Case #10 Discussion:

The differential diagnosis of bilious vomiting in an 18 mo.-old includes midgut volvulus, small bowel obstruction and intussusception. Non-bilious vomiting at this age is most often due to viral gastroenteritis or gastro-esophageal reflux disease (GERD). Abdominal cramping and bloody stools suggest intussesception.

Intussusception is the telescoping of a part of the bowel into another distal segment. About 90% are ileocolic and 10% ileoileal or colocolic in origin. The peak incidence of occurrence is 3 mos. to 3 years of age. The vast majority (95%) of intussusceptions in this age group are idiopathic, meaning there is no definable structural defect that leads to the condition. Theories as to the cause of idiopathic cases in the young include lymphoid hyperplasia, hyperperistalsis due to viral infection and disproportionate size of the ileum compared to the ileocecal valve. Definable structural abnormalities or lead points are more commonly found in children older than 3 yrs. of age and may include Meckel's diverticulum, submucosal hemorrhage, lymphoma, lymphosarcoma and polyps. In neonates, bowel duplication may serve as a lead point and in older children and adults, a normal or pathologic appendix may serve as a lead point.

Intussusception is more common in males than females (ratio 3:2) and most commonly occurs in the winter and spring. The sequence of events leading to the symptomatology is thought to result from invagination causing venous compression that leads to bowel swelling, which then compromises arterial supply. The resulting ischemia may then cause bowel hemorrhage, infarction, necrosis and perforation. The most common presenting signs and symptoms include: colicky abdominal pain (94%), vomiting--bilious or non-bilious (91%), bloody "currant jelly" stools (66%) and a palpable abdominal mass usually in the RUQ (59%). Less commonly, URI symptoms (20%), diarrhea (10%), lethargy, fever and signs of cardiovascular compromise are present.

The initial radiologic evaluation of a child with a concerning abdominal complaint is usually a supine abdominal X-ray. Intussusception on a plain X-ray may appear as a soft tissue mass, abnormal gas pattern or small bowel obstruction (SBO). US has been shown to have a very high negative predictive value (approaching 100%). The gold-standard is the contrast enema which typically shows an intraluminal mass.

Enemas often serve a therapeutic role as well. Barium, water-soluble contrast, or air enemas can successfully reduce the intussusception in 80-98% of patients. The three contrast media seem to be equally effective and result in the same complication rates, but there are advantages and disadvantages to each. Barium provides good mucosal detail, but can cause serious peritonitis in the few who perforate. Water-soluble agents show less detail of the lesion, but are less hazardous if perforation occurs. Air contrast provides good visibility of the lesion and is less hazardous when perforation occurs, but does not provide good detail of the mucosa. The main contraindication to radiographic reduction is clinical instability, as indicated by signs and symptoms of hypovolemic shock, peritonitis and/or perforation. While the presence of a lead point may not complicate radiographic reduction, most causes of lead points require surgical intervention. Some advocate radiographic reduction even if a lead point is identified so as to facilitate surgical intervention. If the intussusception is not successfully reduced, surgical reduction is necessary. 5-10% of cases recur.