“Atresia” is derived from the Greek work atretos , meaning not perforated. This term is used to describe a congenital absence or pathologic closure of a body opening or passage. When used to describe gastrointestinal anatomy, this word refers to luminal discontinuity resulting from an anatomic obstruction. “Stenosis” comes from the Greek work stenos , meaning narrow. This term refers to a partial obstruction of the lumen that allows for incomplete passage of material. Either of these conditions can affect any portion of the gastrointestinal tract. Herein, we focus on these conditions in the small bowel and colon.
Duodenum
Calder first described duodenal atresia as a cause for bowel obstruction in 1733. It was almost two centuries later, in 1916, that Ernst reported the first survivor. Fifteen years later, 250 cases had been reported with less than 10% survival. Recently, long-term survival rates have been reported to be as high as 90% with operative mortality (fewer than 30 days postoperative) as low as 3%. Both short- and long-term death typically results from associated anomalies, particularly congenital heart disease, rather than the issues related directly to intestinal reconstruction.
Embryology
In 1902, Tandler first proposed the commonly accepted, yet unsubstantiated, theory that the etiology of duodenal atresia is a failure of luminal recanalization. Initially, the duodenum develops as the distal portion of the foregut and the proximal portion of the midgut during the fourth week of gestation. These portions of the bowel grow rapidly and join immediately distal to the origin of the biliary system. During the next 2 weeks of gestation, the duodenal lumen is nearly completely obliterated due to the brisk expansion of the epithelial cell population. Over the next several gestational weeks, the duodenum recanalizes, with the second portion being the last to go through this process. Duodenal atresia or stenosis is thought to result from failure of this process rather than vascular compromise as is thought to occur with more distal abnormalities.
The development of the pancreas is linked with that of the duodenum. In the fourth week, pancreatic buds develop from the duodenal endoderm. A larger dorsal bud appears initially and then the smaller ventral bud develops at the future site of the ampulla of Vater. As the duodenum undergoes a normal clockwise rotation to form the typical adult “C-shape” configuration, the ventral pancreatic bud rotates dorsally. Normally, the two buds fuse in the eighth week. If the ventral bud fails to undergo complete rotation and remains anterior to the duodenum, the fusion process produces an annular pancreas, which is typically associated with complete or partial duodenal obstruction.
Incidence
Congenital duodenal obstruction occurs in approximately 1 in every 6000 births in the United States, whereas in Finland, the reported rate is appreciably higher (1 in 3400.) Approximately, two-thirds of these cases result from intrinsic bowel pathology. In the remaining patients, external compression from an annular pancreas, preduodenal portal vein, or Ladd’s bands is associated with the obstruction. Many children with duodenal atresia have associated abnormalities, which commonly include Down syndrome, malrotation, and congenital heart disease, which may significantly impact their disease course.
Clinical Presentation
Antenatal ultrasound will demonstrate polyhydramnios in 30% to 59% of children who have duodenal atresia. In addition, ultrasound performed in the third trimester may show a dilated, fluid-filled stomach and proximal duodenum.
Newborns with duodenal atresia will have emesis during the first hours of life. Obstruction is most frequently postampullary (~85%); thus, the vomitus is usually bilious. However, preampullary duodenal atresia is sufficiently common that nonbilious emesis must not be discounted entirely. The abdomen usually does not become distended because the obstruction is proximal enough within the gastrointestinal tract that vomiting can be an effective means of decompression. “Double-bubble” sign is the classic finding on abdominal plain film ( Figure 57-1 ). This is constituted by significant gaseous distension of the stomach and, to a lesser degree, the proximal duodenum with an otherwise gasless abdomen.
Duodenal webs or stenoses can be more difficult to diagnose. Some of these children will tolerate feeds, since they have only a partial obstruction. Abdominal X-rays will show air in the gastrointestinal tract distal to the duodenum. Upper gastrointestinal contrast studies may have a similar appearance to those found in malrotation or volvulus, and when in doubt immediate surgical exploration is warranted. Occasionally, children with partial obstruction are diagnosed much later in life during evaluation for reflux symptoms, emesis, or failure to thrive.
Classification ( Figure 57-2 )
Duodenal atresias (DAs) are categorized according to their anatomic features. Type I DA consists of obstruction due to a mucosal membrane. Occasionally, these membranes are fenestrated, in which case air and small amounts of enteric contents are able to pass distally. This type of DA includes the “windsock” variant in which the origin of the membrane is several centimeters proximal to the apex of the web. This appearance is thought to result from antegrade peristalsis and can be a pitfall for the inexperienced or occasional pediatric surgeon. It is important to note that the distal common bile duct and ampulla typically border or transverse the medial wall of the web. Type II DA is characterized by a fibrous cord connecting the two ends of the duodenum. Finally, type III DA is the most infrequent form and comprises two blind-ending bowel loops with no intervening mesentery. This form of atresia can be associated with biliary anomalies.
Treatment
Initial treatment of an infant with duodenal stenosis focuses on stabilizing the infant. A peripheral intravenous line is established, which allows for administration of fluids and antibiotics. The stomach is decompressed with an orogastric tube. Next, the child should be evaluated for any significant associated anomalies that would affect the care of the child during anesthesia. Specifically, an echocardiogram is obtained for any child with a murmur or clinical evidence of Down syndrome.
After correction of any initial metabolic or respiratory complications, the operation can be done on a prompt, planned basis. It commences through a transverse supraumbilical incision. The abdomen is thoroughly inspected, specifically evaluating for malrotation. If this is encountered, a Ladd’s procedure is performed. Next, the hepatic flexure of the colon is mobilized medially and the duodenum is completely exposed. Here the surgeon must note other variants including annular pancreas or preduodenal vein. These anomalies should be documented in the operative report but are otherwise left alone. Lateral attachments to the retroperitoneum are released, fully mobilizing the entire duodenum. A transverse incision is made just proximal to the apparent point of obstruction. Placement of this duodenotomy can be challenging in the setting of a partial obstruction. Subsequently, the ampulla should be clearly identified. Loupe magnification is very beneficial. This may be done by compressing the gallbladder and visualizing the location where bile enters the duodenum. Intestinal continuity is restored with a duodenoduodenostomy. This anastomosis is usually performed in a Kimura diamond-shape (proximal transverse to longitudinal distal) fashion or side-to-side fashion; however, the reconstruction should be tailored to the individual’s anatomy. Prior to completing the anastomosis, a small, red rubber catheter should be passed distally to be certain there are no additional intraluminal obstructions. Historically, these are present in 1% to 3% of children, yet more recent reports suggest that they are present in less than 1% of cases. Laparoscopic repair using the same principles is being performed selectively in some centers with good short-term (less than 30 day) outcomes. Further investigations with respect to long-term outcomes are needed before a minimally invasive approach can be widely adopted.
When treating or suspecting a windsock deformity, passing the orogastric tube through the pylorus is helpful in identifying the origin of the obstructing web. The tube is advanced until it meets resistance at the apex of the web. An indentation or puckering in the dilated proximal segment can be identified, and this site corresponds to the base of the membrane. The duodenotomy should be made just proximal to this site, and the web may be excised laterally as the ampulla is frequently located along the medial wall. The duodenotomy is then closed in layers. When the ampulla cannot be confidently identified in children with windsock or other deformities, a duodenoduodenostomy bypass is the most appropriate technique. If there is a significant size discrepancy between the dilated proximal and decompressed distal segments, the surgeon my elect to perform a tapering duodenoplasty on the lateral, antimesenteric border. There is real controversy among surgeons as to whether this modification improves outcomes.
Operative mortality for repair of duodenal atresia is approximately 4% and is most significant for children with complex associated heart anomalies. Postoperative care includes gastric decompression with an orogastric or nasogastric tube until the aspirate becomes clear and there is evidence of gastrointestinal function. During this period, infants are usually maintained on parenteral nutrition via peripherally inserted central catheter (PICC) or central venous catheter. Once the gastric tube is removed, feeds are gradually advanced until the infant tolerates full enteral feeds. This often requires several weeks.
Jejunoileum
Embryology
Spriggs hypothesized that in utero accidents, such as vascular occlusion, were the cause of small bowel atresias in the early 20th century. Ensuing clinical and experimental investigations demonstrate that vascular insult due to volvulus, internal herniation, or gastroschisis generated atresias. Animal models have confirmed that vascular disruption with resultant intestinal necrosis and reabsorption produces intestinal atresia.
Incidence
Small bowel atresia has been reported in approximately 1 in 5000 births. Jejunoileal atresia is associated with abdominal wall defects, meconium ileus, and cystic fibrosis. No sex predilection has been observed.
Clinical Presentation
Several important antenatal and postnatal signs warrant suspicion for jejunoileal atresia. Maternal polyhydramnios is observed in 24% of such patients. Prenatal ultrasound may demonstrate dilated, echogenic bowel. Infants may present with bilious emesis; this finding is seen earlier and more frequently in cases of proximal obstruction. Abdominal distension is more severe in distal lesions and usually takes hours or even days to manifest. Jaundice can be present in 20% to 30% of babies with small bowel atresia. This is attributed to delayed maturation of glucuronyl transferase as a result of unsuccessful enteral feedings.
The appearance of abdominal plain films is dependent on the level of the obstruction. Proximal small bowel atresias may produce few dilated loops or air fluid levels ( Figure 57-3 ), whereas distal lesions produce more dramatic radiographic and physical findings. Occasionally, a dominant dilated loop will be present. Evaluation with contrast enema typically demonstrates a microcolon in the setting of small bowel atresia; however, this finding is nonspecific. This study is important to distinguish small bowel atresias from other possible conditions such as Hirschsprung’s disease or small left colon syndrome.
