Overview: Duodenal atresia and stenosis represent a spectrum ranging from complete to partial obstruction, presenting from prenatal life to late childhood or even adulthood. The incidence of duodenal atresia or stenosis is cited as approximately 1 : 7000 live births and represents nearly half of intestinal atresias.1,2 Similar to atresia of the more distal bowel, duodenal atresia is classified as types I through III. Type I atresias consist of a completely or partially obstructing membrane, type II atresias are connected by a fibrous cord, and type III atresias are separated by a gap. The duodenal diverticulum or “windsock” duodenum is considered a variant of type I atresia.³

Etiology: The lumen of the duodenum is obliterated during the fourth to sixth weeks of gestation because of rapid cell division and normally recanalizes by the twelfth week. The etiology of duodenal atresia and stenosis is believed to be the result of failure of recanalization of the lumen of the duodenum.4,5

Clinical Presentation: Presentation may occur prenatally with polyhydramnios, which occurs in approximately 30% to 50% of cases,3,5 and premature birth is seen in nearly half of patients.⁵ Approximately one third of cases of congenital duodenal obstruction presenting in the neonatal period are due to duodenal stenosis.⁵ Postnatally, infants with atresia typically present with vomiting within the first 24 hours of life. Because duodenal atresia/stenosis typically occurs distal to the ampulla of Vater, these patients will present with bilious vomiting. However, obstruction occurs proximal to the ampulla of Vater in as many as 23% of patients.^6,7 Such patients will present with nonbilious vomiting, simulating hypertrophic pyloric stenosis. Because duodenal obstruction is proximal, abdominal distension is not a typical finding, although fullness in the epigastric region may be present as a result of the dilated stomach and duodenum. Patients with duodenal stenosis may present later in life, depending on the degree of obstruction; presentation may be relatively nonspecific (such as failure to thrive), or it may present as pancreatitis as a result of reflux into the pancreatic duct, proximal to the site of obstruction.^8,9 Presentation may be precipitated by ingestion of a foreign body, which fails to pass and may exacerbate the degree of obstruction, leading to abdominal pain and/or vomiting.¹⁰ In patients with a duodenal diaphragm, an intraluminal duodenal diverticulum or “windsock” may be found, and presentation also may be precipitated by ingestion of a foreign body.¹¹

Associated anomalies are common in patients with duodenal atresia/stenosis and may be responsible for presenting signs and symptoms. Annular pancreas and malrotation are seen in approximately one third of cases.⁵ Trisomy 21 is present in approximately 25% to 40% of infants with duodenal atresia/stenosis; conversely, approximately 4% of infants with Down syndrome have duodenal obstruction.^5,12 Hirschsprung disease has been reported in approximately 1% to 3% of patients with duodenal atresia and Down syndrome.^13,14 Duodenal atresia may be seen in approximately 5% of patients with esophageal atresia with or without a fistula.¹⁵ Heterotaxy with polysplenia has been reported in patients with duodenal diaphragm/intraluminal diverticulum.^8,16

Imaging: Abdominal radiographs are the starting point in the evaluation of a child with suspected obstruction. In the neonate with duodenal atresia, the abdominal radiograph demonstrates the classic “double bubble appearance,” representing the dilated stomach and duodenum.17,18 Because obstruction has been present in utero, the obstructed proximal duodenum is typically large, approximately one half to one third the size of the stomach (Fig. 103-1); at times the pylorus is wide open, and the two bubbles are not distinctly separated (see Fig. 103-1, B). This appearance on the abdominal radiograph is diagnostic, and contrast studies to confirm the diagnosis are not needed. Rarely, air can be seen distally in a patient with complete atresia; this occurs when the atresia is flanked by the branches of an anomalous bifid common bile duct, with separate insertions into the duodenum above and below the point of atresia. Air or contrast material may be seen refluxing into the anomalous ducts, which allow the contents of the obstructed proximal duodenum to course into the distal duodenum, bypassing the point of obstruction (Fig. 103-2).^7,19 In patients with duodenal stenosis, dilatation of the stomach and proximal duodenum and decrease in distal gas is seen commensurate with the degree of obstruction. If the stenosis is mild or the stomach is decompressed via an enteric tube, the plain abdominal radiographs may be nonrevealing (e-Fig. 103-3). In patients with duodenal atresia associated with esophageal atresia with a fistula, plain films are diagnostic (Fig. 103-4).

An upper gastrointestinal (GI) series may be needed in patients with duodenal stenosis or in cases in which differentiation from malrotation is a concern. Furthermore, malrotation can coexist with duodenal stenosis or atresia (e-Fig. 103-5).²⁰ Therefore if any clinical concern for malrotation exists or if surgery is to be delayed, an upper GI series is indicated. In patients with duodenal atresia, contrast enema has been performed in the past to assess the rotation of the bowel, but this examination is not helpful if it is normal or if the cecum is high-riding.^21,22

In patients with duodenal stenosis, an upper GI series will confirm the partial obstruction (Fig. 103-6); when a web is present, the membrane may be seen as a thin linear filling defect (see Fig. 103-6, B and C). A duodenal diverticulum is more conspicuous, particularly when underscored by an ingested foreign body (e-Fig. 103-7). In patients with duodenal atresia simulating duodenal stenosis as a result of bypass of the obstruction by anomalous ducts, contrast may be seen within the ducts, as previously discussed (see Fig. 103-2).

Cross-sectional imaging currently does not have a routine place in evaluation of patients with duodenal atresia or stenosis. However, occasionally a patient with duodenal stenosis proximal to the ampulla of Vater will present with nonbilious vomiting and come to ultrasound with a primary concern of pyloric stenosis. In those cases, ultrasound will reveal an abnormally distended pylorus and dilatation of the duodenal bulb (Fig. 103-8).

Treatment: Treatment of duodenal atresia and symptomatic duodenal stenosis is surgical repair. At the time when Ladd reported surgical correction of duodenal obstruction in 1932,²³ the reported mortality rate was approximately 40%.²⁴ In 1990, Kimura et al. described the technique of diamond-shaped anastomosis, which has become the standard procedure for open repair, with reported mortality of 5% to 10%, largely due to associated anomalies, particularly those involving cardiac lesions.^24,25 More recently, laparoscopic duodenoduodenostomy has been introduced with increasingly good results and reported improvement in return of bowel function, leading to reduced length of hospital stay.^24,26

Overview: Annular pancreas refers to encirclement of the descending portion of the duodenum by the pancreatic head. The prevalence of annular pancreas is not known, because asymptomatic cases are not always identified. Autopsy prevalence varies between 1 to 15 : 100,000 adults, whereas endoscopic retrograde cholangiopancreatography (ERCP) studies report 1 to 4 : 1000 among symptomatic patients.27,28 In children the incidence is estimated at approximately 1 to 12 : 15,000 births.²⁹ Annular pancreas may result in extrinsic duodenal obstruction; however, most cases of duodenal obstruction with annular pancreas are most likely the result of an associated intrinsic duodenal abnormality.³

Etiology: The pancreas arises as a small ventral and a larger dorsal bud from the duodenum. Normally the ventral bud rotates and fuses with the dorsal bud. When the ventral bud becomes tethered to the duodenum prior to rotation, or if the ventral bud fails to rotate completely before fusion, the result is an annular pancreas.3,28,30 The pancreatic annulus, the portion surrounding the duodenum, frequently has a separate duct entering the duodenum, opposite the ampulla of Vater. Duodenal contents may reflux through this duct into the annulus.

Clinical Presentation: Annular pancreas may be asymptomatic, and adult presentation has been reported (median age of 47 years) with signs and symptoms consistent with neoplasm, jaundice due to obstruction of the common bile duct, or pancreatitis, because duodenal contents may reflux through a separate pancreatic duct into the annulus.28,31 Pediatric patients typically present at a median age of 1 day at diagnosis with findings related to duodenal obstruction, which are either revealed at prenatal sonography or manifested as vomiting or feeding intolerance soon after birth.²⁸ Older pediatric patients can present with pancreatitis and jaundice.

Associated anomalies are common in children and include malrotation, esophageal atresia, anal atresia, and cardiac defects, particularly in patients with trisomy 21 and Cornelia de Lange syndrome12,28; annular pancreas also has been reported in patients with heterotaxy.³²

Imaging: Plain radiographs show findings of duodenal dilatation in patients who have an obstruction. An upper GI series will show narrowing of the descending portion of the duodenum (Fig. 103-9, A). Ultrasound may show a ring of pancreatic tissue about the descending portion of the duodenum, although the duodenum might be difficult to follow, and the appearance may resemble a mass at the level of the head of the pancreas (Fig. 103-9, B). A more definitive diagnosis can be made with computed tomography (CT; Fig. 103-9, C to E). Magnetic resonance imaging (MRI) also may show the ring of pancreatic tissue, but MR cholangiopancreatography will show more definitive findings, outlining the annular course of the pancreatic ducts (see Fig. 103-9 F and G), analogous to the findings seen with endoscopic retrograde cholangiopancreatography (e-Fig. 103-10).

Treatment: As in the case of intrinsic duodenal obstruction, treatment is surgical bypass; interruption or division of the pancreatic tissue around the duodenum is not indicated because of the likelihood of postoperative leakage or pancreatitis.³

Acute Volvulus: In persons with volvulus, the duodenum rotates, typically clockwise, about the axis of the superior mesenteric artery (Fig. 103-14) and is obstructed at its third portion, distal to the ampulla of Vater. Because approximately 60% to 80% of patients with volvulus present in the first month of life,^{33,34,38,43,44} the typical presentation is that of a previously well neonate who experiences the sudden onset of bilious vomiting. The infant may experience crampy abdominal pain, which could be confused with colic. If the obstruction is significant, the abdomen may become initially scaphoid after distal intestinal contents are evacuated. Vascular compromise may lead to intraluminal bleeding and hematochezia, seen in 10% to 15% of patients with volvulus.³⁷ As ischemia of the midgut supervenes, the abdomen becomes distended and firm, with physical signs of peritonitis, and the patient will present in shock with cardiovascular collapse.³⁴

Chronic Volvulus: Partial or intermittent volvulus tends to present more insidiously, with an average duration of symptoms of 28 months or greater before the correct diagnosis is made.³⁴ The patient usually has a history of abdominal pain, which can be severe but often is vague and intermittent, and often is associated with intermittent vomiting and/or failure to thrive. Impairment of venous and lymphatic flow leads to signs and symptoms of malabsorption.^45,46 The correct diagnosis is frequently delayed, with interim diagnoses including central or psychogenic vomiting, milk or other food allergies, and various malabsorption syndromes, such as celiac disease.^20,34,47,48

Ladd Bands: Patients with duodenal obstruction as a result of Ladd bands may present acutely, with sudden onset of bilious vomiting, or they may present with more chronic symptoms, with failure to thrive and intermittent abdominal pain.³⁴

Internal Hernias: Either right or left mesocolic or paraduodenal hernias produce symptoms by entrapment of bowel, which can produce partial or complete obstruction and may progress to ischemia and necrosis of bowel. Symptoms therefore consist of abdominal pain and vomiting.

Upper GI Series: An upper GI series is at present considered the standard examination to evaluate for malrotation and for its complications, particularly volvulus.

Documentation of normally rotated bowel can be challenging, and technique is very important. In pediatric patients, documentation of the normally rotated C-loop needs to be made on passage of the first bolus of contrast from the stomach; missing this opportunity can result in confusing and misleading findings. The course of the duodenum must be documented in both frontal and lateral projections, because the lateral view is essential to document the retroperitoneal position of both ascending and descending portions.37,54 The duodenojejunal junction, recognized by an acute flexure as the duodenum returns to the peritoneal cavity, should be located to the left of the left pedicle at the same craniocaudal level as the duodenal bulb. The lateral view should show ascending and descending portions entirely superimposed anterior to the spine; anterior deviation of the descending limb is abnormal. The technique is discussed in Chapter 85. When malrotation with volvulus is suspected, we typically will use a low-osmolality water-soluble agent and position an enteric tube distally within the stomach to improve control over the first bolus. The fluoro-grab function of most current fluoroscopes allows movielike documentation of the progress of the first bolus through the duodenum without additional radiation dose, and it can be very helpful in confirming normal rotation, as well as in sorting out difficult cases and normal duodenal variants. The radiologist should be familiar with normal variants such as duodenum inversum, in which the duodenum shows a parallel ascending and descending course to the right of the spine, before crossing to the left and emerging into the peritoneal cavity at a normally positioned ligament of Treitz (Fig. 103-16, Video 103-1).⁵⁵ Conversely, it is imperative that an abnormal course of the duodenum in patients without volvulus be recognized, including abnormal location of the duodenojejunal junction on the frontal image (see Fig. 103-16, C) and an abnormally anterior course of all or part of the duodenum on the lateral view. Abnormal location of the duodenojejunal junction—“excessive redundancy of the duodenum to the right of the spine”—may be indicative of malrotation⁵⁵ and other findings, such as position of the duodenum on the lateral view, position of the cecum, and cross-sectional imaging may need to be considered.

In symptomatic patients with malrotation, the upper GI examination may reveal the volvulus itself, presenting a spiral twisting of the duodenum (classically described as a “corkscrew”) as it wraps around the axis of the superior mesenteric artery (see Fig. 103-16, D). When complete obstruction is present, the contrast column may terminate in a beaklike configuration as the contrast is propelled into the entrance of the spiral but cannot proceed further (see Fig. 103-16, E).

In patients with obstruction resulting from Ladd bands, the duodenum may demonstrate a kinked configuration (see Fig. 103-16, F) that at times resembles a Z-shape instead of the normal C-loop. The Z-shape is the result of tacking down and kinking of the duodenum by the abnormal attempts at fixation and at times may be very difficult to differentiate from volvulus.

Contrast Enema: Barium enema had been advocated by surgeons and radiologists in the investigation of patients suspected of malrotation and volvulus, in the belief that cecal position would define the presence or absence of malrotation while avoiding introduction of barium contrast proximal to the obstructed duodenum.20,56 However, with the understanding that up to 30% of patients with malrotation and its complications could have a normally rotated cecum, and with the realization that a high-riding cecum in a neonate may in fact be normally rotated,^20,57,58 the contrast enema is no longer considered the main fluoroscopic diagnostic tool in the investigation of these patients. Follow-through small bowel to evaluate the cecum when the upper GI series shows confusing findings has been advocated and may be helpful in some cases, but the previous problems are not obviated. The cecum itself may be very difficult to define if the appendix does not fill, and a colonic segment in the right lower quadrant may be mistaken for the cecum. However, a clearly abnormal cecal position, especially in children with an equivocal location of the duodenal-jejunal flexure, is diagnostic of malrotation.

Overview: A clearly abnormal course of the duodenum renders the diagnosis of malrotation straightforward (see Fig. 103-16, C). Unfortunately, subtle cases exist that lead to false-negative interpretations, and as previously discussed, normal variants may lead to false-positive results. In a retrospective review of 163 patients with surgically proven malrotation, upper GI examination had a sensitivity of 96%, with seven false-negative examinations.⁵⁹ On the other hand, a 15% false-positive diagnosis by upper GI examination, as demonstrated on subsequent surgical findings, also has been reported.⁶⁰ The frontal course of the duodenum may be misleading if the duodenojejunal flexure occurs over rather than to the left of the pedicle of the spine, if it occurs below the plane of the duodenal bulb, or if abnormal redundancy of the course of the duodenum occurs. The duodenojejunal junction also can be displaced by postoperative changes after liver transplantation,⁶¹ peritoneal masses, or abnormal, dilated bowel loops.⁶² Limitations of the lateral view include the fact that the aorta and the superior mesenteric artery are not visualized, and therefore true retroperitoneal position of the duodenum cannot be ascertained unequivocally, despite the parallel course of its ascending and descending portions anterior to the spine.²²

Interpretative Errors: False-positive interpretations usually result from failure to recognize normal variants or from displacement of a normal ligament of Treitz. Position of the proximal small bowel in the right upper quadrant, as an isolated finding, is not indicative of malrotation.55,59 We know that the neonatal duodenum is mobile.⁵⁸ Therefore in patients in whom there is internal traction upon the duodenum, such as infants with dilatation of bowel, the duodenojejunal junction may appear abnormally located on the upper GI examination.⁶² Normal variants of duodenal course, such as duodenum inversum (see Fig. 103-16, A and B, and Video 103-1) or redundant duodenum, also may lead to false-positive interpretations, although marked redundancy of the duodenum also can be a sign of malrotation.⁵⁵ Analysis of the true lateral view, or correlation with cross-sectional information, may be needed in some of these cases. A high position of the cecum or a mobile cecum, particularly in a neonate, also are typically normal findings but make evaluation for malrotation particularly challenging in individual patients.

Potential false-negative outcomes may result from suboptimal technique, such as failing to delineate the course of the duodenum on the first bolus of contrast from the stomach or from misinterpretation of the subtle finding of malrotation, such as kinking of the duodenum along its course or location of the duodenojejunal junction abnormally low or to the right of the left pedicle of the spine.21,37,54,58,59 A proposed scoring system whereby the presence of three of nine potential findings would indicate malrotation, whereas one of nine was considered normal and two of nine was considered indeterminate, has not met with universal success.^55,58