The stomach develops from the distal part of the embryonic foregut. The dorsal aspect of the primitive stomach grows faster than the ventral aspect, resulting in its asymmetric configuration. There is approximately 90° of clockwise rotation, such that the shorter ventral border moves to the right and the longer dorsal border (greater curvature) moves to the left. During this rotation, the cranial aspect of the developing stomach (the fundus) moves to the left and the caudal aspect (antrum) moves to the right and superiorly. The dorsal mesentery (dorsal mesogastrium) is carried to the left as the stomach rotates, thereby forming the boundary of the lesser sac of the peritoneum. The embryonic ventral mesentery attaches the stomach to the abdominal wall and liver. Alterations in this developmental sequence of gastric rotation and fixation cause the various forms of gastric malrotation.
Gastric malrotation refers to a spectrum of abnormalities in which 1 portion of the stomach is abnormally rotated around another. Deficient ligamentous fixation is the usual cause of rotational abnormalities of the stomach. There are 4 major anchoring ligaments of the stomach: the gastrohepatic, gastrophrenic, gastrosplenic, and gastrocolic ligaments. In addition, the distal portion of the stomach is relatively fixed by the retroperitoneal location of the duodenum. Rotational anomalies of the stomach are sometimes related to congenital malposition of the stomach (e.g., intrathoracic stomach) and/or congenital or acquired abnormalities of the diaphragm (e.g., congenital diaphragmatic hernia). There are rare reports of gastric volvulus in association with wandering spleen. In some instances of gastric malrotation, there is an acquired deficiency of gastric fixation due to prior surgery. About one-third of children with gastric volvulus have no known associated anomalies; this is termed primary or idiopathic volvulus.1–5
Rotational abnormalities of the stomach are classified as organoaxial and mesenteroaxial. Organoaxial rotation occurs around a line joining the hiatus and the pylorus. Mesenteroaxial rotation occurs around a line joining the greater and lesser curvatures. With gastric herniation through the esophageal hiatus, anterior organoaxial rotation is common. Deviation of the greater curvature is in an anterior and cephalad direction; this can be likened to the effect of twisting the distal aspect of the stomach in a counterclockwise direction. Posterior organoaxial rotation is uncommon. Mesenteroaxial rotation occurs along an axis 90° to the longitudinal axis. The stomach is flipped (“upside-down stomach”), with the antrum moving anteriorly and superiorly, and the greater curvature remaining on the left. Occasionally, there is rotation about both the organoaxial and mesenteroaxial axes; this is a combined volvulus. The term gastric volvulus refers to strangulation and obstruction of a malrotated stomach. By some definitions, volvulus refers to rotation of at least 180°, while gastric torsion indicates rotation of < 180°.6,7
Mesenteroaxial volvulus of the stomach sometimes presents as an abdominal catastrophe, because torsion of the stomach in this manner usually compromises the vascular supply. This type of rotational abnormality can occur in association with a large paraesophageal hernia, diaphragmatic eventration, or diaphragmatic hernia. The volvulus in a patient with mesenteroaxial rotation typically leads to the acute onset of severe epigastric pain and nonbilious vomiting. The vascular compromise can lead to gastric necrosis, perforation, and peritonitis. Less commonly, patients suffer chronic symptoms such as intermittent pain, abdominal distention, and failure to thrive.
With mesenteroaxial volvulus, a frontal abdominal radiograph with the patient in the supine position usually shows a distended fluid- and air-filled stomach with a spherical configuration. On the upright view, there are 2 air–fluid levels, 1 in the fundus inferiorly and the other in the antrum superiorly. The obstructed antrum is in a superior and medial position; the antrum sometimes has a beaked appearance. An abnormality of the diaphragm, such as a large eventration, is common. A fluoroscopic contrast study shows partial or complete obstruction at the gastroesophageal junction. If contrast enters the stomach, gastric outlet obstruction is also demonstrated.
Gastric organoaxial volvulus is uncommon in children. This most often occurs as a chronic abnormality in a patient with a large hiatal hernia. Chronic distention of the stomach with air, as occurs in some neurologically impaired children, may predispose to organoaxial rotation. Mild asymptomatic organoaxial rotation is common in infants and young children, and likely is due to ligamentous laxity. Symptomatic gastric outlet obstruction is relatively uncommon with organoaxial rotation. Contrast studies of organoaxial rotation show an inverted relationship of the greater and lesser curvatures of the stomach (Figure 35-1). The duodenal bulb is inferior to the antrum. The stomach frequently has an abnormal horizontal configuration. With marked rotation, the pyloric channel crosses the distal portion of the esophagus and the pylorus usually is directed inferiorly. An upright frontal abdominal radiograph may show a single long air–fluid level within the stomach.
| Pathology | Radiology |
|---|---|
| Gastric outlet obstruction | Stomach dilation |
| Mesenteroaxial malrotation | Antrum superior to fundus |
| Two gastric air–fluid levels on upright view | |
| Organoaxial malrotation | Inversion of greater and lesser curvatures |
| Horizontal configuration of stomach |
Pyloric atresia is a congenital complete obstruction of the outlet of the stomach. This lesion accounts for less than 1% of all atresias of the intestinal tract. About two-thirds of pyloric atresias are due to a web or thin diaphragm, that is, membranous atresia. In some patients, the web is incomplete, resulting in a form of congenital antral or pyloric stenosis. About one-third of children with pyloric atresia have a segmental lesion, with a fibrous band at the expected site of the lumen. Rarely, there is a complete segmental defect, with no connection between the separated ends of the stomach. The pathogenesis of most instances of pyloric atresia likely involves a localized vascular interruption during embryogenesis.
Pyloric atresia results in nonbilious vomiting, usually starting within several hours after birth. There is often a history of maternal polyhydramnios; evidence of gastric outlet obstruction is sometimes present on prenatal sonography. The abdomen of the newborn with pyloric atresia is usually scaphoid. However, gastric perforation can occur in these infants, in which case there is abdominal distension from intraperitoneal fluid. Aspiration pneumonia is an additional common complication of pyloric atresia. The clinical differential diagnosis of severe nonbilious vomiting in the newborn includes severe gastroesophageal reflux, congenital peritoneal bands, and hypertrophic pyloric stenosis. Duodenal obstruction (e.g., duodenal atresia) can overlap the clinical presentation of pyloric atresia, but typically leads to bilious vomiting.
Abdominal radiographs of the infant with pyloric atresia show distension of the stomach with air and fluid. There is no bowel gas distal to the stomach (Figure 35-2). Gastric dilation is lacking if perforation has occurred or the infant has recently vomited. Perforation leads to pneumoperitoneum and distention of the abdomen with free fluid. The findings on standard radiographs are usually sufficient for the diagnosis of pyloric atresia. A contrast evaluation of the stomach shows failure of contrast to pass beyond the pylorus. Depending on the nature of the obstruction (i.e., membranous or fibrous), the proximal aspect of the pylorus may or may not fill.
Congenital antral or pyloric stenosis represents an incomplete expression of similar pathology as occurs with pyloric atresia. Most often, the obstructing lesion is a web or diaphragm in the antrum. This may be a crescent-shaped web or a complete septum with a central opening. The web consists of a layer of mucosa overlying a smooth muscle component. The pathogenesis may involve an intrauterine insult that leads to focal ischemia. Rarely, the obstructing lesion is a constricted segment of the antrum.8,9
The clinical manifestations and age at presentation of congenital antral or pyloric stenosis vary with the severity of obstruction. When the obstruction is severe, the symptoms are similar to those of pyloric atresia, that is, neonatal nonbilious vomiting. Most often, however, the clinical presentation is delayed until the initiation of solid food in the diet. The findings are those of a partial gastric outlet obstruction, that is, vomiting, gastroesophageal reflux, and upper abdominal pain. Patients with lower grade obstruction may not present until later in childhood. Discovery of the lesion does not occur until adulthood in some patients, whereas others are asymptomatic throughout life.
Abdominal radiographs are normal in most patients with congenital antral or pyloric stenosis. If there is severe obstruction, the stomach is dilated (unless the child has recently vomited) and there is a paucity of bowel gas in the small intestine and colon. The most common appearance of an antral web on radiographic contrast studies is a thin, band-like structure that is oriented roughly perpendicular to the long axis of the lumen. In some instances, dilation of the antrum on both sides of the web results in a figure-of-eight or double bulb appearance. The orifice of the web can be central or eccentric. Manifestations of peptic ulcer disease are sometimes present. Sonographic examination demonstrates a congenital antral web as a linear echogenic structure in the lumen.10
Segmental antral stenosis results in a localized circular narrowing of the gastric antrum on contrast studies. The appearance is similar to that of the muscular constriction that occurs with peristalsis. However, the narrowing is persistent when viewed fluoroscopically. In fact, lack of distensibility of the involved area is sometimes the only radiographic finding.
A gastric duplication is a rare developmental mass that is nearly always cystic. The stomach is the least common site of GI duplication anomalies. The pathogenesis likely involves anomalous separation of the endoderm and notochord. Small intramural cysts may arise from persistent vacuoles within the primitive foregut epithelium. Gastric duplications are most often located along the greater curvature of the stomach; the antrum is the most common site. Occasionally, a tubular duplication is located adjacent to both the stomach and esophagus.
A gastric duplication is a developmental cyst that has a lining of intestinal epithelium. Gastric mucosa is frequently present; pancreatic epithelium is less common. Although usually quite small at birth, most gastric duplications progressively enlarge due to the accumulation of secretions. The most common presenting complaints are abdominal pain and vomiting, as the enlarging cyst compresses or obstructs adjacent structures. Ulceration related to the presence of gastric mucosa in the lesion can lead to hematemesis or melena.
Most gastric duplications do not communicate with the lumen of the stomach. Therefore, fluoroscopic contrast studies show a smooth, intramural, extraluminal mass. In rare instances, contrast passes into the lumen of the duplication via the stomach or esophagus. Sonography readily demonstrates the cystic nature of a gastric duplication. The contents of the cyst are anechoic in some patients, but elevated echogenicity can occur due to hemorrhage or inspissated secretions. It is often possible to demonstrate the “bowel wall signature” of the cyst wall with high-resolution sonography. The inner mucosal layer is a thin echogenic structure and the outer (muscular) layer is hypoechoic. The peripheral serosa is hyperechoic.
A contents of a gastric duplication typically have low attenuation on CT, low signal intensity on T1-weighted MR images, and high signal intensity on T2-weighted images. As with sonography, there is some variability between patients with regard to the characteristics of the cyst. Occasionally, there are calcifications in the wall of the lesion. Cross-sectional imaging studies readily demonstrate the origin of the cyst from the wall of the stomach if the lesion is small. The appearance of a larger gastric duplication cyst sometimes overlaps that of a pancreatic cyst, omental cyst, splenic cyst, or mesenteric cyst.
A gastric duplication cyst that contains gastric mucosa is often demonstrable with pertechnetate scintigraphy as an ectopic focus of radiopharmaceutical accumulation. However, the prominent normal uptake in the wall of the stomach can interfere with visualization of a small adjacent lesion.
Gastric diverticula can be congenital or acquired and true or false. A true congenital gastric diverticulum is a type of duplication anomaly that communicates with the stomach lumen. This type of diverticulum contains all layers of the stomach wall in normal proportions. A false diverticulum represents protrusion of mucosa and submucosa through an area of deficiency or absence of the muscular layer; this type of gastric diverticulum is quite rare in children.
Gastric diverticula, particularly false diverticula, are usually asymptomatic. A large antral diverticulum can cause symptoms (vomiting or abdominal pain) due to compression of the antropyloric region. Because a true gastric diverticulum contains gastric mucosa, it can become ulcerated and thereby produce hematemesis, melena, and abdominal pain.
Fluoroscopic contrast studies show a gastric diverticulum as a mushroom-shaped contrast collection along the wall of the stomach. Most often, the neck of the diverticulum is narrow and the apex is round. A broad-based shallow diverticulum can mimic the appearance of a gastric ulcer; however, tangential images show the diverticulum to project beyond the margin of the gastric wall. Most true gastric diverticula are located in the posteromedial wall of the stomach near the gastroesophageal junction. False diverticula tend to occur along the greater curvature and near the pylorus.
Microgastria refers to a congenitally underdeveloped stomach. This anomaly most often occurs as an isolated lesion, but sometimes is associated with intestinal malrotation or other anomalies of abdominal organs. Anomalous development of the pancreas (“primitive pancreas”) can occur in association with microgastria. Asplenia is another potential association; unlike most other forms of asplenia, congenital heart disease is often lacking in infants with microgastria.
The stomach in patients with microgastria has a tubular configuration, with lack of development of the greater and lesser curvatures. There is markedly diminished capacity. The lower esophageal sphincter is incompetent, resulting in severe gastroesophageal reflux. The lower esophagus sometimes serves as a secondary reservoir for ingested food. Fluoroscopic examination often shows slow emptying of the dilated inferior segment of the esophagus. In some patients, there is to-and-fro motion of material between the dilated esophagus and the small stomach. Compensatory dilation of the duodenal bulb can also occur (Figure 35-3). Most patients with microgastria develop feeding difficulties early in infancy, with vomiting and regurgitation. There is, however, a spectrum of severity with regard to the clinical manifestations and the degree of gastric underdevelopment.
Intrathoracic displacement of the stomach is common in infants with a large left-sided congenital diaphragmatic hernia. Other abdominal structures always accompany the stomach in this situation. Superior displacement of the stomach through a congenital hiatus hernia is a rare lesion; this is termed intrathoracic stomach. A congenitally short esophagus is occasionally associated with this anomaly. Intrathoracic stomachs are prone to volvulus (Figure 35-4).11–13
Heterotopic pancreas (ectopic pancreas; aberrant pancreas) refers to pancreatic tissue that lacks anatomic and vascular continuity with the normally-located pancreas. Despite the ectopic location, the heterotopic pancreatic tissue can have all the elements of normal pancreas, including acini, ducts, and islets of Langerhans. The prevalence in the general population is 1% to 2%. Heterotopic pancreas can occur in various locations, the most common of which are the stomach, duodenum, and appendix. Ectopic pancreatic epithelium can also be present within a Meckel diverticulum or gastric duplication. The most common location of gastric heterotopic pancreas is the greater curvature in the antral region. Ectopic pancreas is usually asymptomatic and is discovered as an incidental finding on a fluoroscopic contrast study of the upper GI tract or at endoscopy. Those patients who have symptoms usually suffer pain or manifestations of GI tract hemorrhage or obstruction.
The typical appearance of gastric heterotopic pancreas on a barium GI study is that of a smooth, 1 to 2 cm diameter mound of tissue that projects into the gastric lumen. There is often a central umbilication or niche that represents the orifice of a rudimentary duct. When present, this finding is pathognomonic for heterotopic pancreas. With sonography, gastric ectopic pancreas appears as a focus of broad-based or nodular gastric wall thickening that projects into the lumen. The central umbilication is sometimes visible on high-resolution sonography. CT or MR evaluation typically demonstrates a submucosal location of the mass. CT gastrography allows noninvasive depiction of the surface anatomy.14
Infantile hypertrophic pyloric stenosis is an acquired idiopathic thickening of the antropyloric portion of the stomach that results in gastric outlet obstruction. This abnormality occurs with a frequency of approximately 2 to 4 children per 1000 births in the United States. The prevalence varies somewhat between regions of the world.15 Infantile hypertrophic pyloric stenosis is the most common condition to require surgery in infants. There is a greater prevalence of pyloric stenosis in males (>80% of cases in the United States) and whites. Epidemiological factors that are associated with a lower prevalence include high birth order, older maternal age, higher maternal education, and low birthweight. Approximately 30% of patients with pyloric stenosis are firstborn children. There is a positive family history in approximately 5% of cases. Approximately 7% of children with infantile hypertrophic pyloric stenosis have a major developmental anomaly; the most common concomitant malformations are intestinal malrotation, urinary tract obstruction, and esophageal atresia.15
The major pathological characteristic of infantile hypertrophic pyloric stenosis is thickening of the muscular layer of the antropyloric portion of the stomach. Hypertrophy predominantly involves the circular muscle of the pyloric and prepyloric areas; the longitudinal muscle is largely unaffected. The mucosa in this area is also thickened and edematous. The pathogenesis of hypertrophic pyloric stenosis is multifactorial, involving a combination of genetic and environmental factors. In nearly all instances, the pylorus of affected infants is normal at birth, muscular hypertrophy develops early during infancy, and progression to symptomatic disease occurs over a course of days to weeks. Hypergastrinemia, gastric hyperacidity, and increased pyloric vascularity may be predisposing factors in some patients. There is evidence of an association between hypertrophic pyloric stenosis and the administration of erythromycin, with the greatest risk in infants who receive the medication within the first 2 weeks of life. There is also evidence of an association with exposure to macrolide antibiotics via breast milk.
Hypertrophic pyloric stenosis typically presents with excessive vomiting in a young infant. The mean age at presentation is approximately 4 weeks. The peak age range at presentation is between 3 and 6 weeks. Presentation during the newborn period and after 3 months of age is rare. The vomiting is usually mild initially, resembling the spitting up that occurs with gastroesophageal reflux. In most instances, there is rapid progression to projectile vomiting; this is reported in approximately 90% of infants with pyloric stenosis. Typically, the child demands to be refed soon afterwards (i.e., a “hungry vomiter”). The vomitus is nearly always nonbilious. In the absence of appropriate medical care, excessive vomiting in infants with hypertrophic pyloric stenosis can lead to dehydration and hypokalemic alkalosis. Jaundice is an occasional finding in these children, apparently due to diminished hepatic glucuronyl transferase activity or increased enterohepatic circulation of bilirubin.16
Physical examination of the infant with hypertrophic pyloric stenosis may demonstrate prominent peristaltic waves along the anterior abdominal wall in the region of the stomach. These waves typically progress from the left upper quadrant across the epigastrium. The hypertrophied pyloric muscle is sometimes palpable in the mid or right epigastrium as an olive-shaped mass. The olive is often best appreciated when the stomach is relatively empty, for example, after vomiting or tube decompression. In the appropriate clinical situation, the identification of a classic palpable pyloric mass is sufficient for initiation of surgical therapy.17
Standard abdominal radiographs often provide substantiating information for an infant with suspected hypertrophic pyloric stenosis, but the findings are not definitive. Potential radiographic findings include gastric distention (e.g., extension of the greater curvature below the level of the L2 or a gastric diameter of >7 cm), a prominent amount of air in the stomach, indentation of the gastric wall by peristaltic waves, a mottled or frothy appearance of the gastric contents, wall thickening of the gastric antrum, and a paucity of gas in the small intestine and colon (Figure 35-5). The presence or absence of distention of the stomach with air can be misleading, however. Crying and air swallowing can cause gastric distention in a normal infant. The infant with gastric outlet obstruction can have an empty stomach due to vomiting shortly prior to radiography. Forceful vomiting in children with a gastric outlet obstruction occasionally leads to pneumatosis of the gastric wall (Figure 35-6).18
The 2 main imaging techniques for the diagnosis of hypertrophic pyloric stenosis are sonography and upper GI contrast examination. Sonography offers the advantages of high diagnostic sensitivity, a lack of ionizing radiation, and the ability to image the pyloric muscle. However, sonography is dependent on the availability of an experienced operator and is poorly suited for the diagnosis of mimicking conditions. Radiographic contrast studies of the stomach establish the diagnosis of hypertrophic pyloric stenosis with very high sensitivity and specificity. This technique also provides accurate evaluation for other causes of vomiting, such as gastroesophageal reflux, congenital duodenal obstruction, peptic ulcer disease, and malrotation. Because gastric emptying is often quite delayed in children with hypertrophic pyloric stenosis, fluoroscopic time should be utilized judiciously to minimize radiation exposure; if there is complete lack of gastric emptying, sonography is a helpful confirmatory technique.
The 3 major radiographic signs of hypertrophic pyloric stenosis on upper GI tract contrast studies are delayed gastric emptying, narrowing and elongation of the pyloric channel, and mass effect from the enlarged pyloric muscle. Gastric emptying time, however, varies substantially between infants with pyloric stenosis; delayed gastric emptying alone is not sufficient for the diagnosis. Relatively prompt emptying into the duodenum occurs in some children with pyloric stenosis. Delayed gastric emptying can result from various conditions other than hypertrophic pyloric stenosis (see below). Generally, some degree of gastric emptying should occur within 10 minutes of ingestion of contrast in the normal infant.
Persistent elongation of the pylorus is universally present in children with hypertrophic pyloric stenosis. This most often has the appearance of a single, thin, long collection of contrast within the pyloric channel, that is, the “string sign.” The pylorus in these children nearly always has a curved configuration, with the convexity of the curve directed to the right, producing the “J sign” (Figure 35-7). In some patients, contrast within the pylorus is trapped between thickened folds of the pyloric mucosa such that 2 (or more) parallel streaks of contrast are present; this is termed the “double track sign” or “double string sign” (Figure 35-8). Transient apparent elongation of the pyloric channel is a common finding in normal infants and occurs in those with pathologic pylorospasm. Therefore, careful documentation of persistence of pyloric channel elongation is important for an accurate diagnosis of hypertrophic pyloric stenosis. It is essential that the pyloric channel be evaluated in a true tangential orientation such that the length is accurately characterized. Appropriate fluoroscopic visualization of the pyloric channel may be difficult if the stomach is distended; tube decompression should be performed when needed to assure diagnostic accuracy.19
Figure 35–7
Hypertrophic pyloric stenosis.
A steep oblique image shows elongation and narrowing of the pyloric channel, the string sign. There is a curved configuration of the pylorus, the J sign. There is a “beak” of contrast at the entrance of the pylorus. Impression on the antrum by the pyloric muscle produces the shoulder sign (arrow).
Mass effect due to enlargement of the pyloric muscle is an important confirmatory finding for the radiographic diagnosis of hypertrophic pyloric stenosis. Impression on the contrast-filled antrum by the thickened pyloric wall produces the “shoulder sign” (Figure 35-6). This is best visualized when the antrum is relaxed and somewhat distended with contrast. As a peristaltic wave approaches the thickened pyloric muscle, a small triangular or oval contrast collection may form at the junction between the pyloric tumor and the lesser curvature; this is termed the “tit sign” or “pyloric tit” (Figure 35-9). Accumulation of contrast at the entrance of the pyloric channel results in the “beak sign” (Figure 35-6). If there is adequate contrast within the antrum and the duodenal bulb to outline both margins of the thickened pyloric wall, an “apple core” appearance may result. The demonstration of 1 or more of these signs in isolation is not diagnostic of hypertrophic pyloric stenosis, as these appearances can occur transiently in normal infants and in those with pylorospasm.
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