Radiography
Ileal atresia. Upright radiograph of the abdomen demonstrates many dilated loops of bowel and air-fluid levels.
Ileal atresia. Same patient as in Image 2 in Multimedia. Contrast enema study demonstrates microcolon with abrupt cut-off of contrast material filling of the ileum. Image shows no filling of dilated bowel proximal to the obstruction and a lack of filling defects in the small bowel.
Ileal atresia. Contrast enema study demonstrates a small, unused colon with abrupt truncation of the column of contrast agent in the distal ileum.
Meconium ileus. Main differential consideration. Plain radiograph of the abdomen demonstrates dilated loops of bowel with no rectal air and with a soap-bubble appearance in the right lower quadrant.
Cystic meconium peritonitis. Plain radiograph of the abdomen shows multiple air-filled loops of bowel, some dilated, and a large, rounded structure with calcified wall in the mid abdomen.
Meconium ileus. Same patient as in Image 5 in Multimedia. Contrast enema study demonstrates microcolon with reflux of contrast agent into small bowel of a caliber similar to that of the colon. Round, tubular filling defects that represent inspissated meconium are demonstrated in the small bowel.
Findings
Plain radiographic findings include a dilated stomach (if no nasogastric [NG] suction was used), numerous loops of dilated bowel, multiple air-fluid levels proximal to the point of obstruction, and absent gas distal to the obstruction. A dilated loop of bowel may be observed immediately proximal to the site of atresia; this is a common finding with atresias in general. This loop may be filled with fluid and resemble a mass. Ultrasonography may be helpful to show that this is fluid-filled bowel.12
Meconium peritonitis can occur when an atresia or other obstruction leads to an in utero bowel perforation. It is most commonly seen in the setting of jejunal or ileal atresia. Calcifications around bowel and in the peritoneum are evident in meconium peritonitis. These calcifications can be focal, cystic or generalized. In the male patient, they may extend into the scrotum by means of a patent processus vaginalis.
Contrast enema study is indicated when plain radiographs demonstrate a distal obstruction. In ileal atresia, the colon is diffusely small (<1 cm, ie, microcolon). Filling of the distal small bowel with contrast agent is abruptly cut off, because material cannot reflux past the atresia into the dilated ileum proximal to the obstruction. It is this abrupt truncation of the contrast column that allows differentiation of ileal atresia, a surgical lesion, from meconium ileus, a medical lesion when uncomplicated.
Both meconium ileus and ileal atresia cause distal obstruction and microcolon. In contrast to ileal atresia, meconium ileus classically shows few, if any, air-fluid levels. Plain radiographs may show a characteristic bubbly appearance in the right lower quadrant, which represents inspissated meconium mixed with air.
A definitive diagnosis can usually be made by performing a contrast enema study. In meconium ileus, the contrast agent can be refluxed past the obstructing, inspissated meconium into the dilated proximal ileum. The inspissated meconium may appear as round or tubular filling defects in the contrast material–filled small bowel. Furthermore, contact with the contrast material usually softens and loosens the inspissated meconium, allowing it to pass. This feature makes contrast enema study the preferred initial therapy for meconium ileus, whereas ileal atresia always requires surgical repair.
Technique
It is important to reflux contrast material as far into the small bowel as is necessary to allow differentiation of these 2 conditions and to allow the material to contact all of the inspissated meconium.
Choice of contrast agent
With regard to the type of contrast agent, dilute, water-soluble contrast material is preferred for the diagnostic enema study in the neonate.
The rationale for using water-soluble, iodinated contrast instead of barium involves multiple factors. The first is the potential for spilling contrast material into the peritoneal cavity in the clinical setting of necrosis and perforation of the atretic bowel. On occasion, the perforation is not demonstrated on the initial plain image. Barium in the peritoneal cavity is not absorbed and may induce the development of adhesions. Even if no perforation is present, water-soluble contrast agent in the colon is preferable to barium if the patient needs immediate surgery after the examination.
Furthermore, 2 entities in the differential diagnosis of low intestinal obstruction, meconium ileus and functional immaturity of the colon, often clinically improve after an enema study performed with water-soluble contrast. A follow-up therapeutic contrast enema procedure increases the likelihood of successful treatment of meconium ileus. Therapeutic enema is more likely to be successful if the preceding diagnostic enema was performed with water-soluble contrast material rather than barium.
Another concern is that barium can become inspissated in the colon and may be difficult to evacuate. Finally, the improved depiction of mucosal detail with barium is not important in the newborn.
The iodinated contrast used for the enema study should be diluted to be nearly isosmolar to serum, yet it should be dense (opaque) enough to be adequately visualized. Use of undiluted, high-osmolality contrast agents in infants can cause fluid shifts from the intravascular space to the lumen of the colon and result in life-threatening serum electrolyte imbalances.
High- and low-osmolality agents provide adequate contrast if iodine concentrations greater than 180 mg Iodine per milliliter are used.13 Normal serum osmolality is 285 mOsm/kg of water. High-osmolality, water-soluble agents include sodium and meglumine salts of diatrizoate and iothalamate, and these range in osmolality from 400-2000 mOsm/kg of water. If diluted to be nearly isosmolar to serum, these agents may be used instead of relatively expensive, nonionic, low-osmolality contrast agents. The low-osmolality, water-soluble agents range in osmolality from 290 (isosmolar) to 844 mOsm/kg of water.
The osmolality of most commercially available contrast agents is specified on the product insert. If the package insert does not state the osmolarity of the product, a particular dilution is recommended, for example, 1:3-5 for agents with high osmolality. As an alternative, this information can be found in Appendix A Contrast Media Specifications of the Manual on Contrast Media from the American College of Radiology.14
Degree of Confidence
The degree of confidence in plain radiographic findings is high for determining the presence of high versus low obstruction. For low obstruction, further imaging is necessary to localize the site and nature of the obstruction.
Contrast enema study offers a high degree of confidence in the diagnosis if good reflux of contrast agent into the small bowel can be achieved.
Magnetic Resonance Imaging
Findings
Ultrasonography
Cystic meconium peritonitis. Same patient as in Image 7 in Multimedia. Sonogram shows rounded, echogenic near-surface and posterior acoustic shadowing. Distal ileal perforation was discovered at surgery.
Findings
Ultrasonography is valuable in the diagnosis of in utero bowel obstruction, as the dilated bowel is filled with fluid rather than air. The number of dilated loops indicates proximal versus distal obstruction, and findings may be specific in some causes of proximal obstruction, such as the double bubble of duodenal atresia.15,16
In the postnatal period, air is introduced into the gut, making sonography less useful than before, particularly in distal obstruction, where a great deal of air absorbs the ultrasound beam.
If the results of the contrast enema study are equivocal, sonography may help distinguish ileal atresia from ultrameconium ileus in select cases. Meconium ileus is characterized by echogenic material within dilated loops of small bowel, whereas ileal atresia results in intestinal dilatation with anechoic fluid.17
Sonography may elucidate associated findings, such as meconium peritonitis. Fibrotic tissue with calcifications has an echogenic appearance with posterior acoustic shadowing. When peritonitis is generalized throughout the peritoneum, a snowstorm appearance may be demonstrated.
Although they typically do not cause obstruction in the newborn period, enteric duplication cysts are well evaluated with ultrasound. The wall of the cyst is characterized by a layered appearance with an inner echogenic layer of mucosa, surrounded by a hypoechoic layer of muscularis propria, the so-called gut signature. Peristalsis may also be observed in the cyst.
Degree of Confidence
In utero, the finding large number of dilated fluid-filled loops has a high positive predictive value, but this finding does not differentiate one cause from another.
More on Ileal Atresia |
| Overview: Ileal Atresia |
 Imaging: Ileal Atresia |
| Follow-up: Ileal Atresia |
| Multimedia: Ileal Atresia |
| References |
| Further Reading |
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References
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ACR. American College of Radiology Manual on Contrast Media. 5th ed. Reston, Va: American College of Radiology;. 2004.
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Further Reading
Related eMedicine topics
Small Intestinal Atresia and Stenosis
Atresia, Stenosis, and Other Obstruction of the Colon
Obstruction, Small Bowel
Small-Bowel Obstruction (from Radiology)
Small-Bowel Obstruction (from Pediatrics: General Medicine)
Clinical guidelines
American College of Radiology. Manual on Contrast Media. ACR Practice Guideline. Version 6. 2008. Available at http://www.acr.org/SecondaryMainMenuCategories/quality_safety/contrast_manual.aspx.
Accessed February 25, 2009.
Practice Management Guidelines for Small Bowel Obstruction
Suspected Small Bowel Obstruction
Clinical trials
Gastrografin Use in Small Bowel Obstruction Caused by Adherences (GUSBOCA)
Bioresorbable Membrane to Reduce Postoperative Small Bowel Obstruction
Keywords
ileal atresia, atresia of the ileum, neonatal intestinal obstruction, ileal stenosis, small intestine atresia, small intestine stenosis, atresia of the small intestine, stenosis of the small intestine, jejunal atresia, small bowel atresia, small bowel stenosis, small-bowel atresia, small-bowel stenosis, meconium peritonitis, apple peel atresia, apple-peel atresia, Christmas tree atresia, Christmas-tree atresia
