the intussusceptum is lax and progression is rapid, the intussusceptum can proceed to the distal colon or sigmoid and even prolapse out of the anus. The mesentery of the intussusceptum is invaginated with the intestine, leading to the classic pathophysiologic process of any bowel obstruction.
Early in this process, lymphatic return is impeded; then, with the rise in the pressure within the wall of the intussusceptum, venous drainage is impaired. Finally, the pressure reaches a point at which arterial inflow is inhibited, and infarction ensues. The mucosa is most sensitive to ischemia because it is farthest away from the arterial supply. Ischemic mucosa sloughs off, which initially leads to the heme-positive stools and then the classic "currant jelly stool" (a mixture of sloughed mucosa, blood, and mucus). If untreated, the process progresses to transmural gangrene and perforation of the leading edge of the intussusceptum.
Race: No significant difference in the incidence of intussusception is reported between races.
Sex: Most series report a slight preponderance of males, with a male-to-female ratio of approximately 3:2.
Causes: In most infants and toddlers with intussusception, etiology is unclear. This group is believed to have idiopathic intussusception. One theory about the etiology of idiopathic intussusception is that it occurs because of an enlarged Peyer patch; this hypothesis is derived from 3 observations, ie, (1) often, the illness is preceded by an upper respiratory infection, (2) the ileocolic region has the highest concentration of lymph nodes in the mesentery, and (3) enlarged lymph nodes often are observed in patients who require surgery. Whether the enlarged Peyer patch is a reaction to the intussusception or a cause of it is unclear.
- Two thirds of children with intussusception are younger than 1 year; most commonly, intussusception occurs in infants aged 5-10 months. Although extremely rare, intussusception has been reported in the neonatal period.
- Intussusception can account for as many as 25% of abdominal surgical emergencies in children younger than 5 years, exceeding the incidence of appendicitis.
- Intussusception is the most common cause of intestinal obstruction in patients aged 5 months to 3 years.
- From a clinical perspective, using a cutoff age of 3 years is helpful for dividing patients with intussusception into 2 groups. Patients aged 5 months to 3 years who have intussusception rarely have a lead point (ie, idiopathic intussusception), and they usually are responsive to nonoperative reduction. Older children and adults more often have a surgical lead point to the intussusception and require operative reduction.
- In approximately 2-12% of children with intussusception, a surgical lead point is found. Occurrence of surgical lead points increases with age and indicates that the probability of nonoperative reduction is highly unlikely. Examples of lead points are as follows:
- Enlarged mesenteric lymph node
- Benign or malignant tumors of the mesentery or of the intestine, including lymphoma, polyps, and hamartomas associated with Peutz-Jeghers syndrome
- Mesenteric or duplication cysts
- Submucosal hematomas, which can occur in patients with HSP and coagulation dyscrasias
- Ectopic pancreatic and gastric rests
- Inverted appendiceal stumps
- Sutures and staples along an anastomosis
- Other theories have implicated a viral etiology; however, no theory has proven to be reliable.
Imaging Studies: Plain radiograph findings may be normal early in the course of intussusception.
- Familial occurrence of intussusception has been reported in a few cases. Intussusception in dizygotic twins has been reported; however, these reports are extremely rare.
- As the disease progresses, earliest radiographic evidence includes an absence of air in the right lower and upper quadrants and a right upper quadrant soft tissue density present in 25-60% of patients.
- These findings are followed by an obvious pattern of small bowel obstruction, with small bowel dilatation and air-fluid levels in the small bowel only. If the distention is generalized and the air-fluid levels also are present in the colon, the findings more likely represent acute gastroenteritis than intussusception.
- A left lateral decubitus view is also helpful. If the view exhibits air in the cecum, the presence of ileocecal intussusception is highly unlikely.
- Ultrasonography is a noninvasive modality that can aid in making the diagnosis of intussusception.
- Hallmarks of ultrasonography include depiction of the intussusceptum and its mesentery within the intussuscipiens (target and pseudokidney signs)
- Ultrasonography is highly operator dependent; therefore, interpret results with caution.
- Computed tomography (CT) scan also has been proposed to be useful making the diagnosis of intussusception; however, CT findings are unreliable, and use of CT carries the risks associated with intravenous contrast administration, radiation exposure, and sedation.
- The traditional and most reliable way to make the diagnosis of intussusception in children is to obtain a contrast enema (either barium or air).
- Contrast enema is quick and reliable and has the potential to be therapeutic.
- Exercise caution when performing contrast enema in patients older than 3 years because most patients older than 3 years have a surgical lead point in the small bowel, and the diagnostic and therapeutic yield of the enema is lower in these patients.
- When performing a therapeutic enema, the recommended pressure of air insufflation should not exceed 120 cm of water. When using barium or water-soluble contrast, the column of contrast should not exceed 100 cm above the level of the buttocks. An attempt is not considered successful until the reducing agent, whether air, barium, or water-soluble contrast, is observed refluxing back into the terminal ileum. Otherwise, the intussusception can remain at the ileocecal region and can resume its progression.
- The value of repeated attempts at nonoperative reduction, if the first attempt is unsuccessful, has not been determined. Some clinicians recommend taking the patient to surgical care if the first attempt fails, and other clinicians advocate 1 or 2 subsequent attempts within a few minutes to a few hours after the first attempt. Delay between the reduction attempts may place the patient in the "window" of spontaneous resolution, which has been reported with an incidence of 5-6%. In addition, the first attempt can reduce the intussusception partially, making the intussusceptum less edematous with improved venous drainage.
- Delay in performing surgery because of additional attempts at nonoperative reduction has been demonstrated to have no adverse effects on the rates of success of operative reduction and morbidity in the patient.
- When therapeutic enema is successful, the results are immediate and extremely gratifying. The infant falls asleep almost immediately, and the obstruction is relieved, allowing the resumption of a normal diet. A short period of overnight observation usually is warranted before discharge.
- The recurrence rate of intussusception after nonoperative reduction is usually less than 10% but has been reported as high as 21%. Most intussusceptions recur within 72 hours of the initial event; however, recurrences have been reported up to 36 months later. More than one recurrence suggests the presence of a lead point. A recurrence usually is heralded by the onset of the same symptoms as appeared during the initial event. Provide similar treatment for a recurrence unless the suggestion of a lead point is very strong; in which case, contemplate surgical exploration.