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

Ultrasound: On ultrasound, as with other cross-sectional imaging, the relationship of the superior mesenteric artery and vein is readily evaluated. The superior mesenteric artery has a smaller size and surrounding hyperechoic halo and is located posterior and to the left of the superior mesenteric vein; identification can be confirmed with brief Doppler interrogation. This relationship was noted to be abnormal in patients with malrotation⁶³ but it is neither highly sensitive nor highly specific for malrotation with or without volvulus.⁶⁴

The “whirlpool” sign in patients with volvulus refers to a whirlpool-like appearance of the duodenum and superior mesenteric vein wrapped clockwise around the axis of the superior mesenteric artery.⁶⁵ In patients with this condition, a dilated duodenum can be followed as it enters into the volvulus (Fig. 103-17, A and E, and Video 103-2). It should be noted that this sign encompasses rotation of the duodenum, as well as the mesenteric vein. The sensitivity and specificity of the sonographic whirlpool sign has not been studied in large numbers of patients, but reports on smaller cohorts suggest that it is sensitive and specific for malrotation with volvulus.^66,67 It should be noted that this sign is not present in patients with malrotation without volvulus at the time of the examination and that it can be relatively subtle (Fig. 103-17, C and D, and Video 103-3). In older patients presenting with chronic volvulus, the sonographic findings are similar, although the duodenum may be considerably larger, because it has had a longer time to become dilated (Fig. 103-17, E and F, and Video 103-4).

The normal retroperitoneal course of the duodenum posterior to the superior mesenteric artery is an indication of normal rotation of the bowel; this course can be seen in cross-sectional imaging and has been underscored recently as an important finding on abdominal ultrasound.²²

CT is not the procedure of choice in evaluation of malrotation, but if it is performed for other reasons, the course of the duodenum and the position of the cecum should be assessed, and volvulus should be recognized if it is present (Fig. 103-18).

Treatment: The treatment for malrotation with volvulus consists of surgical detorsion, identification and lysis of Ladd bands, straightening of the duodenum along the right abdomen, and placement of the cecum in the left lower quadrant, thus broadening the base of the mesentery and creating a separation between the duodenojejunal junction and the cecum resembling nonrotation, with incidental appendectomy. This procedure, which bears his name, was described by Dr. Ladd, and remains the standard for patients with malrotation.23,68 A laparoscopic Ladd procedure can be performed, but it may be very difficult to perform in an acutely ill neonate with volvulus; it has also been suggeted that fewer postoperative adhesions in laparoscopic surgery may predispose to recurrent volvulus, although insufficient comparative data are available at this time.^69,70 When accompanied by volvulus, the surgery is emergent, and correction of existing metabolic and electrolyte derangements must be undertaken. When malrotation in the absence of volvulus is found in the older child or adult, surgery is indicated if the patient is symptomatic. The role of surgery versus conservative management in asymptomatic older patients with malrotation without volvulus, such as patients with heterotaxy,⁷¹ remains controversial.⁷²

Overview: The portal vein forms at the junction of the superior mesenteric and splenic veins, and its normal course is retropancreatic and retroduodenal. The preduodenal portal vein, first reported in 1921, courses anterior to the pancreas and duodenum; it is important because of its associated anomalies, but its major significance is surgical.⁷³

Etiology: A preduodenal portal vein is the result of abnormal resorption of segments of the paired embryonic vitelline veins and their connections (e-Fig. 103-19). Normally the upper communicating branch between the left and right vitelline veins persists, with resorption of the cephalad segment of the left vitelline vein, the caudal segment of the right vitelline vein, and of the lower communicating branch, resulting in the duodenum coursing ventral to the portal vein. The preduodenal portal vein results when the upper communicating branch is resorbed, with persistence of the lower communicating branch, which courses ventral to the duodenum; there is resorption of the left vitelline vein and persistence of the cranial portion of the right vitelline vein.^74,75

Clinical Presentation: The preduodenal portal vein is associated with conditions that cause duodenal obstruction, including duodenal web, annular pancreas, and malrotation. Therefore the major presenting symptom of patients with a preduodenal portal vein is duodenal obstruction, as a result of the associated anomaly in most cases.76,77 A preduodenal portal vein is highly associated with heterotaxy, particularly polysplenia.^53,78 Besides obstruction, the most important concern is inadvertent injury during surgery.^77,79 A preduodenal portal vein should be identified before surgery whenever possible, particularly in patients at risk for this anatomy, such as patients with polysplenia and biliary atresia.^51,53,80

Imaging: The preduodenal portal vein is well visualized with cross-sectional imaging. On ultrasound, the sagittal course of the superior mesenteric vein can be followed as it moves ventrally, over the pancreas, to enter the liver, ventral to both pancreas and duodenum (Fig. 103-20).^53,81 On CT and MRI, the findings are similar (Fig. 103-21).⁸²

Treatment: No treatment is necessary for an asymptomatic preduodenal portal vein. When the vein is associated with obstruction, bypass of the obstruction or correction of malrotation or Ladd bands is indicated.⁸³

Overview: Atresia and stenosis affect the jejunum and ileum more commonly than any other portion of the abdominal gastrointestinal tract: approximately 51% involve the jejunum and ileum, compared with the duodenum in 40% and the colon in approximately 9%.⁸⁴ The incidence of jejunoileal atresia ranges between one and three cases per 10,000 live births, depending on geographic location, with the incidence being greater in persons of European and African-American descent than in persons from Latin America. Small bowel atresias in the ileum occur distally in nearly two thirds of cases. In the jejunum this ratio is reversed, with nearly two thirds occurring proximally and one third distally. Atresia is much more common than stenosis, which accounts for only approximately 5% of cases,⁸⁵ particularly in the ileum.

Jejunoileal atresias have been subdivided into five types and subtypes84,86 (Fig. 103-22). Type I represents mucosal or membranous atresia, which is limited to luminal discontinuity. In type II, the blind ends of the bowel are connected by a fibrous cord, with continuity of the underlying mesentery. Type IIIa indicates discontinuity between the bowel ends with an adjacent mesenteric defect, whereas IIIb is long-segment atresia with a wide mesenteric defect, typically described as “apple peel,” “Christmas tree,” and “maypole” mesentery because of the appearance of the residual distal small bowel coiled around its tenuous vascular supply through retrograde flow via the ileocolic, right colic, or inferior mesenteric arteries.⁸⁷ Type IV refers to multiple atresias (e-Fig. 103-23).

Etiology: Unlike the duodenum, in which the etiology of atresia and stenosis is believed to be failure of recanalization, the most likely and accepted etiology in the jejunum, ileum, and colon is a vascular accident, the location and extent of which governs the location and severity of the resultant defect. Experimental data in multiple species undergoing prenatal ligation of mesenteric branches resulting in corresponding bowel atresias gives credence to this theory.85,88 More circumstantial evidence in humans includes the findings of lanugo and bile pigments distal to the point of atresia, indicating patency of the intestinal lumen beyond the point when recanalization of the gut had been completed.⁸⁹

Conditions that can result in prenatal gut ischemia include gastroschisis, intrauterine volvulus, intussusception, and internal hernias.⁹⁰ Atresias are found in patients who have undergone significant compression of bowel segments, such as incarceration in omphalocele or in tight gastroschisis defects. Signs of peritonitis have been found in up to 48% of patients with atresia.⁸⁵ Extensive “apple-peel” small bowel atresia is postulated to occur as a result of occlusion of the superior mesenteric artery distal to the origin of the right colic and ileocolic arteries (Fig. 103-24).

Clinical Presentation: Patients with intestinal atresia may present prenatally with polyhydramnios or postnatally with bilious vomiting, upper or generalized abdominal distension, jaundice, and abnormalities in passage of meconium.

The percentage of infants with polyhydramnios increases with more proximal atresia, because less bowel surface area is present to absorb swallowed amniotic fluid, and polyhydramnios is present in approximately 38% of patients with jejunal atresia. The percentage of patients presenting with bilious emesis postnatally also increases with more proximal atresia, seen in approximately 84% of patients with jejunal atresia. Jaundice occurs more often in patients with jejunal (32%) than ileal (20%) atresia. Most patients, though not all, fail to pass meconium in the first 24 hours of life. Patients with more proximal atresias may show some distension of the upper abdomen, but abdominal distension due to dilatation of multiple loops of bowel is the rule in patients with distal atresias. Infants with the apple-peel variant of intestinal atresia tend to be premature and have a low birth weight, and more than half are shown to have malrotation of the midgut.⁸⁵

Other anomalies outside of the gastrointestinal system may be present in nearly one third of patients, more often in patients with jejunal than with ileal atresia.⁹¹ Although duodenal atresia shows a high association with trisomy 21, this is not the case with jejunoileal atresia, which is seen in approximately 0.55% to 3% of patients with Down syndrome. Multiple atresias and the apple-peel variant of intestinal atresia can show a genetic pattern in some families, and apple-peel atresias have been reported with a constellation of other anomalies, including ocular abnormalities and microcephaly.⁹⁵

Imaging: Plain radiographs in patients with bowel obstruction will differ from the normal appearance of the bowel (Fig. 103-25). Patients with proximal atresias will show dilatation of the stomach, duodenum, and jejunum to the point of atresia, although the degree of dilatation may be decreased if decompression occurs via the enteric tube (Fig. 103-26). In patients with ileal atresia (Fig. 103-27), abdominal radiographs will reveal dilatation of multiple gas-filled loops of bowel, often with protuberance of the flanks and elevation of the hemidiaphragms. Unlike older infants and adults, in neonates it is not possible to distinguish small from large bowel, and dilated loops of small bowel distributed along the expected location of the colon can mimic a dilated colon.⁹² However, gas will not be found in the rectum (Fig. 103-27), a finding that can be optimized by obtaining a prone cross-table lateral radiograph. Patients with jejunal apple-peel atresia will have findings of proximal atresia (e-Fig. 103-28). In patients with jejunal stenosis, the findings will be similar, with distal gas and proximal dilatation dependent upon the degree of stenosis (e-Fig. 103-29). Ileal stenosis is much less common.

In patients with proximal jejunal atresia, plain films with the aforementioned findings are usually diagnostic. Upper GI examination will demonstrate the dilated stomach, duodenum, and small bowel to the point of first atresia (see Fig. 103-26). In patients with plain film findings of distal obstruction, fluoroscopic diagnosis is accomplished with contrast enema. In patients with distal obstruction, use water-soluble contrast material diluted to a near iso-osmolal concentration (see Chapter 85 for additional information on technique). In patients with ileal atresia, the contrast enema will reveal a very small, unused colon, known as a microcolon, whose lumen has not been distended by swallowed material or succus entericus. The differential diagnosis of microcolon is that of distal small bowel obstruction, ileal atresia, or meconium ileus. The differential overlaps with some cases of long-segment Hirschsprung disease. Meconium pellets typically are absent from the microcolon in patients with ileal atresia (see Fig. 103-27).

Treatment: The treatment and management of patients with jejunal and ileal atresia or stenosis is surgical. Although considerable morbidity still plagues the survivors of these abnormalities,⁹⁰ the prognosis of these infants has undergone revolutionary improvement. Survival has improved from approximately 1% to 10% in the first half of the twentieth century to 95% currently, related to improvement in surgical techniques, perioperative care, and nutritional support.⁹⁰

Overview: Meconium ileus is responsible for approximately 20% of neonatal intestinal obstruction and denotes an obstruction in the terminal ileum as a result of inspissated meconium.⁹³ Meconium ileus is the initial presentation in approximately 15% to 20% of patients with cystic fibrosis (CF). Although most patients who present with meconium ileus will be diagnosed with CF, exceptions have been reported, including patients with pancreatic insufficiency and patients with very long segment Hirschsprung disease encompassing the small bowel.^94–97 More recent reports suggest that a greater percentage of infants with meconium ileus might not have CF, but the underlying cause of distal small bowel obstruction in such infants is unknown.^95,98

Etiology: Patients with CF have a defect in the gene sited in locus q31.2 of chromosome 7, which encodes for the CF transmembrane conductance regulator (CTFR) protein and renders it ineffective in the regulation of chloride transport across cell membranes in lungs, liver, pancreas, skin, digestive, and reproductive tracts. In the fetal gut, abnormal secretory products of the intestinal epithelium result in meconium with an abnormal electrolyte environment and increased concentration of protein (particularly albumin), which interacts with other components of meconium, such as mucopolysaccharides, to form abnormally viscid and tenacious meconium. Degradation of this material is impeded by abnormal concentration of pancreatic enzymes, which also is the result of a defective CTFR protein.99,100 The meconium inspissates within the distal small bowel lumen, causing high-grade small bowel obstruction (Fig. 103-30).

Clinical Presentation: The presentation of infants with meconium ileus is one of distal bowel obstruction, which may be complicated by an in utero event leading to prenatal perforation. Patients with uncomplicated or simple meconium ileus may have been identified prenatally with abdominal distension, dilatation of bowel loops, and hyperechoic bowel.101–103 Approximately 20% of the infants demonstrate polyhydramnios in utero, more frequently in the subgroup with complicated meconium ileus. Postnatally they will present with abdominal distension, failure to pass meconium, and bilious vomiting.

Complicated meconium ileus occurs in approximately 40% to 50% of cases95,104 and results from an in utero event: the weight of the tenacious meconium can lead to a segmental volvulus, which in turn can lead to perforation with meconium peritonitis, resulting in a loculated meconium cyst or a small bowel atresia. The prenatal perforation may seal over in utero or may persist postnatally. By the age of 6 months, prognosis is similar to patients who did not present with meconium ileus.¹⁰⁴

Patients with CTFR G542X mutations have been reported to have a higher incidence of meconium ileus than do patients with other mutations, whereas complicated meconium ileus has been reported more frequently in patients homozygous for the classic ΔF508 mutation. Modifier genes located on chromosomes 4q35.1, 8p23.1, 11q25, and 19q13 also have been reported to affect the clinical presentation of infants with CF and the development of meconium ileus.⁹⁸

Meconium peritonitis is not specific to meconium ileus; it occurs in patients in whom an intrauterine perforation is present for any reason. Occasionally a child is born with intraperitoneal calcifications consistent with meconium peritonitis, in whom the perforation has sealed over, and who is otherwise well, with no definable clinical sequelae (Fig. 103-31, A).

Imaging: Radiographs of infants with complicated meconium ileus, in addition to signs of distal bowel obstruction, may show intraperitoneal calcifications consistent with meconium peritonitis and/or mass effect consistent with a meconium cyst (see Fig. 103-31, B to F). Patients with such signs of complicated meconium ileus are not candidates for contrast fluoroscopic evaluation of either the upper or lower GI tracts. However, ultrasound is useful in some infants with complicated meconium ileus to document the location and size of a suspected meconium cyst. Hyperechoic bowel loops, described in the fetus,^101–103 also may be seen postnatally (see Fig. 103-31, D).

In infants with no evidence of complicated meconium ileus, abdominal radiographs will show abdominal distension and multiple dilated loops of bowel, consistent with a distal obstruction (Fig. 103-32). In patients with meconium ileus, the ileal loops are packed with meconium, which often renders a characteristic “soap bubble” appearance, originally described by Neuhauser in 1946.¹⁰⁵ Air-fluid levels tend to be less conspicuous than in patients with ileal atresia,¹⁰⁶ although their presence does not negate the diagnosis.

Similar to patients with ileal atresia, diagnostic imaging evaluation starts from below with contrast enema. As previously discussed, the diagnostic examination begins with water-soluble contrast material diluted to a near iso-osmolal concentration. Barium is not recommended because barium inspissated within the tarry meconium is unlikely to prove helpful, and it is not necessary for diagnosis. Hyperosmolal material likewise will not be helpful if the diagnosis proves to be Hirschsprung disease (see Chapter 85 for additional information on technique). The examination will reveal a small colon, known as a microcolon, similar to that seen in patients with ileal atresia. However, in patients with meconium ileus, in whom the distal ileum is impacted with tarry, tenacious meconium, small meconium pellets may be seen within the microcolon (see Fig. 103-32, B). If contrast material refluxes into the distal ileum, meconium pellets may be identified; if contrast material reaches into the dilated loops of bowel, ileal atresia is excluded. However, contrast material may not reflux readily into the dilated bowel loops in patients with meconium ileus because of the inability to traverse the segments containing inspissated meconium; in such cases, final diagnosis is made at surgical intervention.

Treatment: Patients with complicated meconium ileus as revealed on clinical evaluation, findings of calcifications on abdominal radiographs or free intraperitoneal air, are managed surgically. An enema procedure has no role in these patients.

The mainstay of treatment for patients with simple meconium ileus initially was surgery, with enterotomy and intraoperative irrigation of the bowel to solubilize, disimpact, and remove the inspissated obstructing meconium.¹⁰⁷ Since the initial description by Noblett in 1969, the therapeutic Gastrograffin contrast enema often is the initial treatment in patients with uncomplicated meconium ileus. Its success has been attributed to the hyperosmolarity of the medium (1900 mOsm/L), as well as to the surfactant properties of polysorbate 80 (Tween 80).¹⁰⁸ Expected complications related to hyperosmolarity of the agent and subsequent fluid shifts can be managed with careful fluid and electrolyte monitoring and replacement after the enema procedure. Before the procedure, the patient likewise should be prepared for the enema with adequate fluid and electrolyte replacement, and surgical consultation and standby are imperative.

Subsequent investigators have reported problems with bowel necrosis after administration of the Gastrografin enema,⁴¹ ascribed to the polysorbate component, which has been found experimentally to cause mucosal damage and necrosis in experiments on animals.¹⁰⁹ For these reasons, many pediatric radiologists avoid use of Gastrografin and instead use other moderately hyperosmolar media. A survey of pediatric radiologists in North America, published in 1995, showed a higher success rate when an additive such as N-acetylcysteine (Mucomyst) was used but showed no correlation of success rate with osmolarity of the contrast medium used; the reported perforation rate was 2.75%, with a higher risk of perforation in cases in which balloon occlusion of the rectum was used.¹¹⁰

A therapeutic enema may need to be repeated for definitive resolution of the obstruction. Success may be dependent at least partly on the perseverance of the operator, because the contrast material does not easily advance beyond the obstructing meconium into the dilated loops of bowel. The overall success can vary between 0 and 100% in specific institutions¹¹⁰ but is reported to be between 50% and 65%.¹⁰⁴

Surgery is indicated for patients for whom the therapeutic enema is unsuccessful at relieving the bowel obstruction.

Overview: Meckel diverticulum is named after Johann Friedrich Meckel the younger, who was the first to report extensively on its embryology, anatomy, and clinical manifestations in the early nineteenth century. Meckel diverticulum is found in approximately 1% to 4% of the population and is located within 100 cm from the ileocecal junction.¹¹¹

Etiology: The Meckel diverticulum is a remnant of the vitelline or omphalomesenteric duct, the communication between the embryonic gut and the yolk sac. This duct normally obliterates by the fifth to seventh week of gestation. Approximately 25% of diverticula may have a persistent attachment to the abdominal wall, considered to represent a remnant of the left omphalomesenteric artery. In addition to a Meckel diverticulum with or without persistent attachment to the abdominal wall, remnants of the omphalomesenteric duct include patency of the duct presenting as an umbilicoileal fistula and fibrous vitelline cords connecting the ileum to the umbilicus, with or without a vitelline cyst along the length of the cord.112,113

Clinical Presentation: Most Meckel diverticula remain asymptomatic, with complication rates estimated at 4% to 6%, decreasing with age.113,114 Although the prevalence of diverticula is similar in both genders, symptoms are more likely to occur in males and in younger patients.^113,114 The most common clinical presentation is that of painless rectal bleeding. Meckel diverticulum accounts for approximately 50% of lower GI bleeding in infants and toddlers, typically occurring as a complication of gastric mucosa within the diverticulum. The incidence of gastric mucosa within bleeding Meckel diverticula is estimated at 23% to 80%.^112,113 Heterotopic pancreatic tissue is found in 5% to 16% of cases.¹¹³ In addition to bleeding, gastric and pancreatic mucosa can lead to inflammation of the diverticulum, with abdominal pain mimicking appendicitis, and which similarly can evolve into perforation and/or obstruction.^112,115,116

Meckel diverticulum can present as distal small bowel obstruction through a variety of other mechanisms. The diverticulum may invert into the ileal lumen and serve as a lead point for intussusception. If the diverticulum remains attached to the umbilicus, it can serve as an anchor for a segmental volvulus, or the fibrous cord can promote a bowel obstruction as an adhesion or as a closed loop obstruction. Volvulus also can occur with very large or “giant” diverticula. The Meckel diverticulum can become incarcerated in an inguinal hernia, known as a Littre hernia.¹¹³ Patients with obstruction present with abdominal pain and vomiting, which is complicated by bleeding in cases of intussusception.

Meckel diverticula also can present with neoplasia, typically in adult patients; the tumors are most commonly carcinoids, and complications include luminal obstruction and intussusception. Meckel diverticula may contain enteroliths and also may present with parasitic infections, such as ascariasis, and lodged ingested foreign bodies.¹¹²

Imaging: Plain films are not particularly helpful in the diagnosis of Meckel diverticula except as indicators of some of its complications, such as obstruction. Fluoroscopic examination such as small bowel follow-through requires very careful technique and may be able to demonstrate the antimesenteric saccular outpouch from the distal ileum, particularly when enteroclysis is performed, or when the diverticula are larger, such as the “giant” diverticula that measure greater than 5 to 6 cm in diameter and up to 15 cm in length.¹¹³ However, small diverticula may be inconspicuous and difficult to subtract from the multiple bowel loops in the background.

The most well-known imaging examination for detection of Meckel diverticula is the technetium pertechnetate abdominal scintigram (see Chapter 85).¹¹⁷ This examination is dependent upon the presence of gastric mucosa, with a reported sensitivity of 80% to 90%, a specificity of 95%, and accuracy of 90% in pediatric patients,¹¹⁸ although accuracy may be lower in patients who present with a hemoglobin <11 g/dL.¹¹⁷ Use of single photon emission CT has been reported to identify the Meckel diverticulum in some patients in whom conventional planar imaging is unsuccessful.¹¹³ Duplication cysts with gastric mucosa are part of the differential diagnosis of a positive scan but often can be differentiated clinically or with other cross-sectional imaging modalities.

In patients with inflamed diverticula, ultrasound and CT can detect the inflamed diverticulum, which appears as a blind-ending structure, surrounded by inflammation. On cross-sectional imaging the findings may be very difficult to distinguish from appendicitis in some cases; however, in other cases, a much larger size and periumbilical location may suggest the correct diagnosis preoperatively (Fig. 103-33). In patients in whom intussusception is present, the intussuscepted diverticulum is outlined by air during air enema reduction.¹¹⁹ Both ultrasound and CT may identify the intussuscepted, thick-walled, fluid-filled diverticulum within the intussusceptum complex.^113,120,121

Treatment: The treatment of complicated Meckel diverticula is surgical resection. However, the treatment of diverticula that are asymptomatic and incidentally discovered during surgery for another reason is less clear; the potential for the development of complications needs to be weighed against the potential for postsurgical complications, reported as 1% to 2% for patients with incidental resection, with a mortality rate of 0.001%.¹¹² Some authors advocate a judicious approach to this problem, taking into consideration higher risk factors for complications, such as younger age and male gender.¹²² Laparoscopic diagnosis and resection of symptomatic diverticula is currently advocated, with some investigators suggesting that laparoscopy can replace the Meckel technetium scan in patients with a high clinical suspicion of Meckel diverticulum as the bleeding source.^112,123

Overview: Duplication cysts of the GI tract are characterized by contiguity with and adherence to a segment of the alimentary tract, by a smooth muscle coat and mucosal lining including one or more types of cells found within any portion of the alimentary canal, and by a shared a blood supply with native GI structures.¹²⁴ They can occur anywhere along the length of the entire GI tract from the mouth to the anus and are most common near the terminal ileum.¹²⁵ Duplication cysts occur along the mesenteric border of the involved bowel loop, and therefore in the duodenum they are found medial to the descending limb or along its third portion; duodenal duplications account for approximately 6% of the total and thus are uncommon.¹²⁶ Most duplication cysts do not communicate with the intestinal lumen.

Etiology: The etiology of alimentary tract duplications is not certain, and no one single theory satisfactorily explains all instances of duplication anomalies. One theory holds that duplication cysts are the result of incomplete attempts at twinning, a theory that also suggests an explanation for duplications of other organs, such as the bladder and urethra. The split notochord theory suggests that there is herniation of a diverticulum of the foregut through a gap in the notochord; this theory is helpful in understanding duplications that are associated with anomalies of the spine. A third possibility theorizes that these anomalies are the result of diverticula that form during the recanalization stage of the bowel. A fourth hypothesis suggests that environmental factors, such as trauma or hypoxia, can induce the events that can result in an enteric duplication.¹²⁶

Clinical Presentation: The presentation of duplication cysts is usually related to their size, thus presenting with mass effect, palpable mass, obstruction, or localized volvulus, or to the type of mucosa in its lining because cysts containing gastric mucosa can ulcerate, bleed, and lead to inflammatory changes. Patients present with abdominal pain and vomiting. Mass effect by duplication cysts can lead to bilious or nonbilious vomiting, or the patients may present with weight loss and failure to thrive. Duodenal duplication cysts can lead to pancreatitis, possibly related to compression of the pancreatic duct,¹²⁷ and also have been reported to cause fluid accumulation within the lesser sac.¹²⁸ Duplication cysts may act as a fulcrum for segmental volvulus.¹²⁵ Those located in the terminal ileum and ileocecal valve may act as a lead point in intussusception and should be suspected when intussusception occurs in infants within the first 3 months of life.

Imaging: Plain radiographs are usually noncontributory but may demonstrate a soft tissue mass or evidence of obstruction if the cyst is large, particularly if it is located along the distal aspect of the stomach or the duodenum.

An upper GI series could be the first study obtained in a child presenting with vomiting; in cases of duplication cysts of the duodenum, the examination reveals a filling defect along the mesenteric wall of the duodenum or extrinsic compression (Fig. 103-34). Compression of the gastric outlet or of the first portion of the duodenum by the cyst has been described as a “beak” sign.¹²⁹ If focal communication occurs between the cyst and the duodenum, contrast material will enter the duplication.

Small bowel duplication cysts beyond the duodenum may present with obstruction, inflammation, intussusception, or a combination (e-Fig. 103-35; also see Chapter 108). Cross-sectional imaging can confirm the diagnosis of a duplication cyst suspected from a prior study, or it may be the initial imaging modality used. Ultrasound typically reveals an anechoic cyst, but the fluid may contain debris if there has been infection or hemorrhage from associated ectopic gastric mucosa and ulceration. The typical “bowel wall signature” of an enteric duplication cyst is usually present.^130–132 The presence of bowel wall signature may help to differentiate a duodenal duplication cyst from a pancreatic pseudocyst. However, the gut signature is not completely sensitive or specific to duplication cysts; the gut signature may be obliterated by superimposed inflammatory changes and may be seen in other conditions, such as mesenteric cyst, cystic teratoma,¹³³ and ovarian cysts.

CT demonstrates a discrete fluid-filled cyst on the mesenteric border of the involved bowel segment, often with contrast enhancement of the cyst wall. On MRI, hemorrhage or infection can alter the signal characteristics of the cyst on water-sensitive sequences. MRI is particularly helpful in cases of duodenal duplication cyst, where MR cholangiopancreatography can demonstrate the relationship of the cyst to the duodenal wall, the pancreatic head, and the pancreatic and biliary ductal systems, which is important preoperative information for the surgeon.¹²⁶

Treatment: The most common treatment for duplication cysts is resection, although marsupialization with internal drainage also may be performed. Cysts with gastric mucosa should be excised or stripped of the mucosal lining; complex cases may require more extensive surgical excision.¹²⁶

Overview: Abdominal lymphatic malformations can be located in the mesentery or omentum as mesenteric or omental cysts. Lymphatic malformations have only an endothelial lining, are usually multiloculated, and may contain chyle. Most lymphatic malformations occur in the mesentery rather than the omentum because of its richer lymphatic content, most commonly in the ileal mesentery.134,135 Such cysts of lymphatic origin are lined by flat endothelial cells and contain lymphoid tissue within their walls.

Mesothelial cysts, on the other hand, occur in the small bowel, the mesentery, and the mesocolon and are the result of accumulation of fluid between mesothelial layers. They are lined by mesothelium, without mural muscle fibers or lymphatic structures.¹³⁶ Nonpancreatic pseudocysts also may occur in the mesentery, or more often in the omentum, and are believed to result from prior trauma or infection, with no inner cellular lining on histology.

Etiology: The etiology of lymphatic malformations and lymphatic mesenteric and omental cysts is not known; hypotheses include failure of embryonic lymphatic spaces to develop normal connections and drainage into the venous system, and benign proliferation of ectopic lymphatics sequestered from the venous system.¹³⁴

Clinical Presentation: Abdominal lymphatic malformations are rare, representing approximately 5% of all such malformations, and with a quoted prevalence of approximately 1 per 20,000 admissions at a children’s hospital, with a lower incidence in African Americans.134,137 In children, presentation is more common in boys, although in adults the presentation is more common in women, through a putative estrogenic effect.¹³⁸ These lesions may be asymptomatic and discovered incidentally, or they may present as a result of size or complications of the lesion. Mass effect can result in the development of partial obstruction over time or acutely as a result of acute enlargement of the cyst secondary to hemorrhage. Abdominal pain can occur through torsion of the cyst or one of its components (Fig. 103-36) or torsion of adjacent bowel loops with the cyst acting as a fulcrum. Cysts can become infected, producing fever, abdominal pain, or sepsis.^134,135

Imaging: Plain radiographs may show a large mass displacing intestinal loops. Dilated loops may be seen in patients with obstruction. Upper GI contrast studies show displacement of bowel with no communication. Ultrasound demonstrates the multilocular nature of the mass with fine septations (see Fig. 103-36). Most of the mass is anechoic, but some of the loculated spaces may have internal echogenicity, depending on the chyle or blood content.¹³⁹ On CT the attenuation values of the fluid range from near fat to near water, depending on its composition. On CT, septa and loculations are usually demonstrated, unless their attenuation value merges with that of the surrounding fluid in scans performed without contrast material; septa may enhance with injection of intravenous contrast material. Fine calcifications may be present in some cases.¹³⁴ MRI of lymphatic malformations shows characteristics of the cyst ranging from fluid with low-intensity signal on T1-weighted images to fat with high-intensity signal.¹⁴⁰

Treatment: Traditional treatment is surgical resection with complete extirpation of the cyst, although percutaneous drainage and sclerotherapy is a reasonable alternative in some cases. In children with mesenteric cysts, treatment is more likely to require segmental bowel resection than in adults (50% to 60% vs. 33%).¹³⁴ If complete resection is not possible, marsupialization of the cyst with sclerosis of the lining can be performed. A surgical classification of mesenteric cysts, based on operative management, includes four types: type 1 is on a pedicle, and easily removed, although more likely to undergo torsion. Type 2 is sessile and restricted to the mesenteric boundaries, whereas type 3 has retroperitoneal extension, representing an increased surgical challenge. Type 4 refers to multicentric cysts.¹³⁷

Laparoscopic resection is possible; however, this technique is best approached with caution because of relatively limited experience, if the diagnosis is not certain preoperatively, or if the procedure will necessitate segmental bowel resection.141–143