Pediatric Small Bowel Obstruction Workup

Updated: Oct 27, 2020
  • Author: Pranit Chotai, MD; Chief Editor: Carmen Cuffari, MD  more...
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Workup

Laboratory Studies

After a careful history and physical examination are complete, the following laboratory tests may be useful in patients with small bowel obstruction:

  • Basic metabolic panel

  • Complete blood cell (CBC) count

  • Urinalysis and urine culture

  • Blood culture

  • Arterial blood gas (ABG) level

  • Stool for occult blood

A leukocytosis with a left shift may develop late in the disease process when bowel has been compromised; alternatively, this finding could suggest another disease process such as appendicitis or sepsis that is mimicking some signs of small bowel obstruction. Thrombocytopenia often accompanies severe necrotizing enterocolitis; a more than 30% drop in platelet count is associated with increased morbidity and mortality, as well as length of hospital stay. [37]

The basic metabolic panel is a helpful marker of a child’s level of volume depletion, a common finding in children with small bowel obstruction.

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Imaging Studies

Many obstructive processes in children can be identified with plain radiographs. A flat decubitus and upright radiograph of the abdomen can reveal dilated small bowel loops and air-fluid levels that are produced by the layering of air and intestinal contents. Absent colonic or rectal gas may also be present in a complete obstruction. The pattern of bowel gas on plain radiography can help to differentiate between proximal and distal bowel obstructions. In lieu of an upright radiograph, a left lateral decubitus film can also be obtained to demonstrate air-fluid levels or, in the case of perforation, to identify free intraperitoneal air.

Ultrasonography can identify many intestinal abnormalities causing obstruction, including tumors, mesenteric cysts, and intussusceptions. Contrast studies such as an upper gastrointestinal (GI) series or contrast enema can also be used to diagnose an obstruction and determine the obstruction location. Contrast studies may also help reveal whether the obstruction is intrinsic or extrinsic to the bowel.

Abdominal computed tomography (CT) scanning is occasionally necessary to identify the specific cause of a small bowel obstruction, in particular in the evaluation of chronic partial obstructions and to rule out other etiologies that may mimic small bowel obstruction.

Finally, magnetic resonance imaging (MRI) can also be used to evaluate small bowel obstructive processes. For example, small bowel strictures in patients with inflammatory bowel disease are often diagnosed using magnetic resonance enterography (MRE).

Additional details regarding the imaging for frequently encountered diagnoses are provided below.

Intussusception

Plain abdominal radiography can be useful in the diagnosis of intussusception. [38, 39] X-rays can suggest a soft-tissue mass projecting toward the right upper quadrant or reveal the intussusceptum projecting into the air-filled colon. Abdominal radiography may also reveal scattered air-fluid levels that suggest partial obstruction.

The diagnosis is typically confirmed with ultrasonography, which reveals a "target" sign that corresponds to the echogenic appearance of the intussusceptum in the intussuscipiens. The reliability and accuracy of ultrasonography may help avoid unnecessary radiologic studies or surgical intervention. [40] See the images below.

Pediatric Small Bowel Obstruction. This sonogram r Pediatric Small Bowel Obstruction. This sonogram reveals intussusception in a 9-month-old male patient.
Pediatric Small Bowel Obstruction. A barium enema Pediatric Small Bowel Obstruction. A barium enema study on a 1-year-old male patient depicts an ileocolic intussusception.
Pediatric Small Bowel Obstruction. This barium ene Pediatric Small Bowel Obstruction. This barium enema study reveals a coil spring appearance caused by the tracking of barium around the lumen of the edematous intestine in intussusception.

Abdominal CT scanning and MRI are usually unnecessary to make the diagnosis of intussusception. Contrast radiography can be diagnostic as well as therapeutic (see Treatment).

Incarcerated hernia

Incarcerated hernias are diagnosed clinically, and no imaging studies are required. Air-fluid levels are often visible on plain radiography when obtained. The bowel may be visible within the inguinal canal and scrotum. Ultrasonography may reveal the incarcerated viscera in the inguinal canal or umbilical ring and can be useful in difficult cases (see the image below).

Pediatric Small Bowel Obstruction. This image reve Pediatric Small Bowel Obstruction. This image reveals small bowel obstruction caused by an incarcerated inguinal hernia in a 2-month-old infant with bilateral inguinal hernias as well as an umbilical hernia.

Malrotation of the bowel with midgut volvulus

Volvulus is typically identified using plain radiography, an upper GI series, or CT scanning. [41]

Plain abdominal radiography may reveal air-fluid levels, especially in the stomach and duodenum, or the abdomen may appear gasless on abdominal plain radiography. Distended loops of small bowel are only occasionally visible because the point of obstruction is proximal.

An upper GI series is the classic study to diagnose malrotation with or without volvulus. The duodenum usually has a "C" shape, and the duodenojejunal junction is localized to the left of the midline. [42] In malrotation, the duodenum lacks this normal shape and does not cross the midline. Duodenal obstructions can also be identified. The classic patterns of volvulus are the "bird beak," in cases involving complete duodenal obstruction, or the "corkscrew,” in cases involving incomplete obstruction.

Malrotation can also be identified on ultrasonograms and CT scans. Ultrasonographic findings suggestive of malrotation include the following [43] :

  • Third part of the duodenum not in the normal retromesenteric position (ie, located between the superior mesenteric artery [SMA] and the aorta in the retroperitoneal space)

  • Abnormal position of the superior mesenteric vein (either anterior or to the left of the SMA [the superior mesenteric vein is normally located to the right of the SMA])

  • The "whirlpool" sign of volvulus caused by the vessels twisting around the base of the mesenteric pedicle

  • Dilated duodenum (suggesting duodenal obstruction by Ladd bands)

Finally, contrast enema findings may provide indirect evidence of malrotation by revealing an ectopically placed right colon and cecum. However, a high or mobile cecum is common in many asymptomatic patients, and a significant number of patients with malrotation will have a normal contrast enema.

Postoperative adhesive small bowel obstruction

Supine and upright abdominal radiography reveals dilated, gas-filled loops of small intestine with air-fluid levels. If the diagnosis is in question or if there is concern for compromised bowel that would preclude a trial of nonoperative management, a CT scan can be obtained to provide additional data for decision making.

Duplication cysts

Enteric duplication cysts are increasingly detected prenatally. [44] Plain radiography may reveal a soft-tissue mass within the abdomen that displaces the adjacent bowel. An upper GI contrast series may reveal stenosis or extrinsic compression from the mass. Technetium scanning can be used to image duplications that contain ectopic gastric mucosa. For most abdominal duplications, ultrasonography is more expedient and provides greater detail than does conventional contrast radiography. Although typically unnecessary, enteric duplications can also be visualized on CT scan or MRI.

Necrotizing enterocolitis

Abdominal radiography initially reveals multiple gas-filled loops of intestine and air-fluid levels. Straightening of the bowel wall and bowel wall thickening with intramural air suggest mural edema (railroad sign). A gasless abdomen, a fixed bowel loop, or a ground-glass appearance, which suggests free intraperitoneal fluid, is occasionally encountered. [45] Pneumatosis intestinalis is the radiographic hallmark; its presence indicates gas in the bowel wall. Portal venous gas is an ominous sign suggesting more advanced disease, and pneumoperitoneum indicates a bowel perforation. Pneumatosis intestinalis and portal venous gas can also be detected using ultrasonography; color Doppler ultrasonography may be a more accurate method of diagnosing bowel necrosis than plain abdominal radiography. [46]

See the images below.

Pediatric Small Bowel Obstruction. The plain abdom Pediatric Small Bowel Obstruction. The plain abdominal film of a premature baby born at 28 weeks of gestation reveals necrotizing enterocolitis. Note the "railroad sign" (pneumatosis intestinalis) in the hepatic flexure and "soap bubbles" in the descending colon.
Pediatric Small Bowel Obstruction. A plain abdomin Pediatric Small Bowel Obstruction. A plain abdominal film of a premature baby girl with necrotizing enterocolitis is shown. Note the air in the biliary tree and the grossly dilated bowel.

Mesocolic hernia

An upper GI study with small bowel follow-through may support the diagnosis of mesocolic hernia. However, abdominal CT scanning is the diagnostic imaging study of choice. [35]

Jejunoileal atresia and stenosis

Plain radiography demonstrates dilated intestinal loops and air-fluid levels proximal to the level of obstruction. In many cases, plain radiography is sufficient to make the diagnosis. A contrast enema may also be helpful to obtain, however, especially when plain radiography suggests a more distal bowel obstruction and colonic obstruction must be ruled out. A contrast enema can distinguish between small and large bowel distention, determine the presence or absence of a microcolon, and locate the position of the cecum with regard to possible abnormalities of intestinal rotation and fixation. Even when plain radiography more clearly demonstrates a small intestinal atresia, a preoperative contrast enema is often desired to obviate the need for a full examination of the colon intraoperatively (when it has already been shown to be normal on contrast enema). An upper GI series can reveal the level of obstruction with grossly distended proximal bowel. However, contrast aspiration is a significant risk, and this study is not routinely necessary. See the image below.

Pediatric Small Bowel Obstruction. An upper gastro Pediatric Small Bowel Obstruction. An upper gastrointestinal contrast study demonstrates a jejunal atresia with a proximal dilated atretic bowel and lack of passage of contrast material into the distal small bowel.

Duodenal atresia and stenosis

Abdominal radiography usually confirms a duodenal atresia diagnosis by showing a dilated stomach and proximal duodenum (ie, the double-bubble sign), with little to no air present in the distal GI tract. With this classic appearance, no further studies are necessary.

The double-bubble sign characteristic of duodenal obstruction can also be seen in cases of annular pancreas. If the child has vomited or has been decompressed using a nasogastric (NG) tube prior to abdominal radiography, the stomach and duodenum may be collapsed, making the correct diagnosis difficult. In such cases, a small amount of air (ie, 10-15 mL) may be injected into the stomach through the NG tube, and radiography may be repeated.

An upper GI series is rarely necessary in neonates and creates unnecessary risk of contrast aspiration from vomiting. Upper GI studies are more useful in the later diagnosis of a duodenal web or stenosis. See the images below.

Pediatric Small Bowel Obstruction. The plain abdom Pediatric Small Bowel Obstruction. The plain abdominal film on a 3-day-old newborn depicts the classic double-bubble sign for duodenal atresia.
Pediatric Small Bowel Obstruction. This radiograph Pediatric Small Bowel Obstruction. This radiograph depicts the double-bubble sign characteristic of duodenal atresia.
Pediatric Small Bowel Obstruction. This contrast-e Pediatric Small Bowel Obstruction. This contrast-enhanced upper gastrointestinal film shows a duodenal atresia in a 2-day-old newborn.

Meconium disease

Abdominal radiographic studies reveal multiple air-fluid levels consistent with a distal (usually at the terminal ileum) small bowel obstruction. The presence of calcifications throughout the peritoneum suggests a prenatal perforation and meconium peritonitis or meconium pseudocyst. The inspissated meconium often has a ground-glass appearance on radiography. A "soap-bubble" image in the right lower quadrant is characteristic. A contrast enema is diagnostic and, in many cases, therapeutic for meconium ileus. The contrast enema reveals a microcolon (nonused colon) and varying degrees of obstruction of refluxing contrast material into the small intestine caused by meconium pellets in the terminal ileum.

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