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Not movin’: Pediatric bowel obstruction
Case presentation
A 2-year-old male with a medical history of Hirschsprung disease requiring colectomy and ileo-anal pullthrough presents with multiple episodes of nonbilious emesis and no stool output over the past 24 hours. The mother states that she has noted that the child has had increased abdominal girth over the past 48 hours and has become fussy. He has had decreased oral intake. There has been no fever, cough, congestion, or diarrhea.
Shortly after birth, he underwent colectomy and ileostomy (which was taken down several months prior to his acute presentation). He has a chronic dysmotility disorder and is followed closely by Pediatric Gastroenterology. The mother has tried rectal dilatation and Miralax at home, per the child’s usual regimen when there is decreased stool output, without success. She has also noted no passage of flatus.
Physical examination reveals an interactive, non–toxic appearing, but visibly uncomfortable, child. He is afebrile. He has a heart rate of 130 beats per minute, respiratory rate of 24 breaths per minute, blood pressure of 93/54 mm Hg, and pulse oximetry of 99% on room air. His examination is remarkable for a moderately distended abdomen that does not appear to be tender. There is no organomegaly. Digital rectal examination results in an explosion of liquid, brown, nonbloody stool.
Imaging considerations
The location of the suspected obstruction will help the clinician determine which imaging modality to employ.
Plain radiography
This modality is often a first-line test and is rapidly available, requiring minimal exposure to ionizing radiation. Plain radiography can assist in the identification of the level of obstruction and can help guide the clinician in choosing more advanced imaging modalities, if indicated. , Bowel gas patterns can be associated with various pathologies: the “double bubble” sign of duodenal atresia, the “triple bubble” sign of proximal jejunal atresia, various abnormal patterns associated with meconium ileus, multiple air-filled loops of bowel with a lack of rectal gas in the infant with Hirschsprung disease, distended stomach in some infants with pyloric stenosis, radio-opaque foreign bodies, and a soft tissue mass effect on the right and lack of colonic air in some infants with intussusception. Perforation and free air can also be demonstrated. This is a primary value of plain abdominal radiography, but plain radiographs may vary and may even be normal in some pathologies, such as malrotation and volvulus.
Ultrasound
Ultrasound is a first-line imaging modality for several causes of intestinal obstruction in pediatric patients, such as pyloric stenosis, intussusception, and pediatric appendicitis. , The usefulness of ultrasound to detect malrotation has been investigated. In this technique, the relationship of the superior mesenteric artery (SMA) and the superior mesenteric vein (SMV) is evaluated. The SMA is normally to the left of the SMV. When the SMV is to the left of the SMA, the relationship of the vessels is inverted. It has been suggested that if this relationship is abnormal, the patient should undergo an upper gastrointestinal series (UGI) to confirm the presence or absence of malrotation. A study examining this relationship reported a false-positive rate of 21% (abnormal ultrasound and normal UGI) and a false-negative rate of 2% (normal ultrasound and abnormal UGI). , Another series found an abnormal relationship between these structures to have a sensitivity and specificity of 67% to 100% and 75% to 83% for malrotaion. Therefore, SMA/SMV inversion as a solitary finding is not highly sensitive or specific for malrotation. Additional sonographic signs that improve the value of ultrasound for malrotation include the “whirlpool sign,” where the mesentery and mesenteric vessels are wrapped around the SMA and SMV, and evaluation of whether the transverse duodenum is in a normal retroperitoneal position. When these two additional signs are evaluated in addition to SMA/SMV inversion, the sensitivity of ultrasound for malrotation is markedly improved, with one study showing a sensitivity of 100% and a specificity of over 97% in the detection of malrotation. However, such an examination requires significant pediatric sonographic imaging expertise to perform and interpret and would find greatest utility in a facility with dedicated pediatric sonography.
Upper gastrointestinal series
This is the diagnostic test of choice in patients with suspected malrotation with or without volvulus as a cause of intestinal obstruction. False-positive and false-negative test results do occur, reported to be up to 15% and up to 6%, respectively, , so proper technique and expertise in imaging interpretation are essential to provide meaningful and accurate results.
Computed tomography (CT)
While not a typical first-line imaging test in children with suspected bowel obstruction, CT is useful at detecting such pathology. The pediatric literature is not as prolific compared to the adult literature investigating the use of CT in the diagnosis of intestinal obstruction. However, one study looking at small bowel obstruction reported a sensitivity of 87% and a specificity of 86% for detecting small bowel obstruction in pediatric patients (especially those over the age of 2 years); these percentages included patients with adynamic ileus, since this may be difficult to distinguish from bowel obstruction on CT. CT is also useful in detecting the level of obstruction (comparable to adult studies) in most patients (86%) but was not as useful in determining the cause of obstruction (54%). CT may be employed as a secondary test if other imaging modalities are equivocal or there is concern for a complex intra-abdominal process.
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