Jejunal-ileal Atresia

Jejunal and ileal obstruction is typically caused by stenosis or atresia the lumen of one or more portions of the small intestine (bowel).

Small bowel atresias occur in 1.3-2.8/10,000 live births¹ and atresias of the jejunum or ilium are responsible for 39% of all intestinal atresias.² Atresia of the small bowel can occur at any point in the jejunum or in the ilium. Atresias of the small bowel are common in the proximal jejunum (31%) and distal ilium (36%).³ 6% of fetuses with small bowel obstruction have multiple atresias.⁴

Small bowel atresias are thought to be due to interruption of the blood supply to the intestine due to compression, intussusception, internal hernias, torsion or occlusion of the mesenteric vessels during embryonic life.⁵

Most fetuses with non-duodenal small bowel atresias have no additional abnormalities. In cases of isolated small bowel (jejunal and ilial) atresias, the risk for chromosomal abnormalities and nonchromosomal genetic syndromes is low, and evaluation for chromosomal abnormalities is therefore not necessary.⁶

The diagnosis of jejunal and ilial atresias can be challenging and not all cases of jejunal or ilial atesia will be identified prior to birth. In addition, prenatal ultrasound will not be able to determine the site(s) of the atresia with certainty.⁶ A recent metaanalysis of 640 recent cases of jejunoilial atresias found that detection rates are as high as 100% for proximal and 75% for distal atresias, however, only 50% were diagnosed prior to birth (range 0-100).⁷

Some small bowel atresias present with with echogenic bowel (EB) at the time of the second trimester anatomic survey, which is typically performed between 18-21 weeks of gestation. Echogenic bowel is defined as bowel as bright or brighter than bone. It is a nonspecific marker for bowel atresia and can be a transient finding in a normal fetus. Only 10% of fetuses with EB are later found to have either bowel atresia, chromosome abnormalities (commonly trisomy 21), viral infection, cystic fibrosis or IUGR.⁸ Patients carrying a fetus with echogenic bowel are offered chromosome, viral infection, cystic fibrosis testing at the time of diagnosis and follow-up scans to exclude IUGR and bowel obstructions.⁸

Small bowel atresias may not be evident until after 28-32 weeks of gestation but some are diagnosed in the late second trimester (9 Wax). Protocols which do not provide for routine third trimester screening may, therefore, have low detection rates, as patients may not be scanned at all in the third trimester or only for indications. The timing of the third trimester exam may matter; later scans may have higher detection rates. It is possible that cases with polyhydramnios may also have higher detection rates.

The most common third trimester findings associated with small bowel atresia are dilated loops of bowel with peristalsis.⁶ With serial scans, the maximum diameter of the bowel loops may progressively enlarge. In addition, the bowel walls may be echogenic and the loops of dilated bowel centrally located.⁶ There are several definitions of dilated bowel used in the literature⁷; in general, the normal bowel lumen should be less than 0.7cm.¹⁰ The diagnosis of multiple loops of dilated bowel with active hyperperistalsis makes the neonatal diagnosis more likely. Echogenic debris is often seen swirling inside the intestinal lumen as a result of peristalsis.⁶ Occasionally, fetuses are found to have abdominal cystic masses; 1/3-1/2 of these fetuses will subsequently be diagnosed with bowel atresia^11-12 and they should be reevaluated for bowel obstruction later in the pregnancy. With proximal (jejunal) atresias, polyhydramnios and a dilated fetal stomach may be seen but these are not consistent findings and may be seen only late in the pregnancy.⁹ Distal (ileal) atresias may perforate. A new finding of peritoneal calcifications, abdominal fluid (ascites) or the finding of a meconium pseudocyst suggests that perforation has occurred.⁶

Additional bowel abnormalities are frequently seen in neonates with jejunoilial atresia including: volvulus (5%), malrotation (13%), meconium ileus (12%) and meconium peritonitis (8%) (13). These abnormalities may not be identified in utero. There are typically no abnormalities outside the gastrointestinal tract.⁶ Babies with gastroschisis may have small bowel obstruction.

• Normal colon in third trimester (normal diameter up to 18 mm)
• Meconium ileus (may have identical findings)
• Hirschprung’s disease (may have identical findings)
• Volvulus (may have identical findings)
• Duodenal atresia
• Other cystic masses including ovarian cysts, enteric duplication cysts and mesenteric cysts can mimic intestinal atresia
• Malrotation of the bowel
• Colonic atresia
• Anal atresia
• Ureterectasis (enlarged ureters may be mistaken for dilated bowel loops

There is no prenatal treatment for bowel atresias. A sonographic diagnosis of bowel atresia will allow the parents time to adjust to the diagnosis and allow appropriate consultations with pediatric surgery and neonatal intensive care physicians. Prenatal diagnosis provides an opportunity for timely and appropriate evaluation of the neonate after delivery and prior to feeds. Prenatal findings and the time of diagnosis do not affect neonatal outcomes.⁹

The prognosis for small bowel obstruction depends on the extent of the small bowel atresia, the type of atresia, and the amount of normal bowel present at the time of surgery.¹⁴ After delivery, the pediatric surgeons typically categorize small bowel obstructions into four classes.⁵ In general, most neonates do well after surgery, however, they will remain in the NICU for prolonged periods of time for feeding assistance until bowel recovery.⁹ Unfortunately, the extent of bowel which will need to be resected and the number of anastomotic sites cannot be predicted prenatally.⁶ Some neonates will need a temporary colostomy with later surgery to reconnect the bowel. An occasional neonate will have poor outcome due to short gut syndrome or die from complications of prematurity or sepsis.^9&14

If echogenic bowel is identified and the initial workup is negative, followup ultrasound examinations are typically performed to evaluate the fetus for bowel atresias. Once a bowel obstruction is suspected, additional testing with growth scans should be performed to evaluate the fetus for IUGR which is more common with proximal obstructions. The fetal stomach, bowel diameter, presence of peristalsis, evidence of bowel rupture (ascites, calcifications), and fluid volume should also be evaluated. The rectum and anus should be evaluated to exclude anal atresia. BPP’s are typically performed in the third trimester. If a distal obstruction is suspected, cystic fibrosis (CF) screening should be considered. Vaginal delivery should be anticipated with caesarean reserved for patients with obstetric indications.

After delivery, the neonate should be evaluated by the pediatric team prior to feeding. A nasogastric tube is placed and IV is begun for fluid and electrolyte management. The baby is evaluated by pediatric surgery and the neonatal intensive care unit team and additional testing performed to confirm the diagnosis. Screening for cystic fibrosis is typically performed if it was not done in the antenatal period.

Genetic counselling is suggested for the couple. While recurrence risks are generally low, familial cases have been identified. Recurrence risk may depend on the type of atresia found at the time of surgery. Recurrence risk is increased with type IIIb (apple-peel deformity)^14,16, Type IV ^17,18, and hereditary multiple atresia syndrome.¹⁸ If cystic fibrosis is identified, there is a 25% recurrence risk for CF.

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