Pediatric Gastrointestinal Radiology

1

What are the most common causes of small bowel obstruction in a child?

AAIIMM is a mnemonic that makes it easy to remember the causes:

• A = A dhesions, usually post-surgical.

• A = A ppendicitis.

• I = I ntussusception.

• I = I ncarcerated inguinal hernia.

• M = M alrotation with volvulus or bands.

• M = M iscellaneous, such as Meckel's diverticulum or intestinal duplication.

2

What is intussusception?

Intussusception is a condition in which a proximal portion of the bowel (intussusceptum) telescopes into the adjacent distal bowel (intussuscipiens). When the inner loop and its mesentery become impacted, a small bowel obstruction results.

3

What causes intussusception?

In most cases in children, the cause of intussusception is idiopathic. In less than 5% of cases, the intussusception contains a lead point, such as a polyp, a Meckel's diverticulum, or hypertrophic lymphatic tissue. Most intussusceptions are ileocolic in origin.

4

Describe the clinical signs of intussusception.

The classic clinical triad of intussusception is intermittent colicky abdominal pain, currant jelly stools, and a palpable abdominal mass. However, less than 50% of patients actually present with these symptoms. Children often cry and are very irritable during bouts of abdominal pain, and then become drowsy and lethargic. Vomiting and fever may also occur. Intussusception is most common in children 3 months to 4 years of age, with a peak incidence occurring at 3 to 9 months of age, and occurs more commonly in boys.

5

How is intussusception diagnosed with imaging?

The most accurate imaging technique for the diagnosis of intussusception is ultrasonography (US). The characteristic US appearance is an easily detectable mass measuring in the range of 3 to 5 cm. In the transverse plane, the mass has a “target” appearance (which contains echogenic fat), while the “pseudokidney” sign is how it will appear in the longitudinal plane. A contrast enema (utilizing water-soluble contrast material or air) with fluoroscopy can also be used to diagnose intussusception. Although conventional radiographs have been used in the past to diagnose intussusception via occasional detection of a soft tissue mass in the right upper quadrant with associated lack of a large amount of bowel gas, studies have shown poor interobserver agreement and a predictive value of only approximately 50%.

6

How is an intussusception treated?

An intussusception is treated by air or hydrostatic enema using barium or water-soluble contrast material (the latter is favored) under fluoroscopic guidance ( Figure 87-1 ). Some radiologists will attempt to perform the reduction under US guidance during a water-soluble contrast enema, with final confirmation of reduction with a single overhead frontal radiograph obtained on the fluoroscopy table. The advantages of the air enema are that it is quicker, less messy, and easier to perform and delivers less radiation to the patient. The only contraindications to enema reduction of intussusception are presence of pneumoperitoneum or peritonitis. The air enema can generate pressures of up to 120 to 140 mm Hg in order to reduce the intussusceptions, but pressure above this is to be avoided in order to prevent iatrogenic perforation.

7

How can one tell that an intussusception has been successfully reduced?

If a successful air reduction has been performed, fluid with air bubbles should be seen passing through the ileocecal valve into the terminal ileum. If a successful reduction with contrast material has been performed, contrast material must reflux into multiple loops of small bowel. If reflux into the small bowel is not seen, the intussusception may not have been completely reduced, and a distal lead point may have been overlooked. A “pseudomass” may remain in the region of the edematous ileocecal valve despite successful reduction, not to be mistaken for a residual intussusception.

8

Describe the “double bubble” sign, and name the conditions in which it is found.

The “double bubble” sign is found on radiographs and represents an air-filled or fluid-filled distended stomach and duodenal bulb ( Figure 87-2 ). It may be seen in bowel malrotation, duodenal atresia, and jejunal atresia but is usually the sine qua non of duodenal atresia.

9

What is malrotation of the intestines?

Malrotation of the intestines is a misnomer because it is really nonrotation or incomplete rotation of the bowel. To understand malrotation, one must first consider normal embryologic rotation of the intestines. During normal embryologic development in the first trimester, the midgut leaves the abdominal cavity, travels into the umbilicus (umbilical cord), and subsequently returns to the abdominal cavity. As the intestines return, the proximal and distal parts of the midgut rotate around the superior mesenteric artery axis by 270 degrees in a counterclockwise direction. The ligament of Treitz (duodenojejunal junction) lands in the left upper quadrant, and the cecum comes to rest in the right lower quadrant. In malrotation, this intestinal rotation and fixation occur abnormally. If normal rotation does not occur, the cecum is not anchored in the right lower quadrant and may be in the midline or in the upper abdomen, and the small bowel is not anchored in the left upper quadrant and may lie entirely in the right hemi-abdomen.

10

What are Ladd's bands?

Ladd's bands are dense peritoneal bands that develop as an attempt to affix the bowel to the abdominal wall in bowel malrotation. These may extend from the malpositioned cecum across the duodenum to the posterolateral abdomen and porta hepatis in either incomplete rotation or nonrotation, and they can cause extrinsic duodenal obstruction.