Keywords

FormalPara Learning Objectives

  • To understand the strengths and limitations of the different imaging modalities used for examining the pediatric gastrointestinal tract.

  • To become familiar with the most frequent congenital and acquired pediatric gastrointestinal pathologies in which imaging plays an important role.

20.1 Introduction

Age is a key factor in the differential diagnosis of gastrointestinal (GI) pathology in children. In a variety of pediatric GI pathologies, imaging plays a major role.

In term neonates, congenital anomalies of the GI tract causing obstruction are at the forefront: atresia, intestinal malrotation with or without midgut volvulus, Hirschsprung’s disease, meconium plug syndrome, and meconium ileus. In the premature neonate, necrotizing enterocolitis can be a life-threatening complication.

Intussusception is the most common cause of obstruction in infants and young children. In older children and adolescents, focus lies on inflammatory bowel disease. Appendicitis can occur at any age although most frequently in children older than 5. Duplication cysts of the GI tract are most commonly situated at the distal ileum. They are usually detected on prenatal ultrasound and sometimes only later in life when causing obstruction.

Different imaging modalities can be used to image the GI tract. Plain films, ultrasound, and contrast studies are the principal imaging tools. CT and MRI are problem solvers and are used in a specific context, such as trauma, inflammatory bowel disease (IBD), diseases of the biliary tree, and tumoral pathology.

20.2 Imaging Techniques

20.2.1 Conventional Radiography

In children with GI disorders, conventional abdominal radiographs still play a significant role, frequently in conjunction with ultrasound. Delineation of bowel gas is extremely helpful in abdominal pathology. Calcifications can easily be detected. In neonates and young children, abdominal radiographs are typically performed in a supine position. Horizontal beam examination in supine or left side down decubitus position can be added to detect small quantities of free intraperitoneal air.

Air is visible in the newborn stomach after the first swallow. After 12 h, most of the small bowel should be filled with air and by 24 h, air should appear in the rectum.

Small children typically have air throughout the entire GI tract and small and large bowel are usually not distinguishable from each other, especially when distended.

20.2.2 Ultrasound

Ultrasound is the first-choice imaging modality for the initial evaluation of the GI tract in children. With high frequency transducers, a detailed view of the abdominal contents can be obtained. One can evaluate peristalsis in real-time and vascularization of the bowel wall and the mesentery can be assessed. The graded compression technique is used to eliminate overlying gas and to reduce the distance between the GI tract and the transducer. In infants with a painful belly, most of the abdomen can be visualized from the flanks.

20.2.3 Fluoroscopy with Contrast Agents

In practice, in most pediatric radiology departments, water-soluble, low-osmolar, isotonic contrast agents at body temperature are used for the evaluation of the anatomy of the upper and lower GI tract in small children. Hyperosmolar contrast agents can cause pulmonary edema when aspirated and should be avoided at all times for upper GI series.

20.2.4 Computed Tomography (CT)

CT is reserved for emergent indications such as blunt or penetrating trauma, in cases when neither ultrasound or MRI can be used to assess the abdomen or when findings are inconclusive. The use of CT should be limited as much as possible because of the deleterious effect of radiation exposure, especially in young children.

20.2.5 Magnetic Resonance Imaging

MRI is indicated in non-acute situations when ultrasound is inadequate and for mapping of IBD, anomalies and diseases of the biliary tree and tumoral pathology. In addition, MRI can also be used in the fetal period. For example, gastroschisis, omphalocele, congenital diaphragmatic hernia and multiple other abdominal abnormalities can be easily differentiated by fetal MRI.

Key Point

Conventional radiographs and ultrasound are the modalities of choice for initial imaging of the gastrointestinal tract in children.

20.3 Obstruction of the Upper Gastrointestinal Tract

20.3.1 Hypertrophic Pyloric Stenosis

The etiology of hypertrophic pyloric stenosis is unknown. It occurs in about 2–5 per 1000 infants in a male-to-female ratio of approximately 4:1 [1]. Children typically present at an age of 2–8 weeks, classically with frequent forceful (“projectile”) non-bilious vomiting, failure to thrive and even weight loss and dehydration. Ultrasound is the modality of choice to confirm the diagnosis of a hypertrophic pyloric muscle. Typical sonographic findings are [2] (Fig. 20.1):

  1. 1.

    Muscle thickness of >3 mm

  2. 2.

    Pyloric length of >15 mm

  3. 3.

    Protrusion of the mucosa into the distended gastric antrum

Fig. 20.1
A sonographic image of the abdomen of an infant with dark patches on the left and bottom right and arrows pointing to the pyloric muscle.

Hypertrophic pyloric stenosis in a 5-week-old infant presenting with projectile vomiting: Thickening of the pyloric muscle (>3 mm) between the arrows and an elongated pyloric canal

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Pylorospasm, a transient contraction of the pyloric channel can mimic pyloric stenosis but the change in aspect of the pylorus during the examination is the key differentiating finding [3].

Foveolar hyperplasia, usually prostaglandin-induced, also shows a thickened pyloric wall, however, here the mucosa is thickened and not the muscular layer [4].

20.3.2 Duodenal Atresia and Stenosis

The most common cause of complete duodenal obstruction in neonates is duodenal atresia, which is thought to be caused by incomplete recanalization during gestation. It occurs in about 1 in 10.000 newborns and is associated with Down syndrome as well as with numerous congenital anomalies [5]. In most cases, the atresia is distal to the ampulla of Vater and the main symptom is biliary vomiting, which usually occurs within the first 24 h after birth. If the atresia is proximal to the ampulla, children present with non-biliary vomiting.

Plain films classically show a “double bubble” sign, in which the largest bubble on the left represents the stomach, and the smaller bubble to its right represents air in the dilated duodenum proximal to the atresia (Fig. 20.2a, b). Distal to the obstruction, no or minimal intestinal gas is visible [6]. No further radiological examination is required, and treatment is surgical.

Fig. 20.2
Two radiographs of the distended abdomen of an infant. In A, two dark-shaded bubbles, and in B, three dark bubbles on the right and middle are exposed.

(a) Duodenal atresia in a newborn: abdominal radiograph showing a classic double bubble sign of an air-distended stomach and proximal duodenum. No intestinal gas is visible more distally. (b) Small bowel atresia in a newborn: abdominal radiograph showing a triple bubble appearance, suggestive of a jejunal atresia

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Potential causes of incomplete duodenal obstruction include duodenal stenosis, duodenal web, annular pancreas, midgut volvulus, and duplication cysts. Duodenal stenosis and duodenal web are radiologically difficult to differentiate. Radiography shows a distended stomach and duodenum filled with air, and little to normal amounts of air in the distal bowel. On fluoroscopy, duodenal web can exhibit the “windsock sign,” produced by intraluminal ballooning of a duodenal diverticulum, surrounded by a mucosal web [7].

Key Point

Hypertrophic pyloric stenosis is a common cause of gastric outlet obstruction in neonates and can be diagnosed using ultrasound. Duodenal obstruction in neonates is most commonly caused by duodenal atresia, which is seen as a “double bubble sign” on conventional radiography.

20.3.3 Malrotation and Midgut Volvulus

Malrotation is a spectrum of disorders regarding the embryological intestinal rotation and fixation. It is always present in congenital diaphragmatic hernia and anterior bowel wall defects, i.e., omphalocele and gastroschisis. It is found more frequently in combination with intestinal atresia and is 25 times more frequent in patients with trisomy 13, 18, and 21 [8]. Midgut volvulus is a life-threatening complication of malrotation and a surgical emergency occurring most frequently in neonates and young infants. Due to an abnormal fixation and a short mesenteric root, the small bowel rotates around the axis of the superior mesenteric artery (SMA). This volvulus leads to varying degrees of bowel obstruction, lymphatic and venous drainage obstruction, and may eventually compromise the arterial supply. Bilious vomiting should prompt emergent exclusion of malrotation, with or without midgut volvulus. Imaging is crucial, primarily ultrasound and upper GI series [9].

In case of volvulus, the visualization of the whirlpool sign (Fig. 20.3a) showing the clockwise rotation of the bowel and the superior mesenteric vein around the SMA, has a 100% sensitivity and specificity in symptomatic children. In the absence of volvulus, malrotation should be excluded because of the associated risk of volvulus. An abnormal position of the superior mesenteric vessels (in a normal situation, the artery lies left and posteriorly to the vein) can be found; however, it is neither strongly sensitive nor specific. A retroperitoneal position of the third part of the duodenum, on ultrasound identified between the SMA and the aorta, is a sign of normal rotation [9].

Fig. 20.3
A P E T image and an M R I of the abdomen focus on the malrotation of the midgut volvulus. The malrotation is highlighted in different colors at the center in image a. In b, a dark round patch on the top right is exposed.

(a) Malrotation with midgut volvulus in an infant: color Doppler shows a whirlpool-sign, the superior mesenteric vein and bowel rotating around the superior mesenteric artery. (b) Malrotation with midgut volvulus in another infant: on upper GI series, the typical corkscrew configuration of the twisted small bowel

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Detection of the position of the caecum is not helpful as it is normal in 30% of patients with malrotation and can be located in a high position in normal neonates [10].

With an upper GI series, midgut volvulus is seen as a spiral twisting of the duodenum in a corkscrew appearance (Fig. 20.3b) or a beak-like configuration in case of complete obstruction. In malrotation without volvulus, there is an abnormal position of the duodenum and the duodeno-jejunal junction. Obstruction can also be caused by ligaments (Ladd bands) crossing the duodenum.

Key Point

Malrotation is a congenital abnormality of the intestinal anatomy, with midgut volvulus as a life-threatening complication. The sonographic “whirlpool sign” confirms the diagnosis of volvulus, and retroperitoneal position of the duodenum is highly indicative of the absence of malrotation.

20.4 Obstruction of the Lower Intestinal Tract

20.4.1 Meconium Ileus and Ileal Atresia

Atresia is most common in the jejunum and ileum. It is thought to be due to a vascular accident in utero. Meconium ileus is an obstruction in the distal ileum due to thickened meconium. It is a frequent initial presentation of cystic fibrosis (CF) but is also seen in very low birth weight premature infants, infants of diabetic mothers, and babies born via cesarean section. It may be complicated by in utero bowel perforation. Meconium may then be free in the peritoneal cavity or become walled off in a rim-calcified meconium pseudocyst which can be delineated on conventional radiography and may also be seen with ultrasound.

Meconium peritonitis is not specific to meconium ileus: it occurs in any newborn with intrauterine intestinal perforation with intraperitoneal spillage of meconium for any reason, causing a sterile peritonitis and formation of dystrophic calcifications (Fig. 20.4a) [11].

Fig. 20.4
A C T image and an M R I of the abdomen in a and b, respectively. a. The distended abdomen with dark rounded bubbles of various sizes is exposed. b. A dark-shaded long segmented, twisted tube and a round patch on the left are indicated.

(a) Meconium peritonitis: multiple intraperitoneal calcifications after perforation in utero in a newborn with cystic fibrosis and meconium ileus. (b) Uncomplicated meconium ileus: contrast enema shows an unused microcolon and delineation of multiple meconium plugs in the terminal ileum

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In patients with distal intestinal obstruction, abdominal radiography will show gas-filled dilated bowel loops without gas in the rectum. In meconium ileus, the packed meconium can show a bubble soap appearance and intra-abdominal calcifications if in utero perforation has occurred. On contrast, enema a microcolon is seen, like in other causes of ileal obstruction, i.e., meconium ileus or long segment Hirschsprung’s disease (Fig. 20.4b).

In meconium ileus, a water-soluble moderately hyperosmolar contrast enema may be therapeutic by helping to evacuate the thickened meconium. Barium should be avoided to prevent a barium peritonitis in case of an intestinal perforation.

20.4.2 Meconium Plug Syndrome

This condition most often occurs in premature neonates and is sometimes described as small left colon or microcolon syndrome. It is associated with maternal diabetes, Hirschsprung’s disease and cystic fibrosis [12]. Clinically, distension of the abdomen and failure to pass meconium in the first weeks of life are the presenting symptoms and are caused by impacted meconium obstructing the left colon [13].

Conventional radiography is usually non-specific, showing mild to moderately dilated bowel loops with few to no fluid levels. Fluoroscopy is diagnostic for meconium plug syndrome, showing a small caliber of the left-sided colon and sometimes contrast filling defects due to the retained meconium. The rectum is commonly normal in size, unlike Hirschsprung’s disease, and the ascending and transverse colon also show a normal diameter with colonic haustrations. The iodine contrast administered during fluoroscopy often has additional therapeutic value as the laxative properties of the contrast medium can cause the patient to pass the meconium during or after the examination.

20.4.3 Hirschsprung’s Disease

In Hirschsprung’s disease, a variable length of distal bowel lacks ganglion cells and is unable to participate in normal peristaltic waves, resulting in a functional obstruction. The clinical presentation in neonates is one of distal obstruction, and failure to pass meconium in the first 24 h. Older children with Hirschsprung’s disease present with constipation, abdominal distension, vomiting, and failure to thrive in more severe cases.

In neonates, abdominal radiography demonstrates evidence of distal bowel obstruction, but there is usually gas in the rectum. The length of the aganglionic segment is variable, most commonly the transition between abnormal and normal bowel is at the rectosigmoid junction, but the distal part of the GI tract is always affected. Diagnosis is made by biopsy and contrast enema may help indicate the zone of transition.

Key Point

In obstructing conditions of the lower intestine such as ileal atresia, meconium ileus or plug, and Hirschsprung’s disease, conventional radiography can give an indication of obstruction location. Fluoroscopy as a next step has both diagnostic and therapeutic properties in meconium obstruction.

20.5 Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is an inflammation of the GI tract in neonates, particularly of preterm infants. The incidence varies between 0.3 and 2.4 infants/1000 births and between 3.9 and 22.4% among infants weighing less than 1500 g. It is the most common newborn surgical emergency. The pathogenesis of NEC is not completely understood, but there are strong suggestions that it is multifactorial: a combination of a genetic predisposition, intestinal immaturity, and an imbalance in microvascular tone, accompanied by a strong likelihood of abnormal microbial colonization in the intestine and a highly immunoreactive intestinal mucosa [14]. The risk factors are very low birth weight, prematurity, formula feeding, hypoxic–ischemic insults and infection. Term neonates with structural congenital heart defects asphyxia and babies from mothers using recreational drugs are also at risk. NEC can affect the intestines diffusely, but it typically affects segments of bowel and most frequently the terminal ileum and the proximal ascending colon. Abdominal radiography and ultrasound are used to diagnose NEC. Dilated bowel loops, focal intramural gas, portal venous gas, fixed bowel loops, paucity of bowel gas and pneumoperitoneum can be seen on abdominal radiography (Fig. 20.5a, b). With ultrasound, one can detect lack of peristalsis, bowel wall thickening or thinning, degree of bowel wall perfusion, intramural gas, ascites, and pneumoperitoneum [15, 16].

Fig. 20.5
Two radiographic images of the coronal and sagittal view of the abdomen focusing gas, respectively. A. The swollen abdomen with dark rounded bubbles of various sizes is exposed. B. A rod-shaped dark patch is indicated.

(a) Premature infant with necrotizing enterocolitis: abdominal radiograph shows extensive intramural gas as well as portal venous gas. (b) Premature infant with necrotizing enterocolitis: left colon on an abdominal radiograph with intramural gas

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Key Point

Necrotizing enterocolitis is a severe gastrointestinal inflammation seen most often in preterm neonates. Dilated and aperistaltic bowel loops, pneumo-peritoneum and intramural gas indicative of this surgical emergency can be detected on radiography and ultrasound.

20.6 Duplication Cysts

Intestinal duplication cysts are a rare entity, occurring in 0.2% of all children [17]. The etiology is unknown. Duplication cysts are associated with the presence of various other congenital anomalies. They can occur anywhere in the gastrointestinal tract. However, the most common location is in the distal ileum. The epithelial lining consists of gastric mucosa in up to one third of cases, which can sometimes lead to bleeding within the cyst. Most duplication cysts are detected prenatally or in the first year, after patients present with symptoms of gastrointestinal obstruction, and sometimes as a palpable mass or even as an intussusception.

Ultrasound is the preferred initial imaging technique. The imaging appearance of the cystic wall is usually thick compared to the bowel, and within the cyst often fluid-mucus level or blood after hemorrhage can be seen. Ultrasound characteristics that define a duplication cyst are the hyperechoic inner epithelial lining and a hypoechoic layer of smooth muscle within the wall. This typical double-layered appearance produces the classic “gut signature sign” (Fig. 20.6). The smooth muscle layer can also produce peristalsis within the cyst, which can be appreciated on ultrasound. Using the currently available high-resolution linear probes, the “five-layered cyst wall sign” can even be visualized, representing all wall layers normally seen in the gastrointestinal tract. Finally, duplication cysts always demonstrate a close relation with any part of the gastrointestinal tract, even when actual communication with the bowel cannot be visualized. On ultrasound, the “Y configuration” demonstrating a shared wall between the cyst and the intestine, is indicative of a duplication cyst. Subsequent MRI can provide more information on the anatomical relations in the workup for surgery, with the cyst usually showing a low T1 signal intensity and a high T2 signal intensity.

Fig. 20.6
An ultrasound image of the abdomen focusing on the dark rounded cyst at the center. A scale of 3.5 centimeters labeled B is illustrated on the right.

Prenatally detected abdominal cyst in a newborn: typical hypo-hyperechoic double layered wall of a duplication cyst, gut signature. The cyst contains echogenic debris and shares a wall with the bowel (B)

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The differential diagnoses include ovarian cyst, urachus cyst, mesenteric cyst, and lymphatic malformation. Treatment is surgical resection.

Key Point

Intestinal duplication cysts are characterized by their close relation with the gastrointestinal tract and their layered appearance similar to the intestine, which can be visualized using ultrasound.

20.7 Intussusception

In ileo-colic intussusception, the terminal ileum invaginates through the ileocecal valve into the cecum. This is the most common cause of small bowel obstruction in children and occurs most often in the first year of life, with a 2:1 male-to-female ratio [18, 19]. In most cases, the cause is idiopathic. This means that the lead point is hypertrophied lymphoid tissue which cannot clearly be visualized. In a minority of cases, usually older children, possible lead points include enlarged lymph nodes, Meckel’s diverticulum, duplication cyst, polyp, or diffuse bowel wall thickening caused by lymphoma or Henoch Schönlein purpura. The classic presentation of patients with intussusception is acute abdominal pain, vomiting, and bright red bloody or jelly-like stools although this triad is only present in less than 25% of patients [20].

Early diagnosis is essential to prevent bowel ischemia and perforation. The imaging method of choice in suspected intussusception is ultrasound. Typical ultrasound findings include the “donut sign” or “target sign” on transverse images of the bowel, and the “pseudo-kidney sign” on longitudinal images [21].

In patients with no signs of perforation, reduction of the intussusception can be done by an image-guided enema, pushing back the intussuscepted bowel segment with increasing intraluminal pressure. The most commonly used reduction methods are fluoroscopy-guided (with barium, water soluble contrast, or air) and ultrasound-guided (with water), the latter having the advantage that no ionizing radiation is used [20]. On ultrasound, the presence of dilated bowel loops indicating small bowel obstruction, and the presence of peritoneal fluid trapped between the intussuscepted bowel loops have been found to be predictors of unsuccessful outcome of reduction [22].

Key Point

In young infants, ileo-colic intussusception is mostly idiopathic, while in older children, a lead point is often the cause. The diagnosis is made by ultrasound, and fluoroscopy-guided or ultrasound-guided enema are the most commonly used methods for reduction of the intussusception.

20.8 Appendicitis

Appendicitis usually presents with abdominal pain, migrating from the periumbilical region to the right lower quadrant accompanied by fever and leukocytosis. However, one third of the children have atypical symptoms [23]. Ultrasound with graded compression is the preferred imaging modality for diagnosing pediatric appendicitis because of its high diagnostic accuracy and its noninvasive and nonradiating nature [24]. When ultrasound is not conclusive, MRI may be considered as an alternative modality.

An inflamed appendix is typically seen as a fluid-filled, non-compressible, blind-ending tubular structure with a diameter of 6 mm or more on longitudinal view and as a target image on transverse scan.

There may or may not be an appendicolith, pericecal, or periappendiceal fluid and enlarged mesenteric lymph nodes. Increased echogenicity of the periappendiceal fat is a useful sign. Differentiating perforated appendicitis from acute appendicitis prior to abscess formation is important: in the latter, management could be conservative. The constellation of dilated bowel, right lower quadrant echogenic fat, and complex fluid has a high specificity for perforated appendicitis.

Ruptured appendicitis can appear as a rounded structure with multiple rings that can very closely mimic the sonographic findings of intussusception [25]. Younger children and especially infants are at increased risk for perforation [26].

Key Point

Ultrasound is the imaging modality of choice in suspected appendicitis, showing an inflamed appendix, periappendiceal fluid, and inflamed fat. MRI may be an alternative imaging modality if ultrasound is non-conclusive. Infants are at increased risk for appendiceal perforation.

20.9 Inflammatory Bowel Disease

20.9.1 Crohn Disease

Crohn disease (CD) is the most common inflammatory small bowel disease. Presentation is usually above 10 years of age, with systemic symptoms such as weight loss, anorexia, malaise, and gastrointestinal symptoms like diarrhea and stools with blood and/or mucus. Any part of the GI tract can be involved, usually in a segmented distribution, but the terminal ileum and proximal colon are almost always affected. In children, there may be an isolated colonic involvement. Ultrasound and magnetic resonance enterography (MRE) are the preferred imaging methods [27,28,29].

In an early stage, the bowel wall is hypervascular and thickened in a concentric way with preservation of the wall stratification on ultrasound. The echogenicity of the surrounding mesentery is usually increased and also may show hyperemia. Mesenteric lymph nodes are typically increased in size and number. As the disease progresses, bowel wall stratification is lost and fibrosis develops. Fistula formation may occur, most commonly between cecum and terminal ileum.

20.9.2 Ulcerative Colitis

Ulcerative colitis is a less common idiopathic inflammatory bowel disease characteristically beginning in the rectum and extending proximally in a contiguous pattern, in contrast to CD. Bloody diarrhea and abdominal pain are frequent presenting features. Bowel wall is thickened, usually with preservation of the stratification [30].

Key Point

In children, Crohn disease is more common than ulcerative colitis. Ultrasound and MRE can display thickened bowel wall, hyperemic mesentery, and enlarged lymph nodes, followed by fibrosis in a later stage.

20.10 Concluding Remarks

There is a variety of GI pathology in the pediatric age group, and most of them are age-related. Several conditions can be live-threatening and need urgent action by the radiologist.

Take Home Messages

  • Conventional radiographs and ultrasound are the modalities of choice for initial imaging of the gastrointestinal tract in children.

  • Hypertrophic pyloric is diagnosed with ultrasound.

  • A “double bubble sign” on conventional radiography is seen in duodenal atresia.

  • The sonographic “whirlpool sign” confirms the diagnosis of volvulus, and a retroperitoneal position of the duodenum is highly indicative of the absence of malrotation.

  • In obstructing conditions of the lower intestine, conventional radiography can give an indication of the obstruction location.

  • Conventional radiography and ultrasound are the imaging modalities for necrotizing enterocolitis.

  • Intestinal duplication cysts are characterized by their close relation with the gastrointestinal tract and their layered appearance.

  • In older children with ileo-colic intussusception, a lead point has to be searched for.

  • Ultrasound is the imaging modality of choice in suspected appendicitis. Infants are at increased risk for appendiceal perforation.

  • Ultrasound and MRE are the modalities of choice to diagnose and monitor IBD in children.