Small bowel atresia is a congenital complete obstruction of the small intestine and is one of the most common causes of intestinal obstruction in the neonatal period. Incidence is approximately 1/5000-10000 live births. Duodenal atresia is the most common type with a strong association with Down syndrome (30%). Jejunoileal atresia develops as a result of an in-utero vascular event (mesenteric ischemia), and the spiral-shaped bowel loss (apple peel atresia) is its characteristic form. Polyhydramnios and dilated bowel loops on prenatal ultrasound suggest the diagnosis. On postnatal plain radiograph, the 'double bubble sign' is pathognomonic for duodenal atresia. Treatment is surgical resection and anastomosis.
Age Range
0-1
Peak Age
-
Gender
Equal
Prevalence
Rare
Two distinct pathogenetic mechanisms are described in small bowel atresia. Duodenal atresia results from failure of recanalization of the duodenal lumen at 8-10 weeks of fetal development — during the embryonic period, the duodenum temporarily forms a solid cord and normally the lumen reopens through vacuolization; failure of this process leads to complete or incomplete (duodenal web) obstruction. Jejunoileal atresia results from ischemic necrosis and resorption of a bowel segment due to in-utero mesenteric vascular event (thrombosis, volvulus, intussusception). In apple peel (Type IIIb) atresia, proximal jejunal atresia + absence of distal SMA branches → remaining ileum winds spirally while being fed retrogradely from the marginal artery of SMA. Dilation and hypertrophy of the proximal segment are secondary changes due to downstream obstruction — this creates the proximal dilation + distal microcolon pattern on imaging.
Appearance of two separate 'bubbles' formed by the dilated stomach and proximal duodenum on prenatal US or postnatal plain radiograph. Pathognomonic for duodenal atresia. Chromosome analysis is recommended due to Down syndrome association.
Two separate fluid-filled structures in the fetal abdomen on prenatal ultrasound — dilated stomach and proximal duodenum ('double bubble sign'). This finding is generally visible from the 2nd trimester. Polyhydramnios (in 50% of cases) accompanies. Associated anomalies (cardiac defects, annular pancreas) should be investigated. Trisomy 21 screening is recommended.
Report Sentence
Double bubble sign (dilated stomach and proximal duodenum) in the fetal abdomen on prenatal ultrasound is observed, consistent with duodenal atresia.
Two large air-fluid levels in the abdomen on postnatal plain radiograph or CT — stomach and dilated proximal duodenum. Absence of distal bowel gas indicates complete atresia, while presence of small amounts of distal gas may be consistent with duodenal web (incomplete obstruction) or annular pancreas. CT provides additional information in evaluating associated anomalies (malrotation, annular pancreas, cardiac).
Report Sentence
Double bubble sign and absence of distal bowel gas on postnatal radiograph are observed, consistent with complete duodenal atresia.
Several prominently dilated bowel loops and small-caliber colon (microcolon) in the distal bowel on CT in jejunoileal atresia. The number of dilated loops depends on the level of atresia — in proximal jejunal atresia 1-3 dilated loops, in distal ileal atresia numerous dilated loops. Microcolon develops due to non-use of the colon failing to develop — lumen diameter may be <1 cm. In apple peel atresia, spirally wound small bowel loops create a characteristic appearance on CT.
Report Sentence
Several dilated small bowel loops and distal microcolon are observed, consistent with jejunoileal atresia.
Dilated small bowel loops appear with high signal on T2-weighted images in fetal MRI — loops filled with meconium and amniotic fluid are hyperintense. MRI is superior to US as a complementary modality for evaluating the level of atresia, distal bowel and colon status, and associated anomalies. Apple peel morphology can be better demonstrated on MRI.
Report Sentence
T2 hyperintense dilated small bowel loops and small-caliber structures in the distal bowel on fetal MRI are observed, consistent with small bowel atresia.
Polyhydramnios on prenatal ultrasound (amniotic fluid index >24 cm or deepest pocket >8 cm) — more prominent in high-level atresias. Polyhydramnios is present in 50% of duodenal atresia cases. Fluid accumulates due to impaired intestinal absorption despite fetal swallowing of amniotic fluid. Polyhydramnios increases the risk of preterm delivery.
Report Sentence
Polyhydramnios and dilated fetal bowel loops are observed, consistent with congenital intestinal obstruction (small bowel atresia).
Microcolon with contrast enema (or rectal contrast on CT) — small-caliber, unused colon lumen. Colon diameter is generally <1 cm and contrast agent cannot easily advance. The level to which contrast agent advances estimates the level of atresia. Contrast reaching the ileocecal valve level suggests ileal atresia, contrast not reaching the cecum suggests more proximal atresia.
Report Sentence
Microcolon on contrast enema is observed, consistent with unused colon and proximal intestinal atresia.
Criteria
Congenital obstruction of the duodenum — due to recanalization failure
Distinct Features
Type I: intraluminal membrane (web), Type II: two ends connected by fibrous cord, Type III: complete gap. 30% Down syndrome association. Double bubble sign pathognomonic.
Criteria
Congenital obstruction of jejunum or ileum — due to in-utero vascular event
Distinct Features
Number of dilated loops depends on atresia level. Distal microcolon. Down syndrome association lower than duodenal.
Criteria
Proximal jejunal atresia + absence of distal SMA branches → spiral ileum
Distinct Features
Remaining ileum winds spirally while being fed retrogradely from marginal artery — 'apple peel' appearance. High risk of short bowel syndrome. Familial transmission has been reported.
Distinguishing Feature
Adhesive obstruction is an acquired condition with previous surgical history; atresia is congenital and presents in the neonatal period
Distinguishing Feature
In intussusception, 'target/ring' appearance and 'meniscus sign' are present; in atresia, complete obstruction and absence of distal gas
Distinguishing Feature
Neonatal ischemia (NEC) typically develops postnatally in premature infants and shows pneumatosis intestinalis; atresia is recognized prenatally/at birth
Distinguishing Feature
Crohn's disease begins in childhood-adulthood with skip lesions and inflammatory changes; atresia is congenital, isolated obstruction
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralSmall bowel atresia is one of the neonatal emergencies requiring urgent surgery. In duodenal atresia, duodenoduodenostomy is the standard procedure. In jejunoileal atresia, resection + primary anastomosis is performed — partial resection of the proximal dilated segment reduces caliber mismatch. In apple peel atresia, remaining bowel length should be carefully evaluated — risk of short bowel syndrome is high. Associated anomalies (cardiac, Down syndrome, malrotation) should be investigated. Postoperative parenteral nutrition support is generally required.
Small bowel atresia is a neonatal condition requiring emergency surgery. It is treated with surgical anastomosis. In duodenal atresia, screening for Down syndrome and associated anomalies (30%) should be performed. Short bowel syndrome risk should be assessed in jejunoileal atresia.