Intestinal Obstruction in the Newborn Workup

Updated: Mar 17, 2016
  • Author: James G Glasser, MD, MA, FACS; Chief Editor: Ted Rosenkrantz, MD  more...
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Workup

Approach Considerations

Imaging is a mainstay of the diagnosis of intra-abdominal pathology and should be readily performed in an infant with suspected intestinal obstruction. Noninvasive techniques, such as plain radiography and ultrasonography, can be performed at the bedside and can yield valuable information. A Gastrografin (diatrizoate) enema may be both diagnostic and therapeutic; however, clinicians not only must ensure the infant is well hydrated prior to the enema study but also must avoid excess hydrostatic pressure so as not to cause intestinal perforation.

Imperforate anus may occur as part of the VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, and limb) association of congenital anomalies. Anorectal malformations are considered midline defects and require investigation for other midline anomalies. Ultrasonography and radiography of the heart, central nervous system (CNS), kidneys, and the sacral vertebrae and radii are recommended.

Computed tomography (CT) scans may be useful in the diagnosis of malrotation/volvulus. Normally, the superior mesenteric artery lies to the left of the superior mesenteric vein. Reversal of this spatial relationship suggests malrotation with midgut volvulus.

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Ultrasonography

Polyhydramnios is present in 50% of fetuses with duodenal obstruction. The stomach and proximal duodenum are fluid-filled and dilated. The image on fetal ultrasonography is similar to that of the “double-bubble sign” observed on radiography of the infant after birth (ie, air fills the dilated stomach and duodenum).

Prenatal ultrasonography may detect small bowel obstruction due to jejunal atresia (which may also lead to polyhydramnios). This may be detected on prenatal ultrasonography.

Fetal ultrasonography may not be able to detect distal intestinal obstruction. Dilated loops of small bowel may be mistakenly identified as colon as parturition approaches.

One of the complications of meconium ileus is in utero perforation; the extruded meconium is contained by adjacent loops of intestine, creating a pseudocyst. This causes intense inflammation of the overlying abdominal wall, termed “meconium peritonitis.” Distintincive ultrasonographic features of meconium peritonitis include meconium pseudocyst, echogenic mass, abdominal calcifications, ascites, polyhydramnios, and dilated bowel or intestinal obstruction. [19]  In other instances, the perforation may seal after releasing only a small amount of meconium. Extraluminal meconium calcifies, and these scattered calcifications may be seen with fetal ultrasonography and abdominal radiography.

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Radiography

Duodenal atresia

Plain x-rays of the abdomen show the classic “double-bubble sign.” Air is an excellent contrast medium and may be introduced into the baby’s stomach through a nasogastric tube, if duodenal obstruction is suspected. Incomplete duodenal obstruction mandates urgent radiographic imaging, laparotomy, or both to differentiate duodenal atresia from malrotation/volvulus.

Malrotation with volvulus

When a baby, in whom midgut volvulus is suspected, presents with bilious vomiting, obtain an upper gastrointestinal (GI) series. [20, 21] Findings that corroborate this diagnosis include incomplete obstruction of the duodenum caused Ladd bands or volvulus. The ligament of Treitz may be located to the right of the vertebral column, directly below the pylorus.

If the presentation is abdominal distention and tenderness and, possibly, hematochezia, a barium enema is more definitive, because it differentiates malrotation/volvulus from Hirschsprung enterocolitis. Radiographic signs of malrotation include absence of the splenic and hepatic flexures, and the cecum is in the right upper quadrant. With midgut volvulus, there is obstruction to the flow of contrast medium through the distal colon.

See the images below.

Malrotation volvulus. Note the partial duodenal ob Malrotation volvulus. Note the partial duodenal obstruction. The distal duodenum does not cross the midline (over the vertebral column) and the "curly Q" twist.
Duodenal atresia. Note the double-bubble sign and Duodenal atresia. Note the double-bubble sign and narrowing in the second portion of the duodenum. There is partial obstruction, the duodenum does cross the midline, and there is no twist.

Jejunal atresia

Plain radiography of the abdomen reveals distention of the stomach and small bowel proximal to the obstruction. In 12% of newborns with jejunoileal atresia, intra-abdominal calcifications, which represent extraluminal meconium, are observed on plain radiography. This association occurs because interruption of blood flow to the atretic bowel is followed by sterile necrosis and perforation of the intestine with extrusion of meconium.

Occasionally, in proximal atresias with large mesenteric defects, the distal bowel obtains its blood supply by retrograde flow from the ileocecal vessels. The tiny, unused intestine spirals around these vessels, simulating an “apple peel” or “Christmas tree” appearance. The tip of the “Christmas tree” (the proximal end of the preserved distal intestine) may twist and obstruct its rather precarious blood supply, adding urgency to the evaluation and surgical correction of this condition, because the length of the intestine is already shortened by the atresia.

Distal obstruction

Typically, plain radiography reveals multiple dilated loops of intestine, air fluid levels, and absence of air in the rectum. A diatrizoate (Gastrografin) enema is indicated and demonstrates “microcolon.” In patients with meconium plug, the diatrizoate enema is both diagnostic and therapeutic.

Meconium ileus

Bowel loops with varying diameters are seen on plain radiography, as well as a “soap bubble” or “ground glass” appearance from the sticky, inspissated meconium. Scattered calcifications suggest in utero perforation.

Meconium plug syndrome

A contrast enema should be performed in all infants with distal intestinal obstruction. It is diagnostic of meconium plug syndrome—a normal colon laden with meconium filling defects—as well as therapeutic, facilitating evacuation of a meconium plug. Hirschsprung disease may be associated with meconium plug syndrome in 4% of patients; therefore, some clinicians perform a rectal biopsy in patients presenting with meconium plug syndrome.

Gastrografin enema. Note the tiny, unused colon an Gastrografin enema. Note the tiny, unused colon and the dilated (by swallowed air) proximal, obstructed intestine.

Hirschsprung disease

Hirschsprung disease may be diagnosed by finding a “transition zone” on contrast radiography, which is defined by an abrupt change in diameter between the narrow aganglionic rectum and distal colon, and the dilated, more proximal, normally innervated bowel. Failure to evacuate contrast medium within 24 hours of the enema is another finding characteristic of Hirschsprung disease.

Imperforate anus

A cross-table lateral x-ray, with the baby in prone “jack-knife” position, reveals the position of the rectum relative to the levator muscle complex. This study helps clinicians to determine whether an anoplasty or a colostomy is appropriate as the initial operative procedure. This radiologic study should be performed 12-24 hours after birth to allow for swallowed air to reach the rectum.

Newborns with a low imperforate anus have a fistula to the skin; in those with a high imperforate anus, the fistula ends in the genitourinary system (the bladder, urethra, or vagina). Low lesions may be primarily repaired by perineal anoplasty. In newborns with high imperforate anus, a temporary colostomy is the safer option.

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Other Tests

Anal manometry

Anal manometry is utilized in patients with Hirschsprung disease. A positive study demonstrates failure of the rectum to relax following inflation of the balloon; however, the study is impossible to perform in uncooperative children.

Rectal biopsy

If the contrast study suggests Hirschsprung disease, it should be followed by a confirmatory rectal biopsy. Suction rectal biopsy may be performed at the bedside with a specially designed instrument inserted through the baby’s anus. Suction is applied through a side hole, and a knife amputates a small piece of rectal mucosa and muscularis mucosa. The specimen is examined for ganglion cells, which, if present, effectively eliminates Hirschsprung disease from further diagnostic consideration.

Acetylcholinesterase staining of the submucosa may reveal abnormal hypertrophic nerve fibers characteristic of Hirschsprung disease. False positives may occur, [22] because an absence of ganglion cells may simply reflect inadequacy of the tissue sample; hence, full-thickness rectal biopsy should be performed to corroborate the negative finding of “absent ganglion cells,” before concluding that the diagnosis of Hirschsprung disease is definitive.

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