Congenital duodenal obstruction occurs due to either an intrinsic or extrinsic lesion. The most common cause of duodenal obstruction is atresia. The etiology of duodenal atresia remains unclear. The most widely accepted hypothesis was proposed by the Viennese anatomist Julius Tandler in 1900. Tandler formulated his hypothesis from his analysis of duodenal development in normal embryos. He observed that as the duodenum progresses through early development, the epithelial lining undergoes a rapid proliferative phase that occludes the lumen of the intestinal tube on day 42 (Carnegie stage [CS] 17) of development. Over the course of the ensuing 2 days the plug of epithelial tissue develops cracks that give way (CS 18), reestablishing the continuity of the intestinal lumen ( Fig. 28.1 ).

Histology of human duodenal development from Carnegie stage 13 to Carnegie stage 18. The duodenal epithelial layer ( green arrow ) proliferates, gradually occluding the lumen with an epithelial plug by CS17 which then recanalizes by CS18.

Tandler stated at the end of his paper on the subject:

“If one keeps in mind the fact that on one hand the epithelial occlusion of the duodenum represents a normal event, but on the other hand that it is exactly in this place that most pathologic occlusions of the intestine occur, the question does not appear unjustified to ask whether these processes relate to each other, that is, whether they are causally related. It would not be impossible that in rare cases the physiologic atresia remains and develops into a congenital atresia. It is clear to me that the opinion here represented does not exceed the status of a new hypothesis, and it is not meant to exceed this.”

Over the years, through publication and republication, Tandler’s hypothesis has come to exceed its own status and is frequently presented as fact in the absence of new supportive evidence since he first put forth his hypothesis. Given the lack of clarity on the origins of this defect, it is worthwhile reviewing what in fact is known about how these defects come to be.

The role of genetics was first proposed in the 1970s with the observation of familial cases of duodenal atresia. There are currently two reliable genetic models of duodenal atresia. The homozygous mutation of either the Fibroblast growth receptor 2IIIb or its cognate ligand Fgf10 ^, results in duodenal atresia in mouse embryos about 40% of the time. One hundred percent of these embryos also develop type III atresias of the distal colon. Atresias of the duodenum are type III approximately 94% of the time, whereas the remaining 6% are type I defects in which there is a luminal interruption in the continuity of the duodenum. ^{, ,}

The earliest events in this animal model appear to be an increase in the rate of epithelial apoptosis compared to controls at embryonic day (E) 10.5 followed by the absence or attrition of epithelial cells in the proximal loop of the duodenum a full day and a half later at E12. Whether the increase in apoptosis is a critical event that results in the absence of the epithelium or whether there are other events in play such as cell movement remains unclear.

By E12.5 the affected segment of duodenum has narrowed dramatically and by E13.5 ( Fig. 28.2 ) it has completely disappeared, resulting in the typical type III defect. In contrast to normal human development where an epithelial plug forms in the duodenal region from exuberant epithelial growth, the duodenum of the wild-type and mutant mouse embryos never form occlusive epithelial plugs in this anatomical region. Interestingly, the pyloric channel of the wild-type embryos forms a nearly occlusive plug at a much later developmental time point: E14.0 ( Fig. 28.3 ), yet pyloric atresia has not been observed in wild-type mice.

Three-dimensional reconstructions of H&E sections of duodenal atresia formation in Fgfr2IIIb−/− embryos. Embryonic day (E): (A) E10.5 (CS14); (B) E11.5 (CS 16); (C) E12.5 (CS18); (D) E13.5 (CS20). Endoderm ( red ) is visibly absent in the duodenal region ( white arrow ) by E11.5. The surrounding mesoderm (aquamarine) begins to involute with a visible narrowing evident at E12.5 (CS16). White measure bars indicate 50 μm.

A nearly occlusive epithelial plug in the pyloric channel of a mouse embryo at day 14.0 (CS21).

The severity of the defect in this model can be shifted by reducing the amount of retinoic acid via a mutation in a single copy of the Retinaldehyde dehydrogenase 2 gene. The addition of this mutation results in the majority of the duodenal atresias manifesting as type I or type II and, only rarely, type III defects. What we can state from these models is that atresias are associated with focal loss of epithelial cells as opposed to a hyperproliferative epithelial state that fails to resolve as proposed by Tandler, and, that type I to type III defects represent a continuum of severity arising from a single genetic or molecular mechanism.

There have been isolated reports of specific mutations associated with duodenal atresia in humans. It has been reported in one patient with 17q12 microdeletion, which includes the gene for hepatic nuclear factor β-1. Additionally, mutation in transcription factors critical for foregut development has been implicated. Homozygous mutation of RFX6 , which is critical for normal pancreatic development, has been reported to be associated with duodenal atresia. Mutation in the FoxF1 gene, which is involved in the sonic hedgehog signaling pathway, has also been reported to be associated with duodenal atresia. Interestingly, mouse models in which both copies of this gene are mutated do not manifest intestinal atresias.

With the decreasing cost of complete genomic sequencing, it is likely that mutations in many genes will be found to be associated with duodenal atresia. From there, molecular and cellular mechanisms underpinning this defect will be better delineated. These discoveries may also shed light on one of the more vexing problems in children with atresias: poor intestinal motility. Insights into motility in this clinical setting may be widely applicable to several unrelated and poorly understood intestinal motility disorders that plague children and adults. Equally important, identification of associated genes will result in screening tools that can diagnose embryos at risk for these defects very early in pregnancy. This will provide an opportunity for early intervention through gene editing. For now, the focus of treating this defect will remain on the surgical interventions required and how we can improve the quality of postoperative management.

Annular pancreas as an etiology for duodenal obstruction warrants special mention as this form of obstruction is likely due to failure of duodenal development rather than a true constricting lesion. Thus, the presence of an annular pancreas is simply a visible indication of an underlying atresia or stenosis. Between the fourth and eighth weeks of gestation, the pancreatic buds merge. In annular pancreas, the tip of the ventral pancreas becomes fixed to the duodenal wall forming a nondistensible, ring-like or annular portion of pancreatic tissue surrounding the descending part of the duodenum. In annular pancreas associated with duodenal obstruction, the distal biliary tree is often abnormal and may open proximal or distal to the atresia or stenosis. ^, Other reported biliary abnormalities associated with duodenal obstruction include biliary atresia, gallbladder agenesis, stenosis of the common bile duct, choledochal cyst, and immune deficiency.

Anatomically, duodenal obstructions are classified as either atresias or stenoses. An incomplete obstruction, due to a fenestrated web or diaphragm, is considered a stenosis. Most stenoses involve the third and/or fourth part of the duodenum. Atresias, or complete obstruction, are further classified into three morphologic types ( Fig. 28.4 ). Type I atresias account for more than 90% of all duodenal obstructions and contain a luminal diaphragm that includes mucosal and submucosal layers. A diaphragm that has ballooned distally (windsock) is a type I atresia. ^, It is important to understand that the anatomy of the windsock may lead to a portion of the dilated duodenum being distal to the actual obstruction ( Fig. 28.5 ). Type II atresias are characterized by a dilated proximal and collapsed distal segment connected by a fibrous cord. Type III atresias have an obvious gap separating the proximal and distal duodenal segments.

Duodenal atresia (and stenosis) is depicted. In type I (A), either a membrane (B) or web (C) causes the intrinsic duodenal obstruction. There is no fibrous cord and the duodenum remains in continuity. Type II is characterized by complete obliteration of a segment of the duodenum with the proximal and distal portions attached via a fibrous cord. Type III is associated with complete separation of the dilated proximal duodenum from the collapsed distal duodenum.

Illustration of the “windsock” deformity, a variant of type I duodenal atresia. Note the actual position of the origin of the web in relation to the extent of proximal duodenal dilation and the distal collapsed duodenum.

More than 50% of affected patients with duodenal atresia have associated congenital anomalies. Approximately 30% are associated with trisomy 21, 30% with isolated cardiac defects, and 25% with other gastrointestinal (GI) anomalies. ^, Approximately 45% of patients are premature, and about one-third exhibit growth retardation. ^, Neonates with duodenal atresia and trisomy 21 have an associated cardiac anomaly in approximately 50% of cases.

The obstruction can be classified as either preampullary or postampullary, with approximately 85% of obstructions located distal to the ampulla. With complete or almost complete obstruction, the stomach and proximal duodenum become significantly dilated. The pylorus is usually distended and hypertrophic. The bowel distal to the obstruction is collapsed, except in the case of a windsock deformity in which the distal bowel is dilated to a variable length depending on the length of the windsock (see Fig. 28.5 ). In most cases of duodenal obstruction, the GI tract can be decompressed proximally. The presence of polyhydramnios during gestation is variable in the setting of complete duodenal obstruction, occurring in between 32% and 81% of pregnancies. ^, Intrauterine growth retardation is also common, presumably from nutritional deprivation from the swallowed amniotic fluid.

With advancements of fetal ultrasonography, a majority of infants with duodenal atresia are diagnosed prenatally. ^{, ,} In complete duodenal obstruction, fetal sonographic evaluation may detect two intraabdominal fluid-filled structures consistent with a double bubble in 44%–81% of cases. ^{, ,} The timing of prenatal detection of duodenal atresia is reported to occur late in pregnancy, usually between the 7th and 8th months of gestation ^{, ,} despite duodenal obstruction occurring by week 12 of gestation. The reason for failure of early prenatal detection is not entirely clear. It is currently believed that immature gastric emptying in utero may contribute to low gastric pressures, resulting in failure to dilate the proximal duodenum until later in gestation. While both circular and longitudinal muscle layers are present in the stomach by week 8 of gestation, pressure amplitudes at 25 weeks are only 60% of term gastric pressures. ^, Other parameters on fetal ultrasound that have been proposed to be an indirect indication of duodenal obstruction, such as a large abdominal circumference and polyhydramnios, have been shown to have little diagnostic value. If suspicion for duodenal atresia persists following ultrasonography, fetal magnetic resonance imaging may be a useful diagnostic modality.

The diagnosis of duodenal atresia during pregnancy is associated with improved neonatal morbidity, decreased time to full enteric feeds, and lower hospital lengths of stay compared to those diagnosed postnatally. ^{, ,} In addition, a prenatal diagnosis can result in parental counseling and delivery planning due to associated anomalies and the need for postnatal surgical intervention. Following the diagnosis, obtaining a dedicated fetal ultrasound is critical due to the possibility of a concomitant congenital heart anomaly, as previously discussed.

In neonates who are not diagnosed during the prenatal period, the presentation of duodenal obstruction varies depending on whether the obstruction is complete or incomplete, and the location of the ampulla of Vater in relation to the obstruction. The classic presentation is that of bilious emesis within the first hours of life in an otherwise stable neonate. In about 10% of cases, however, the atresia is preampullary and the emesis is nonbilious. In neonates with duodenal atresia, the abdomen may be distended or scaphoid. Aspiration via an orogastric (OG) tube of more than 20 mL of gastric contents in a newborn suggests intestinal obstruction, as normal aspirate is less than 5 mL. For patients with stenosis, the diagnosis is often delayed until the neonate has started on enteral feeds and feeding intolerance develops, with emesis and gastric distention.

In antenatally suspected cases of duodenal obstruction, as well as in neonates with a clinical presentation consistent with a proximal bowel obstruction, an upright abdominal radiograph is usually sufficient to confirm the diagnosis of duodenal atresia. The diagnostic radiographic presentation of duodenal atresia is that of a double-bubble sign with no distal bowel gas ( Fig. 28.6 ). The proximal left-sided bubble represents the air- and fluid-filled stomach, while the dilated proximal duodenum represents the second bubble to the right of midline. In almost all cases of duodenal atresia, the distal bowel is gasless. However, the presence of distal gas does not absolutely exclude the diagnosis of atresia as there are very rare reports of bifid common bile ducts, with insertion of one of the ducts proximal and the other distal to the atretic segment which allows the air to bypass the atresia. In neonates whose stomach has been decompressed by either NG aspiration or vomiting, 40–60 mL of instilled air into the stomach will reproduce the double bubble. Rarely, the biliary tree is air filled, and a variety of pancreatic and biliary anomalies have been demonstrated ( Fig. 28.7 ). At our institution, neonates who present with bilious emesis and a decompressed stomach on plain abdominal films receive an abdominal ultrasound to exclude malrotation and volvulus. With duodenal stenosis, a double-bubble sign is often not present, and the diagnosis is usually made with a contrast study ( Fig. 28.8 ).

Classic “double-bubble” sign. This abdominal radiograph in a newborn shows a markedly distended stomach and duodenal bulb without evidence of distal intestinal air.

This schematic depicts several of the variations in biliary ductal anatomy seen in babies with duodenal atresia.

An upper gastrointestinal contrast study is shown illustrating a duodenal web. Contrast medium outlines the markedly dilated proximal duodenum ( D ) with a collapsed distal segment. Note the absence of contrast agent at the location of the tiny web ( arrow ). P , pylorus.

After the diagnosis of duodenal atresia is made, appropriate resuscitation is required with correction of fluid balance and electrolyte abnormalities, in addition to gastric decompression. In babies with duodenal obstruction, we obtain a complete metabolic profile, complete blood count, coagulation studies, type and screen, abdominal and spinal ultrasound, and two-dimensional echocardiography prior to any operation. An emergency operation is only performed in cases where malrotation with concurrent volvulus cannot be excluded.

Prior to the mid-1970s, duodenojejunostomy was the preferred technique for correcting duodenal atresia or stenosis. ^{, ,} Since then, the various techniques utilized include side-to-side duodenoduodenostomy, diamond-shaped duodenoduodenostomy, partial web resection with Heineke–Mickulicz-type duodenoplasty, and tapering duodenoplasty. The long side-to-side duodenoduodenostomy, although effective, is associated with a high incidence of anastomotic dysfunction and prolonged obstruction. Blind-loop syndrome appears to be more common in patients treated with duodenojejunostomy. Gastrojejunostomy should not be performed as it is associated with a high incidence of marginal ulceration and bleeding.

Currently, the preferred technique is either laparoscopic or open duodenoduodenostomy ^, The duodenoduodenostomy anastomosis was traditionally made via a side-to-side configuration; however, a proximal transverse to distal longitudinal (diamond-shaped) anastomosis in a single layer is now preferred. ^{, , ,} For the open approach, either a right upper quadrant supraumbilical transverse incision or an umbilical crease incision is utilized. After mobilizing the ascending and transverse colon to the left, the duodenal obstruction is readily exposed. Malrotation should be evaluated at this point as it can occur in association with congenital duodenal obstruction in up to 30% of patients. A sufficient length of duodenum distal to the atresia is mobilized to allow for a tension-free anastomosis. A transverse duodenotomy is made in the anterior wall of the distal portion of the dilated proximal duodenum and a similar-length duodenotomy is made in a vertical orientation on the antimesenteric border of the distal duodenum. The anastomosis is then fashioned by approximating the end of each incision to the appropriate mid-portion of the other incision ( Fig. 28.9 ). Tapering duodenoplasty is generally not necessary as the proximal duodenal dilation usually resolves after relief of the obstruction. Muscular continuity of the duodenal wall suggests a windsock deformity or diaphragm. This finding should precipitate extra vigilance in the operative correction because the dilated and collapsed bowel are both distal to the windsock, and have been anastomosed in error. ^,

The technique of duodenoduodenostomy. A diamond-shaped anastomosis is created via the proximal transversely oriented and distal vertically oriented duodenotomies.

The laparoscopic repair of duodenal atresia has been reported as one of the most challenging operations in pediatric surgery. This approach was first described by Bax in 2001 and Rothenberg in 2002. ^, The standard laparoscopic approach is carried out by placing the patient in the supine position and accessing and insufflating the abdomen through the umbilicus with a 5-mm port. Two addition working ports are placed, one in the baby’s right lower quadrant and one in the right mid-epigastric region to allow for the use of instruments. A liver retractor can be placed in the right or left upper quadrant if necessary. Alternatively, the liver can be elevated by placing a transabdominal wall suture around the falciform ligament and tying it outside the abdomen ( Fig. 28.10 ). The duodenum is mobilized, and the location of obstruction is identified. Using the same principles that have been described for the open approach, a standard diamond-shaped anastomosis is created via intracorporeal suturing ( Fig. 28.11 ). Other techniques have been reported for creating the anastomosis, including the use of U-clips and a miniature stapler. ^{, ,} Despite promising outcomes and decreased operative times with the use of U-clips compared to the standard intracorporeal suturing, U-clips are no longer marketed or available.

Two approaches to placement of the instruments for a laparoscopic duodenal atresia repair. (A) The two right-sided instruments are the primary working sites for the surgeon. The liver retractor ( arrow ) has been placed in the left midepigastric region. The falciform ligament has been elevated by a suture placed under it and tied over the red rubber catheter, which is used as a bolster. The suture ( dotted arrow ) exteriorized in the infant’s left upper abdomen was placed in the dilated proximal duodenum so that it could be easily manipulated. (B) This is a similar configuration except the instrument elevating the liver ( arrow ) is placed in the infant’s right upper abdomen rather than the left upper abdomen. The suture that was placed through the proximal dilated duodenum in (A) was not needed in this particular case.

(A) This view shows a completed laparoscopic repair of duodenal atresias. (B) A postoperative contrast study shows a widely patent duodenoduodenostomy with no leak.

Early studies of the laparoscopic repair suggested unacceptably high rates of anastomotic leak; however, recent studies which compare the open and laparoscopic repair of duodenal atresia show no difference in anastomotic complications. ^, In addition, the use of the laparoscopic technique is associated with a shortened hospital length of stay and decreased time to resuming enteral feeding and a shorter time to goal feeds. ^{, , ,}

The historical approach to enteral feeding following duodenal atresia repair involved a period of waiting for the gastric output to become less bilious and the volume of gastric drainage to decrease, indicating return of intestinal function. One study showed that the time spent waiting for the gastric output to decrease is likely not necessary, as all the patients undergoing laparoscopic duodenoplasty were fed without adverse events after an upper GI contrast study on day 5 revealed no leak. Additionally, a recent study of neonates with duodenal atresia status post repair compared gastric residual volumes following feeding in patients with either a liberal or conservative feeding plan. The study revealed no difference in post feeding gastric residuals despite a higher volume and rate of feeds in the neonates with a liberal feeding plan. Furthermore, expedited return to enteral feeding may reduce the risk of neonates with duodenal atresia developing cholestasis due to prolonged parenteral nutrition.

Historically, during repair of duodenal atresia, it was been emphasized that inspecting the entire small bowel to identify a second atresia was important. Given that duodenal atresia and jejunoileal atresia do not share common embryologic etiologies, a recent metaanalysis was performed on research articles that pertained to duodenal atresia and/or intestinal atresia to quantify the incidence of concomitant jejunoileal atresia. The metaanalysis included over 2000 neonates with duodenal atresia and found the pooled rate of concomitant jejunoileal atresia to be 2.8% (range 0.5%–7.1%). In addition, the rate of missed atretic segments was higher among patients who underwent laparoscopic repair compared to an open repair (3% vs. 0.3%). The need for inspection of the entire bowel is controversial, with many surgeons opting to omit this as part of standard of care due to the low incidence of a concomitant distal atresia.

Early postoperative mortality for duodenal atresia repair has been reported to be as low as 3%–5%, with the majority of deaths occurring secondary to complications related to associated congenital abnormalities. ^, Long-term survival approaches 90%. ^, Long-term complications have been noted following repair and include delayed gastric emptying, severe gastroesophageal reflux, bleeding peptic ulcer, megaduodenum, duodenogastric reflux, gastritis, blind-loop syndrome, and intestinal obstruction related to adhesions. Children and adolescents with a history of duodenal atresia have similar quality-of-life measures as their peers who did not have duodenal atresia.

Neonates with duodenal atresia and trisomy 21 have a higher rate of associated anomalies including congenital cardiac and GI anomalies such as esophageal atresia. Following the establishment of bowel continuity, patients with trisomy 21 are more likely to have esophageal and gastric complications. In addition, those with trisomy 21 have increased difficulty with oral motor delay, swallowing dysfunction, and airway difficulties, and may benefit from placement of a gastrostomy tube.

Jejunoileal atresia is the most prevalent form of intestinal atresia, occurring in 1–3 of every 10,000 live births. It occurs equally in males and females, and about one in three infants is premature. Although the majority of cases are thought to occur sporadically, familial cases of intestinal atresias have been described. Associated concomitant congenital abnormalities are less common among neonates with jejunoileal atresia compared to those with duodenal atresia. It is generally accepted that jejunoileal atresia results from an intrauterine ischemic accident to the midgut, affecting a single or multiple segment(s) of developed intestine. ^, Intrauterine vascular disruption can lead to ischemic necrosis of the bowel with subsequent resorption of the affected segment or segments ( Fig. 28.12 ).

The proposed mechanism of vascular compromise and subsequent development of jejunoileal atresias is depicted.

The hypothesis that most cases of jejunoileal atresia occur secondary to a vascular disruption during fetal life was first described by Barnard and Louw in 1956. This hypothesis has been demonstrated in animal studies and through clinical evidence. By creating isolated mesenteric vascular insults and interference with the segmental blood supply to the small intestine in fetal dogs, researchers observed different degrees and patterns of intraluminal obstruction, reproducing the spectrum of stenosis and atresia found in humans. Moreover, the presence of bile, lanugo hair, and squamous epithelial cells from swallowed amniotic fluid distal to an atresia suggests that the atresia occurs subsequent to some event, but that at some time in gestation the intestinal lumen was patent, thus allowing passage of these contents. Additionally, atresias seen in association with other intrauterine vascular insults such as fetal intussusception, midgut volvulus, thromboembolic occlusions, internal hernias, and incarceration or snaring of bowel in an omphalocele or gastroschisis have contributed to wide acceptance of this hypothesis. ^, Critics of the vascular hypothesis note that nearly half of all jejunoileal atresia cases occur without evidence of an inciting incident to result in a vascular insult. Further, some argue that the robust collateral network of vasculature in the small bowel mesentery would not allow for a vascular insult to occur. ^,

No correlations have been found between jejunoileal atresia and paternal or maternal disease. However, the use of maternal vasoconstrictive medications, i.e., cocaine, pseudoephedrine, and amphetamine, as well as maternal cigarette smoking in the first trimester of pregnancy, has been shown to increase the risk of small-bowel atresia, further supporting the vascular hypothesis. ^, Chromosomal abnormalities are seen in less than 1% of the patients with jejunoileal atresia.

The presence of associated extraabdominal organ abnormalities in jejunoileal atresia is low (<10%) due to its occurrence later in fetal life and the localized nature of the vascular insult. Rarely, jejunoileal atresia has been found in patients with Hirschsprung disease, cystic fibrosis, malrotation, Down syndrome, anorectal and vertebral anomalies, neural tube defects, congenital heart disease, and other GI atresias. ^{, ,} Methylene blue, previously used for amniocentesis in twin pregnancies, has been implicated in causing small-bowel atresia.

Although jejunoileal atresias are usually not hereditary, there is a well-documented autosomal recessive pattern of inheritance of multiple atresias. In these cases, intestinal rotation was normal, mesenteric defects were never observed, and lanugo hairs and squamous cells were not identified distal to the most proximal atresia. All these findings suggest an early intrauterine event. Survival is poor in these infants, even with successful bowel resection.

The Grosfeld classification system separates these jejunoileal atresia into four groups ( Fig. 28.13 ). This classification has significant prognostic and therapeutic value as it emphasizes the importance of associated loss of intestinal length, abnormal collateral intestinal blood supply, and concomitant atresia or stenosis. In the setting of multiple intestinal atresias, the most proximal atresia determines whether the atresia is classified as jejunal or ileal atresia. Multiple jejunoileal atresias can be found in up to 30% of patients. ^,

The classification system for jejunoileal atresia and stenosis is seen.

Type I Atresia

In type I jejunoileal atresia, the intestinal obstruction occurs secondary to a membrane or web formed by both mucosa and submucosa, while the muscularis and serosa remain intact (see Figs. 28.13B and 28.14 ). On gross inspection, the bowel and its mesentery appear to be in continuity. However, the proximal bowel is dilated while the distal bowel is collapsed. With the increased intraluminal pressure in the proximal bowel, bulging of the web into the distal intestine can create a windsock effect. As with stenosis, there is no foreshortening of the bowel in type I atresias.

(A) In this infant with abdominal distention and evidence of a congenital bowel obstruction, a type I jejunal atresia was found. Note the mesentery is intact and the small, distal jejunum is connected to the very dilated, proximal jejunum. (B) The ∗ denotes the proximal enterotomy and distal web causing the intestinal obstruction.

Type III(a) Atresia

In type III(a) atresia, the proximal bowel ends blindly with no fibrous connecting cord to the distal intestine. A V-shaped mesenteric defect of varying size is present between the two ends of intestine (see Figs. 28.13D and 28.15 ). The dilated, blind-ending proximal bowel is often aperistaltic and frequently undergoes torsion or becomes overdistended, with subsequent necrosis and perforation occurring as a secondary event. In this scenario, the total length of the small bowel is variable (but usually less than normal), owing to intrauterine resorption of the affected bowel.

This baby was suspected of having a proximal jejunal atresia based on symptoms of bilious emesis and the abdominal film. (A and B) At operation, this type III(a) jejunal atresia was found. Note the V-shaped mesenteric defect between the dilated proximal atretic bowel and the distal decompressed bowel. Due to the size discrepancy between the two ends of the intestine, the proximal dilated bowel was resected at the arrow and an end-to-side anastomosis was performed. (C) The operation was performed through a slightly extended umbilical incision. The baby recovered nicely, and no complications developed.

Type III(b) Atresia

Type III(b) atresia (apple-peel, Christmas tree, or Maypole deformity) consists of a proximal jejunal atresia, absence of the superior mesenteric artery beyond the origin of the middle colic branch, agenesis of the dorsal mesentery, a significant loss of intestinal length, and a large mesenteric defect (see Fig. 28.13E). The decompressed distal small bowel lies free in the abdomen and assumes a helical configuration around a single perfusing vessel arising from the ileocolic or right colic arcades ( Fig. 28.16 ). Occasionally, additional type I or type II atresias are found distal to the initial atresia. It has also been shown that type III(b) atresias are significantly more likely to present with volvulus as well as risk for impaired vascularity of the distal bowel. This type of atresia has been found in families with a pattern suggestive of an autosomal recessive mode of inheritance. It also has been encountered in siblings with identical lesions and in twins.

(A) The operative findings in a neonate with a type III(b) intestinal atresia are seen. Note the classic “apple-core” or “Christmas tree” deformity as well as the wide mesenteric gap between the proximal dilated bowel and distal decompressed ileum. Also, the colon and distal small bowel are perfused through a single artery ( arrow ) running through the mesentery of the distal bowel. (B) This operation was performed through a small umbilical incision. This baby recovered nicely and has not developed any complications.

The occurrence of intestinal atresia in other siblings, the association of multiple atresias (15%), and the discordance in a set of apparently monozygotic twins may point to more complex genetic transmission with an overall recurrence rate of 18%. ^{, ,} Infants with this anomaly are often premature, and up to 50% may have malrotation. Short bowel syndrome is present in nearly 75% of cases. Accordingly, there is increased morbidity (63%) and mortality (54%) in this population. ^, Type III(b) atresias are most likely the result of a proximal superior mesenteric arterial occlusion with extensive infarction of the proximal segment of the midgut. Also, it can develop from a midgut volvulus. ^, Primary failure of development of the distal superior mesenteric artery has also been suggested as an etiologic factor. However, this is unlikely because meconium is usually found in the bowel distal to the atresia. This finding indicates that the atresia develops after bile secretion begins, which occurs around week 12 of intrauterine life. The superior mesenteric artery develops much earlier than 12 weeks.

The ischemic changes from the intrauterine vascular accident seen in jejunoileal atresia result in morphologic, structural, and functional abnormalities in the remaining proximal and distal small bowel. ^{, ,} The blind-ended proximal bowel becomes dilated and hypertrophied with histologically normal villi but lacks effective peristaltic activity. In addition, the proximal bowel is deficient in mucosal enzymes and muscular adenosine triphosphatase production. At the level of the atresia, the ganglia of the enteric nervous system are atrophic with minimal acetylcholinesterase activity. These changes are most likely secondary to local ischemia. Obstruction alone can elicit similar, but less severe, morphologic and functional abnormalities. Experimental studies showing that the intestinal atresia results from ischemic necrosis of the intestine also demonstrate a precarious blood supply to the proximally dilated bowel. This unstable blood supply has been confirmed with postmortem injection of barium sulfate into the mesenteric vessels. ^{, ,} The etiology of poor perfusion to the proximal bowel segment has also been postulated to be due to distention from swallowing air and not from the vascular accident. Swallowing air can lead to distention and increased intraluminal pressure or torsion of the blind-ended proximal bowel. The good results of the tapering procedure without resection of the bulbous portion of dilated proximal bowel would support that the vascular and nerve supply to the proximal and distal bowel adjacent to the atretic region are normal. However, in some neonates the tapering procedure is complicated by mucosal and neural dysfunction. Defective peristalsis is commonly noticed near the atretic area, thus supporting resection of the dilated bulbous proximal end for better function. Because the proximal end of the distal atretic bowel has been subjected to a similar insult, a small portion of it should be resected at the time of operative correction as well.

Although prenatal ultrasound is more reliable at detecting duodenal atresia, in recent years it has become useful in diagnosing jejunoileal atresia as well. Recent studies suggest that prenatal or fetal ultrasonography is able to detect jejunoileal atresia in 29%–50% of cases. ^{, ,} Prenatal ultrasound findings may demonstrate dilated loops of bowel, polyhydramnios, ascites, and enhanced bowel wall which may not be present early in gestation or with very distal obstructions. ^, A fetus with these abnormal findings should elicit further work up for familial GI abnormalities as well as referral for prenatal evaluation. Most patients with jejunoileal atresia will not be diagnosed prenatally. The presentation of jejunoileal atresia in neonates is similarly to other conditions that cause intestinal obstructions such as intestinal malrotation with midgut volvulus, internal herniation, Hirschsprung disease, and meconium ileus. Due to the possibility of ischemic compromise to the small bowel (midgut volvulus, internal herniation) prompt work up must be performed in neonates with signs and symptoms of intestinal obstruction.

Neonates with jejunoileal atresia or stenosis present with symptoms consistent with bowel obstruction, including bilious emesis and abdominal distention. Although meconium may appear normal, it often contains gray plugs of mucus. Occasionally, blood per rectum may be observed if there is type III(b) atresia with distal bowel ischemia.

Compared to jejunoileal atresia, jejunoileal stenosis is more likely to cause diagnostic difficulty. This difficulty is in part due to the nonspecific presentation of intermittent partial small-bowel obstruction and/or malabsorption, which often are self-limited and may improve without treatment. Despite the presence of stenosis, clinical investigations may initially be normal. However, infants with a jejunoileal stenosis typically have failure to thrive, which becomes evident with time, and ultimately the stenotic region of bowel progresses to complete intestinal obstruction.

Diagnosis

In the neonatal period the diagnosis of jejunoileal atresia can usually be made with a plain abdominal film without the need for an iodinated oral contrast agent such as gastrografin or barium; if jejunoileal atresia is present, swallowed air serves as a contrast agent. In neonates with intestinal obstruction, swallowed air reaches the proximal bowel within 1 hour and the distal small bowel within 3 hours. Timing may be delayed in premature or sick infants with poor sucking. ^, Features of jejunoileal atresia on abdominal x-ray include the presence of distended gas-filled and fluid-filled proximal loops of small bowel and the absence of distal bowel gas ( Fig. 28.17 ). If jejunoileal atresia is associated with cystic fibrosis, fewer air–fluid levels are evident, and the typical ground-glass appearance of inspissated meconium is seen. A small bowel follow through with limited oral iodinated contrast study may be useful in cases of suspected intestinal stenosis.

(A) The abdominal radiograph in this neonate shows several proximally dilated intestinal loops consistent with jejunal atresia. (B) A type III(a) distal atresia was found at operation.

In radiographic cases where multiple distended loops of bowel are present, a distal obstruction is suspected either in the ileum or colon; in these cases, a rectal contrast study is warranted. As haustral markings are rarely seen in neonates, distal ileal atresia may be difficult to differentiate from colonic atresia ( Fig. 28.18 ). With ileal atresia a contrast enema typically reveals a patent colon; however, the colon will appear unused and decompressed. In distal atresias, obtaining a preoperative barium enema is important as intraoperative anterograde injections of saline into the large bowel may fail to identify an associated colonic or rectal atresia. ^, If the small-bowel atresia occurred late in gestation, the bowel distal to the atresia may have a more normal caliber. Occasionally, air and meconium can accumulate proximal to an atresia, mimicking the radiologic appearance of meconium ileus. Total colonic aganglionosis may also be difficult to differentiate from small-bowel atresia.

The diagnosis of colonic atresia can be difficult on the plain abdominal radiograph. This radiograph shows multiple dilated intestinal loops and appears similar to the findings shown in Fig. 28.14 . At operation, the infant was found to have atresia of the transverse colon (see Fig. 28.16 ).

Ten percent of babies with jejunoileal atresia present with meconium peritonitis. The intestinal perforation usually occurs proximal to the obstruction, near the bulbous portion of proximal bowel. In these neonates the radiologic appearance of a meconium pseudocyst containing a large air–fluid level is often present and related to the late intrauterine bowel perforation. Intraluminal calcification of meconium or intramural calcification in the form of diffuse punctate or rounded aggregations have been reported with intestinal stenosis or atresia. Meconium calcification in patients with FMIA produces a “string of pearls,” which is pathognomonic of this condition. ^,

The clinical and radiologic findings of jejunoileal stenosis are determined by the location and degree of stenotic small bowel. The diagnosis of jejunoileal stenosis may be delayed for years due to the nonspecific presentation. Morphologic and functional changes in the bowel proximal to the stenosis vary depending on the degree of obstruction.

The first-line treatment of jejunoileal atresia is operative management with the establishment of small-bowel continuity or creation of a double-barrel enterostomy, with or without bowel resection. The timing of the diagnosis of jejunoileal atresia is critical as a delay (in cases of ischemic bowel) may result in impaired intestinal viability, frank necrosis and perforation, fluid and electrolyte abnormalities, sepsis, and mortality. Preoperative management should include gastric decompression and fluid resuscitation to correct electrolyte and acid–base abnormalities and hypovolemia. Antibiotics should be initiated if there is suspicion for perforation or infection.

Management Considerations

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