Small bowel atresia (ORPHA:1201)
A rare, congenital defect of the small intestine characterized by disruption in the normal small intestine continuity, resulting in intestinal obstruction. The malformation may be classified in four different types of small bowel atresia (SBA) based on the anatomical obstruction.
Epidemiology
The prevalence at birth ranges from 1/7,000-25,000 in Europe with equal male/female distribution. About one third of patients are premature. Other congenital anomalies are present in < 10% and occur more frequently with type IIIb or type IV atresia.
Clinical description
The type of SBA is important for surgical treatment and prognosis. Type I corresponds to a narrowed intestine with intact walls and mesentery, and a mucous membrane obstructing the lumen. Type II is a true short segment atresia with a fibrous cord between the upper and lower pouch, without a mesenteric defect. Type IIIa consists of a ''V''-shaped mesenteric defect and a blind-ending, dilated proximal pouch without fibrous connection to the distal part. Type IIIb (''apple-peel'', ''Christmas tree'' atresia) is characterized by proximal jejunal atresia, absence of the superior mesenteric artery and a large mesenteric defect with the small bowel assuming a helical configuration around a single perfusing vessel with possible distal type I or II atresia. Type IV is the combination of multiple atresias. Clinical presentation of all types occurs in the first 24-48h of life, depending on the proximity of the first atretic tract to the Treitz ligament, with signs of bowel obstruction (feeding intolerance, bilious vomiting, abdominal distention). Meconium can be passed normally. Complicated cases might present abruptly, with signs of perforation, intussusception, volvulus or internal hernia. Perforation of the proximal dilated bowel can occur in both the antenatal and postnatal life causing meconium peritonitis. In the case of low atresia or incomplete obstruction, clinical manifestations and diagnosis are usually delayed, with failure to thrive and progressive intestinal obstruction.
Etiology
The prevailing hypothesis is that an ischemic insult affecting single or multiple segments of the developed fetal intestine with subsequent necrosis and resorption is the main cause of SBA. Disruption of an embryologic pathway has been suggested for familial forms but no causative genes have yet been identified.
Diagnostic methods
Diagnosis relies on clinical evaluation, pre- and post-natal history, together with abdominal X-rays that reveal a distended proximal bowel with no air distally. Abdominal ultrasonography shows dilated small intestinal loops with fluid collection. In case of intestinal perforation free air is present. In children with distal defects and/or poor sucking, radiological and clinical findings can be delayed. A contrast enema can be useful.
Differential diagnosis
Differential diagnosis includes: colonic atresia, midgut volvulus, meconium ileus, duplication cysts, internal hernias, paralytic ileus, high Hirschsprung´s disease and hypothyroidism.
Antenatal diagnosis
About 30-50% of cases are suspected antenatally. Dilated bowel loops and polyhydramnios are the typical findings.
Genetic counseling
Whilst the majority of cases are sporadic, familial cases have been reported and thus genetic counselling is always recommended. An autosomal recessive pattern of inheritance of multiple atresias has been documented.
Management and treatment
Bowel decompression via naso-gastric tube, fluid resuscitation and antibiotics are the bridge to surgical correction (restoration of bowel continuity). Surgery must not be delayed, in order to avoid complications. Preserving the largest amount of small bowel tissue is mandatory during surgery. Resections and tapering must be considered. Prolonged parenteral nutrition is often required, particularly in the case of short bowel syndrome. In children on permanent parenteral nutrition, intestinal lengthening procedures may be considered to decrease the need for parenteral nutrition.
Prognosis
The current survival rate is over 90%. Prognosis mainly depends on the length of the remaining bowel and the subsequent possibility of a short bowel syndrome. Type IIIb and type IV carry a worse prognosis.

                            Last update: 
                            July 2021


                            - Expert reviewer(s): 
                            Dr Francesco FASCETTI LEON | ERNICA* - Pr Niels QVIST | ERNICA* - Dr Alessandra RANCAN 


                                * European Reference Network