Atresia

Clinical

Atresia can occur anywhere within the small bowel, presenting in the neonatal period as obstruction.

The duodenum is the most common site of atresia. The duodenum undergoes a solid phase during the embryological development of the hepatobiliary system and pancreas.  It recanalizes during the eighth to tenth weeks by accumulation of vacuoles.  Insults during this stage of development can lead to various forms of luminal narrowing, ranging from web formation to complete luminal obliteration. Duodenal atresia is strongly associated with Dpwn’s syndrome, with 40% possessing trisomy 21. Fifty percent of patients with duodenal atresia also have associated anomalies (cardiac, genitourinary, anorectal).  There is an association with VATER (vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, and renal and radial anomalies) syndrome. Prenatally, growth retardation and polyhydramnios may be present. In the neonatal period, atresia presents with bilious or clear emesis hours after birth. Stenosis (less severe than atresia) may be more indolent, presenting as failure to thrive and dehydration.

Jejunal and ileal atresia occur less commonly than duodenal atresia and are not associated with Down’s syndrome.  The majority occur as isolated abnormalities, with only 10% having other associated anomalies. The etiology of jejunal/ileal atresia is believed to be an in utero vascular accident that causes necrosis and resorption of intestine. The severity (classification) ranges from stenosis to complete luminal obliteration. Proximal lesions present predominantly with bilious emesis; whereas, more distal lesions present with a greater degree of abdominal distention.   

Treatment consists of a two-fold approach. Supportive measures are instigated initially, including gastric decompression, fluid resuscitation, and thermoregulation. However, prompt surgical correction is mandatory for definitive treatment.

Radiology

Plain films are usually the first imaging studies performed. The characteristic plain film finding of duodenal atresia is the “double bubble” sign, in which there is a dilated stomach and duodenum proximal to obstruction, separated by an intact pylorus. Jejunal and ileal atresias evince a predominantly gasless abdomen with variable air-fluid levels, depending of the location of atresia.

Fluoroscopy is used to confirm narrowing or obliteration of the lumen. Upper GI study with small bowel follow-through is most often the test performed. It confirms the presence of atresia and helps to exclude other causes of emesis, such as malrotation with midgut volvulus.

Barium enema often demonstrates a microcolon, indicative of congenital obstruction. It helps rule out other causes of obstruction, such as Hirschsprung disease or meconium ileus.

Double bubble - Chest and abdominal film of a patient with duodenal atresia. 
Note the characteristic "double-bubble" sign indicated by the arrows.