AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Background

Approximately 95% of intestinal obstructions diagnosed in the first 2 weeks of life are due to atresia and/or stenosis of small intestine (Grosfeld, 1970). Atresia represents complete luminal obstruction of a hollow viscus, and stenosis involves partial occlusion. Atresia is more common than stenosis. At birth, complete obstruction is present with atresia, whereas various degrees of stenosis manifest with mild-to-severe sequelae. Ileal atresia represents 50% of small-intestinal atresias (Hernanz-Schulman, 1999). Ileal atresia is more common than jejunal atresia.

Pathophysiology

Ischemia is the cause for jejunal and ileal atresia and stenosis. The etiology of ischemia is most commonly a primary vascular accident and less commonly in utero obstruction, such as volvulus. Malrotation and internal hernia have also been noted. Because the bowel contents are sterile in the fetus, the necrotic tissue is resorbed or converted into fibrous bands.

The succus entericus, which forms the meconium, is composed of secretions from the stomach and small bowel, desquamated cells, and secreted fluid and bile. Exposure to succus entericus expands the size of the colon from its fetal size. The timing and location of atresia determines whether the succus entericus enters the colon during its development.

In proximal atresias, the colon is normal or nearly normal in size, because adequate succus entericus reaches the colon from small bowel distal to the obstruction. On the other hand, distal atresias are usually associated with an unused colon or microcolon less than 1 cm in diameter. When the ischemic event occurs later in gestation, the colon may be normal in caliber, even if the obstruction is distal.

Small-bowel atresia, meconium ileus, volvulus, intussusception, and idiopathic causes can be complicated by perforation resulting in meconium peritonitis. In utero perforation of bowel may allow spill of meconium into the peritoneal space. Fibrosis ensues, and peritoneal calcification may occur. Calcifications may be irregular, linear, round, or generalized in appearance. Intraluminal calcifications may also occur in cases of severe obstruction.

Meconium peritonitis occurs in 5.2% of cases (de Lorimier, 1969).

Frequency

United States

The incidence of atresia of the small bowel ranges from 1 case in 332 live births (Walker, 2000) to 1 case in 5000 live births (Okada, 2002). About 15% of ileal atresias occur proximally, and 30% occur distally (Belknap, 1994).

Mortality/Morbidity

In general, early diagnosis of ileal atresia reduces the mortality rate.

• The overall survival rate for ileal atresia is 75.3%, whereas that for multiple atresias is 16% (de Lorimier, 1969).
• Martin and Zerella (1976) described the survival rate for each subtype as follows: type I, 85%; type II, 66%; type III (or type IV under the current classification), 29%; and type IV (or type IIIB under the current classification), 57%.

Race

• No specific racial predilection is known.
• Multiple atresias of the small bowel with luminal calcification occur in people of French Canadian descent, with an autosomal recessive inheritance pattern. The mortality rate for this condition is high, and it is associated with dilatation of the biliary duct.
• Nonhereditary forms of multiple intestinal atresias with intraluminal calcifications also exist.

Sex

There is no sex predilection for this disease.

Age

Most ileal atresias are diagnosed in the first 24 hours of life. The age at presentation is 1-30 days (de Lorimier, 1969). Prematurity of the neonate is related to the severity of the subtype of atresia (Martin, 1976). (See Anatomy below.)

Anatomy

Ileal atresia occurs in 4 main types with subtypes (see Image 1). Type I is characterized by a thin diaphragm that occludes the lumen. In type II, 2 blind ends are connected with a fibrous cord of atretic bowel. In type IIIA, 2 blind ends terminate with a V-shaped mesenteric defect; this is the most common type. Type IIIB, apple-peel or Christmas-tree atresia, involves a large, V-shaped mesenteric defect in which the blind-ended bowel distal to the atresia is wrapped around its blood supply. Type IV is defined as multiple atresias.

In Christmas-tree or apple-peel atresia, the proximal superior mesenteric artery is occluded. The distal small intestine spirals around its vascular supply of collaterals from the ileocolic artery. This is associated with an absent distal superior mesenteric artery, shortening of the small intestine distal to the atresia, and absent dorsal mesentery. Prematurity, malrotation, and short gut occurs in most patients (Seashore, 1987). An autosomal recessive inheritance pattern is suggested.

Jejunal and ileal atresias uncommonly coexist and are multiple; therefore, the entire small bowel must be examined at surgery.

Clinical Details

Polyhydramnios occurs in one fourth of cases and is more common in proximal jejunal atresia than in distal ileal atresia (Stringer, 1989).

The clinical manifestations of ileal atresia appear in the first 24 hours of life. Symptoms of stenosis are less severe and may occur later. The most common presenting symptom is bilious vomiting, which may be associated with abdominal distension or an inability to pass meconium.

In one quarter of cases, a probable etiology is identified at the time of surgery. These causes include malrotation, volvulus, gastroschisis, or intussusception.

Extra-GI anomalies are rare and occur in less than 7% of patients (de Lorimier, 1969).

Preferred Examination

In the newborn with suspected intestinal obstruction, the preferred initial examination is plain radiography of the abdomen. This examination allows for the differentiation of high (proximal) and low (distal) obstruction, and the results dictate the next appropriate step in management.

In infants, small bowel is impossible to distinguish from large bowel, but newborns are unique in that they are swallowing air for the first time. If bowel obstruction is complete, no air is present distal to the obstruction. Therefore, the abdominal radiograph is like an upper-GI series with air as the contrast medium. The number of loops of dilated, air-filled bowel differentiates high from low obstruction.

If only a few loops of dilated bowel are seen, a high obstruction is present. The plain radiograph is often diagnostic, as with the double-bubble sign of duodenal atresia. All causes of high intestinal obstruction in the newborn are surgical; therefore, further imaging is not usually indicated. If surgery is to be delayed or if the plain radiograph is normal, an upper-GI series must be performed to exclude malrotation and/or midgut volvulus. This condition requires immediate surgery and is the diagnosis most likely to produce a normal radiograph in a neonate.

If the abdominal radiograph shows many dilated loops of bowel, a low obstruction is present. The differential diagnosis includes incarcerated inguinal or umbilical hernia, ileal atresia, meconium ileus, ileal duplication cyst, colonic atresia, functional immaturity of the colon, Hirschsprung disease, and imperforate anus. Hernia and imperforate anus are diagnosed on the basis of clinical examination. Otherwise, a contrast enema study is indicated to differentiate surgical from medical causes of distal bowel obstruction in the newborn.

Limitations of Techniques

Plain radiographs in the newborn are useful in determining the level of obstruction, but atresias are occasionally multiple, and the plain radiographs demonstrate only the most proximal obstruction. In addition, dilated loops of bowel filled with fluid may go undetected or may be mistaken for a mass. Cross-table radiographs showing air-fluid levels are often helpful in such instances. Also, radiographs may be normal in cases of malrotation and intermittent midgut volvulus.

The upper-GI series may add no information to a diagnostic plain radiograph showing a pathognomonic finding, such as the double bubble of duodenal atresia.

If the referring physician requests both an upper-GI series to exclude midgut volvulus and a contrast enema study, one examination can interfere with the other. If there is an indication for both, the upper-GI series should be performed first. Contrast should be administered through an enteric tube. The enteric tube is then used to aspirate as much of the contrast agent as possible after the duodenal jejunal junction is evaluated.

Contrast enema is useful in demonstrating microcolon, but if contrast agent is inadequately refluxed into the distal small bowel, meconium ileus may be mistaken for ileal atresia; this mistaken finding may lead to unnecessary surgery.

Ultrasonography can demonstrate dilated fluid-filled loops of bowel, but is of limited utility in the neonatal period, because it does not show the site of obstruction. It may be helpful for specific limited purposes, such as differentiating a dilated fluid-filled loop of bowel from a mass, diagnosing enteric duplication cyst or helping to differentiate meconium ileus from ileal atresia (see Ultrasound).

CT and MRI have no role in the diagnosis of ileal atresia.

DIFFERENTIALS

Section 3 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Other Problems to be Considered

Colonic atresia
Imperforate anus
Incarcerated inguinal or umbilical hernia
Ileal duplication cyst
Functional immaturity of the colon

RADIOGRAPH

Section 4 of 10  

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• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

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.

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 (Cohen, 1987). 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.

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.

CT SCAN

Section 5 of 10  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Findings

CT has no role in the diagnosis of ileal atresia.

MRI

Section 6 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Findings

MRI has no role in the diagnosis of ileal atresia.

ULTRASOUND

Section 7 of 10  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

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.

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 (Neal, 1997).

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.

INTERVENTION

Section 8 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Special Concerns

• Use of barium or of undiluted, hypertonic water-soluble contrast agents in the performance of a diagnostic enema study can cause untoward complications. Barium should be avoided in the newborn for a number of reasons.
• • The main reason is the potential for spilling contrast material into the peritoneal cavity. Bowel adjacent to the atretic bowel is at risk of perforation and can be necrotic. On occasion, initial plain images do not demonstrate the perforation. Barium in the peritoneal cavity is not absorbed. Ensuing inflammatory response can lead to formation of granulomata and adhesions.
  • In addition, barium can become inspissated in the colon, leading to obstruction. Patients at risk are those with Hirschsprung disease, cystic fibrosis, ileus, and blind loops of bowel.
  • Use of undiluted, high-osmolality contrast agents in infants can cause fluid shifts resulting in life-threatening serum electrolyte imbalances.
• It is important to minimize radiation exposure in children.
• • Important steps to include effective immobilization and limiting field size to the area of interest.
  • Gonadal shielding should be used whenever possible.
  • During fluoroscopic procedures, examination time should be kept to a minimum. Pulsed fluoroscopy further decreases radiation exposure to the patient.

MULTIMEDIA

Section 9 of 10  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

Media file 1:  Ileal atresia occurs in 4 main types with subtypes. Type I is characterized by a thin diaphragm that occludes the lumen. In type II, 2 blind ends are connected with a fibrous cord of atretic bowel. In type IIIA, 2 blind ends terminate with a V-shaped mesenteric defect; this is the most common type. Type IIIB, apple-peel or Christmas-tree atresia, involves a large, V-shaped mesenteric defect in which the blind-ended bowel distal to the atresia is wrapped around its collateral blood supply. Type IV is defined as multiple atresias.
	View Full Size Image
Media type:  Image

Media file 2:  Ileal atresia. Upright radiograph of the abdomen demonstrates many dilated loops of bowel and air-fluid levels.
	View Full Size Image
Media type:  X-RAY

Media file 3:  Ileal atresia. Same patient as in Image 2. 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.
	View Full Size Image
Media type:  X-RAY

Media file 4:  Ileal atresia. Contrast enema study demonstrates a small, unused colon with abrupt truncation of the column of contrast agent in the distal ileum.
	View Full Size Image
Media type:  X-RAY

Media file 5:  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.
	View Full Size Image
Media type:  X-RAY

Media file 6:  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.
	View Full Size Image
Media type:  CT

Media file 7:  Meconium ileus. Same patient as in Image 5. 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.
	View Full Size Image
Media type:  X-RAY

Media file 8:  Cystic meconium peritonitis. Same patient as in Image 7. Sonogram shows rounded, echogenic near-surface and posterior acoustic shadowing. Distal ileal perforation was discovered at surgery.
	View Full Size Image
Media type:  CT

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Intervention
• Multimedia
• References

• ACR. American College of Radiology Manual on Contrast Media. 5th ed. Reston, Va: American College of Radiology;. 2004.
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• Neal MR, Seibert JJ, Vanderzalm T, Wagner CW. Neonatal ultrasonography to distinguish between meconium ileus and ileal atresia. J Ultrasound Med. Apr 1997;16(4):263-6; quiz 267-8. [Medline].
• Okada PJ, Hicks B. Neonatal surgical emergencies. Clin Peditr Emerg Med. 2002;3(1):3-13.
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• Stringer DA. Congenital and developmental anomalies of the small bowel. In: Stringer DA, Babyn PS. Pediatric Gastrointestinal Imaging. London: BC Decker;. 1989: 255-62.
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• Walker WA. Congenital anomalies. In: Walker WA, Hamilton JR, Watkins JB, Durie PR, Walker-Smith JA, eds. Pediatric gastrointestinal disease. 3rd ed. London: BC Decker;. 2000: 556-61.
• Weitzman JJ, Vanderhoof RS. Jejunal atresia with agenesis of the dorsal mesentery. With "Christmas tree" deformity of the small intestine. Am J Surg. Mar 1966;111(3):443-9. [Medline].

Article Last Updated: May 3, 2006