Fig. 2.1
Plain abdominal radiographs: supine antero-posterior view (a) and trans-lateral view (b) show the presence of pneumoperitoneum
All cases of pneumoperitoneum, however determined, and upper-obstructive conditions have an exclusively radiographic diagnosis – duodenal atresia with a double-bubble sign; less frequently pyloric atresia, with a single-bubble sign; and jejunal atresia, with a few dilated loops causing upstream obstruction and complete absence of air downstream (Fig. 2.2). None of these conditions usually require further radiological evaluation after radiography: contrast studies are usually contraindicated, and additional procedures are not usually helpful and may even delay surgery, resulting in death.
Fig. 2.2
Plain abdominal radiographs: duodenal atresia with the double-bubble sign, due to distension of the stomach and proximal duodenum (a) and jejunal atresia (b), with a few dilated loops and absence of air in the lower portion of the abdomen. Note the presence of thoracic right-side hemivertebra (a)
The role of the plain abdominal radiograph combined with a chest radiograph in the diagnosis of esophageal atresia should be mentioned; this disease is suspected at prenatal US by the combination of polyhydramnios, reduced intraluminal liquid in the fetal gut, and inability to detect the fetal stomach.
Radiological confirmation of esophageal atresia is based on findings on AP and lateral chest radiographs, which show a blind pouch of the proximal esophagus, which is distended with air. Radiographic evaluation should always include the abdomen to assess the presence of gastrointestinal air due to the existence of the fistula, allowing the classification of tracheo-esophageal atresia. In types I and II there is a complete absence of air in the stomach and bowel, whereas in types III and IV, air is commonly present.
When an H-shaped fistula without atresia is suspected, an esophagogram with low-osmolality water-soluble non-ionic contrast media can show the fistula [6].
The plain abdominal radiograph also has a role in the early diagnostic phase of anorectal malformations; in such cases, you need to perform, with classification intent, a plain abdominal radiograph in the trans-lateral prone view for the evaluation of the rectal cul-de-sac and its distance from the perineum.
Furthermore, this study allows you to detect the sacrococcygeal anomalies that are often found in caudal regression syndrome or other skeletal abnormalities in a more syndromic context (VACTERL association; vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities).
2.1.2 Contrast Studies
Contrast studies remain as key to the demonstration of many diseases, both congenital and acquired. Their use, however, is slowly declining, thanks to the increased availability and dissemination of endoscopic techniques and video capsule endoscopy (VCE).
The aim of the modern radiologist is to work in close collaboration with the gastroenterologist and surgeon, to perform contrast studies only in selected patients, using the correct technique, at the lowest radiation dose possible to meet specific diagnostic questions.
Many diseases are also studied exclusively by a continuous fluoroscopy technique, by the last image-capture technique, or by pulsed fluoroscopy with capture of the acquired series. High-dose standard full exposures are reserved for cases of difficult diagnosis or when more definite anatomical detail is essential (e.g., in thin tracheo-esophageal fistulas).
2.1.2.1 Contrast Studies of the Upper Gastrointestinal Tract
Contrast studies of the upper gastrointestinal tract are upper gastrointestinal (UGI) series, small bowel follow through (SBFT), and small bowel enema.
Upper Gastrointestinal (UGI) Series
In well infants or children, barium is the preferred contrast medium for UGI series.
For imaging of the esophagus, stomach, and duodenum there is a choice of barium formulations and the choice of preparation is at the discretion of the radiologist.
As mucosal detail is rarely required, or indeed obtainable in children, preparations with a lower density are used; these can be successfully diluted, do not settle out and set while in suspension, and do not flocculate in the time taken to perform the test.
In neonates, especially premature infants, and in circumstances where aspiration is a risk or a perforation of the gastrointestinal tract is suspected, a low-osmolality water-soluble non-ionic contrast medium is ideally used (Fig. 2.3).
Fig. 2.3
Upper gastrointestinal series: gastroesophageal reflux with massive aspiration
The child should be starved for approximately 3–4 h before the study, or for the maximum gap between feeds if still breast-fed.
High-density high-osmolality water-soluble non-ionic contrast media should never be used because of the risk of aspiration and consequent possible serious complications, such as acute pulmonary edema [1, 3–5].
Although the 24-h pH probe is now the mainstay for making or confirming the diagnosis of reflux in children, UGI series are still used in many centers to confirm that the underlying gastrointestinal anatomy is normal. Conversely, the presence or absence of reflux during a routine UGI series should be noted, as this may be an important incidental finding.
Reflux often occurs immediately after the passage of the bolus (liquid or solid) through fractionally delayed closure of the gastro-esophageal junction (GEJ). Thus, if water is given (two or three consecutive mouthfuls are sufficient) even small amounts of reflux of barium at the GEJ may be captured. Beaking of the GEJ is a cardinal sign that reflux is likely to occur imminently, and if the radiologist sees this he/she should wait for a few more moments to see whether this is confirmed. If reflux does not occur after two or three episodes of drinking water then the child should be turned to the left lateral (LL) position and then slowly returned to supine. This encourages barium to wash over the GEJ, which may cause reflex relaxation of the GEJ with subsequent reflux. If after these two maneuvers reflux has not been demonstrated, then the study should be ended. There is no indication for tilting the child head down or for performing any other non-physiological reflux- or vomit-inducing maneuvers [3–5].
Although tube esophagram has traditionally been the gold standard examination for H-type tracheo-esophageal fistula, a contrast swallow (performed in the correct way) can be sufficient for making the diagnosis. However, a normal contrast swallow does not absolutely rule out the presence of a tracheo-esophageal fistula, and if high clinical concern remains, then a tube esophagram is still indicated.
The tube esophagram (as part of a UGI series) remains the test of choice in those children known to have a risk of aspiration or those being ventilated at the time of the study. UGI series may be performed for no other reason than to reveal an alternative explanation for the child’s symptoms, such as significant reflux.
It is worth noting that even a contrast swallow followed by a high-quality tube esophagram does not always demonstrate an occult fistula, and in occasional cases bronchoscopy may also have to be performed. Similarly, bronchoscopy may miss a fistula revealed by a contrast study. The tests are therefore complementary [6].
SBFT and Small Bowel Enema
Both SBFT and small bowel enema examinations are in precipitous, and probably terminal, decline with the advent of VCE, MRI of the bowel, and the use of US in examining the bowel.
The SBFT may still be performed in specific circumstances, including the following: in preparation for elective gut resection for surgical planning, when information regarding small bowel transit is required (such as in pseudo-obstruction and dysmotility states); in suspected subacute obstruction, or obstruction (noting that in adults CT is now routinely used for this indication, but this is not standard practice in pediatrics due to radiation dose concerns); in confirming patency in anticipation of VCE in patients at high risk of stricture (including patients with Crohn’s disease); in children who cannot tolerate VCE; and to assess complications of inflammatory bowel disease (IBD) if other modalities are not suitable.
The first part of the study is as for a UGI series, and the child can then sit outside the fluoroscopy room for another 20 min. The child should continue to slowly but steadily drink more contrast media during this time to ensure that there is a continuous column of contrast passing through the gut during the study. Serial images are then acquired at appropriate intervals to answer the clinical question [1–5].
2.1.2.2 Contrast Studies of the Lower Gastrointestinal Tract
Imaging of the lower gastrointestinal tract has not changed substantially over recent years, and a water-soluble contrast enema (for neonatal conditions) and, less frequently, a barium enema for older infants and children remain the mainstay of imaging [1–5, 7–11].
Loopograms have an important role in children who have a stoma. Low-density water-soluble contrast media is generally used, with the benefit that as more is instilled it does not become excessively dense and cause technical problems with exposure factors. However, there are a few instances, such as when trying to demonstrate a subtle fistula in an anorectal malformation, in which the limited use of denser water-soluble contrast media may be necessary to achieve sufficient definition. This will largely be at the discretion of the radiologist.
In neonates, enema studies are indicated in cases of bowel obstruction, especially lower intestinal obstruction.
Upper intestinal obstruction in neonates is characterized by bilious vomiting (which frequently occurs after the first feeding) and abdominal distension at clinical examination. Specific common causes of upper intestinal obstruction include atresia of the jejunum or proximal ileum and peritoneal bands. Partial obstruction can be caused by jejunal stenosis, peritoneal bands, duplication cyst, malrotation, and Meckel’s diverticulum.
The generic diagnosis of upper intestinal obstruction is usually straightforward at radiography, which demonstrates a few dilated bowel loops, more than would be seen in duodenal atresia and fewer than in ileal atresia or other causes of lower bowel obstruction. There is no gas in the lower portion of the abdomen in jejunal atresia. The patient usually requires no further radiological investigation, although barium enema examinations are still performed in attempts to exclude second and third areas of atresia lower in the bowel. In isolated proximal atresia of the jejunum, the colon is normal in size, because the remaining small bowel distal to the atresia produces sufficient intestinal secretions to produce a normal-caliber colon [1–5].
Lower intestinal obstruction is defined as an obstruction that occurs in the distal ileum or colon. Signs include large bowel obstruction with vomiting, abdominal distension, and failure to pass meconium. The differential diagnosis includes ileal and colonic atresia, meconium ileus or peritonitis, Hirschsprung disease, and functional immaturity of the colon. Anorectal malformations are also an important cause of lower intestinal obstruction, but are almost always evident at physical examination.
The diagnosis of lower intestinal obstruction is usually apparent at abdominal radiography because of the presence of many dilated intestinal loops, but radiographic differentiation between ileal and colonic obstruction is difficult, if not impossible. This distinction can readily be made with a barium enema study, which helps to determine the presence of microcolon (Fig. 2.4), indicates the position of the cecum with regard to possible malrotation, and shows the level of the obstruction in colonic atresia [1–4].
Fig. 2.4
Barium enema study shows severe functional microcolon
Ileal atresia is an important cause of lower intestinal obstruction. Plain radiographs (AP and LL views) show numerous dilated loops of bowel occupying the entire abdominal cavity and multiple air-fluid levels. When this degree of distension is reached, the mucosal pattern of the small bowel is effaced and it may be impossible to differentiate small bowel from colon. In such a case, a barium enema study is mandatory to determine the presence of a colonic lesion. In ileal atresia, the colon has a normal location but a minute caliber (functional microcolon).
Colonic atresia is less common than ileal atresia. It is often indistinguishable from obstruction of the distal ileum, especially when the atresia is located in the ascending colon. The colon proximal to the point of atresia is often massively dilated, and a mottled pattern of gas and feces may be identified. Barium enema examination usually reveals a distal microcolon with obstruction to the retrograde flow of barium at the site of the atresia [2–5, 8].
Meconium ileus is the result of intraluminal obstruction of the colon and lower small bowel, due to the impaction of meconium, and represents the earliest clinical manifestation of cystic fibrosis. Mechanical obstruction occurs when desiccated meconium pellets occlude the distal small bowel and the more proximal small bowel loops are distended with tenacious meconium paste. The abdomen is filled with gas-distended loops and occasionally there is a relative absence of air-fluid levels due to abnormally thick intraluminal meconium. The admixture of gas with meconium may give rise to a soap-bubble appearance similar to the fecal pattern in the colon in older patients.
Contrast enema examination will show a functional microcolon, involving the entire large bowel, and may show impacted meconium pellets, particularly in the right colon or in the distal ileum, caused by retained meconium (Fig. 2.5). Meconium ileus is among the few pediatric conditions for which an enema is used, with high-osmolality water-soluble iodinated contrast, because of its therapeutic effects. Advantage is taken of the high osmotic pressure of the contrast medium: the surrounding tissue is forced to release considerable amounts of fluid, which then flows into the gut and dissolves the inspissated meconium. Therefore, the enema is both diagnostic and therapeutic, and can be followed by the expulsion of meconium during or after the procedure.
Fig. 2.5
Contrast enema with high-osmolality water-soluble contrast in meconium ileus
Meconium ileus may be complicated by volvulus of a distal intestinal loop, perforation, atresia, or peritonitis [2–4, 8, 9, 12].
Meconium peritonitis is a chemical peritonitis resulting from intrauterine bowel perforation. Common underlying disorders include small bowel atresia, meconium ileus, volvulus, and intussusception, although some cases are idiopathic. The extruded bowel contents provoke an intense peritoneal inflammatory reaction, leading to the formation of dense fibrotic tissue. This tissue often calcifies, resulting in the characteristic intraperitoneal calcifications identified prior to birth with US and after birth with abdominal radiography and US. The calcifications of meconium peritonitis may extend into the scrotum through a patent vaginal process to produce a calcified mass in the scrotum [2–5, 8, 9, 12].
Hirschsprung disease is a form of lower intestinal obstruction caused by the absence of normal myenteric ganglion cells in a segment of the colon. The aganglionosis varies in length but always extends proximally from the anal canal, and the rectosigmoid area is involved in most cases. Ultrashort segment disease (in which aganglionosis is essentially limited to the region of the internal sphincter) is very rare, as is aganglionosis involving the entire alimentary tract. In children with Hirschsprung disease, the absence of ganglion cells results in the failure of the distal intestine to relax normally. Peristaltic waves do not pass through the aganglionic segment and there is no normal defecation, leading to functional obstruction. Abdominal distension, constipation, and bilious vomiting are the predominant signs and symptoms of obstruction and appear within a few days after birth.
Radiography performed in children with Hirschsprung disease yields findings similar to those in other forms of lower small bowel obstruction: variable gaseous distension of the colon and small bowel, often with air-fluid levels. The colon is usually difficult to identify accurately, and gas is usually absent in the rectum.
Barium enema studies demonstrate patency of the colon, which is short but usually normal in caliber. A transition zone between the narrow and dilated portions of the colon, in the shape of an inverted cone, is the most characteristic radiological finding. When this transition zone is observed, the examination should be discontinued, because filling of the more proximal dilated bowel beyond the transition zone may lead to impaction (Fig. 2.6). However, the distension of the bowel proximal to the segment of deficient innervation is gradual, and a transition zone is seen in only 50% of neonates with Hirschsprung disease during the first week of life. Abnormal contractions and irregular peristaltic activity of the aganglionic portion of the colon may be useful indicators of the disease, although they are nonspecific findings that are also seen in colitis.
Fig. 2.6
Hirschsprung disease. Plain abdominal radiograph (a) and barium enema (b, c). Note in c the ascent of the contrast to the stomach in the late study, due to complete aganglionosis
Twelve-hour-delayed postevacuation images are useful in dubious cases.
The radiological diagnosis of total colonic aganglionosis is difficult. Findings at barium enema examination may be normal or may include a short colon of normal caliber, microcolon, or a transition zone in the ileum [2–4, 10, 11].
Functional immaturity of the colon is a common cause of neonatal obstruction, particularly in premature neonates and in those whose mothers were treated during labor with magnesium preparations or sedatives; the condition also occurs in neonates with diabetic mothers. The condition has also been encountered in children with septicemia, hypothyroidism, or hypoglycemia. Functional immaturity of the colon comprises several entities, most notably small left colon syndrome and meconium plug syndrome. Affected patients have abdominal distension, difficulty in initiating evacuation, and sometimes vomiting; typically, however, the bowel distension is less severe than that seen with an organic obstruction. The condition is both diagnosed and treated with a contrast enema.
In small left colon syndrome, barium enema examination demonstrates a distended right and transverse colon with a transition to a very small-diameter descending and rectosigmoid colon near the splenic flexure. The rectum is usually quite distensible.
In meconium plug syndrome, barium enema examination with high-osmolality water-soluble contrast shows a small caliber of the left colon with a large meconium plug. The rectum is usually normal in size, unlike findings in Hirschsprung disease. The enema can be both diagnostic and therapeutic and is usually accompanied by the passage of meconium during or after the procedure [10, 11].
Typically, there is clinical improvement following the enema, and over the course of hours to days the radiographic and clinical signs of obstruction subside.
In older children the main indication for a barium enema is intestinal intussusception, with the enema used exclusively for therapeutic purposes, since the diagnosis is made by sonography.
The role of the enema in reducing intestinal intussusception is well known and recognized, but in the literature there are many differing reports about the contrast medium to be used; namely, air or liquid. An air enema is considered to be better at reduction, cleaner (appearance of peritoneal cavity at surgery when perforation occurs), safer, and faster, with less radiation when compared with a liquid enema. Reported perforation rates are not significantly different. The recurrence rates for air versus liquid enema reductions do not differ (approximately 10%). However, while the air enema may be preferred in experienced hands, the liquid enema is also safe and effective. Barium is no longer the liquid contrast medium of choice, due to the risk of barium peritonitis, infection, and adhesions when perforation occurs during the enema procedure. Neither sedation nor medications increase the enema success rate. More recent reports of air enema intussusception reduction show better results than liquid enema intussusception reduction. The air enema may use higher intraluminal pressure, which results in a higher reduction rate.
To avoid ionizing radiation exposure to children, the use of US with either water or air reduction techniques has been reported, showing intussusception reduction rates equivalent to those using fluoroscopy.
The use of delayed attempts (reports vary between 30 min and 1 day) after the initial attempt have shown further success in enema reductions of intussusceptions. Delayed enema should not be performed if the child is clinically unstable or if the initial enema does not partially reduce the intussusception.
The most important potential complication of enema use is bowel perforation (the mean perforation rate was 0.8%). There are no statistically significant differences between air and liquid enema perforation rates. This risk depends on each radiologist’s patient population and technique, as well as on the duration of symptoms. Because of this small but real risk of barium peritonitis, infection, and adhesions when perforation occurs during the enema procedure, iodinated contrast is preferred over barium when using liquid enema reduction.
2.1.3 Ultrasound (US)
Ultrasound (US) is an excellent imaging modality for the evaluation of the gastrointestinal tract in pediatric patients, so that it is now considered as an extension of the clinical evaluation, both in emergency conditions and for elective studies [13, 14].
In addition to the well established primary role of US in specific diseases, such as in hypertrophic pyloric stenosis and intestinal intussusception, the diagnostic reliability of US has been widely demonstrated in many other pathological conditions, such as in acute appendicitis, chronic intestinal inflammatory diseases (IBD), necrotizing enterocolitis (NEC), gastro-esophageal reflux, neonatal intestinal obstruction, intestinal malrotation, and acute volvulus in intestinal malrotation. Furthermore, US is successfully used even in less conventional applications, such as in esophageal atresia and anorectal malformations.
The well known advantages of US, particularly its lack of ionizing radiation and easy access, makes this imaging technique an ideal one for the evaluation of the pediatric patient with gastrointestinal tract diseases. Major drawbacks include its operator-dependency and reproducibility, apart from factors related to the patient, such as non-collaboration, obesity, and the interposition of a large amount of gas. Most of these limitations can be overcome with a comprehensive, careful, and dedicated examination technique using modern US capabilities.
US is also an excellent bedside high-yield imaging tool in intensive care units and it can also be used to guide therapeutic maneuvers, such as in the reduction of intussusception or in enema for meconium ileus.
In the past few decades, advances in US technology have greatly improved the quality of gastrointestinal US imaging, with a consequent positive impact on its diagnostic yield. Improvements in US probes, particularly high-resolution linear probes, permit better spatial resolution and better penetration in the far field, whereas improvements in contrast resolution can now be achieved with recent US modes such as image compounding, speckle/noise reduction filters, and (tissue) harmonic imaging.
Likewise, progress in Doppler techniques allows better depiction and quantification of even the slow flow of small vessels within normal and pathological gastrointestinal structures.
For any US examination the choice of adequate transducers, adjustment of basic parameters, and the choice of US modality is fundamental to obtain a proper image quality.
In general, the optimal transducer must have the highest possible frequency that is still able to penetrate the anatomical area of interest, providing the best spatial resolution.
The initial evaluation of the entire abdominal cavity is performed with a curved array transducer; then the individual structures of the gastrointestinal tract are specifically examined with a high-resolution linear probe, which allows detailed visualization of the esophageal wall, gastric wall, and bowel wall, as well as detailed visualization of the relevant surrounding structures. Not infrequently, curved array probes may also be needed in order to obtain a better access window to image deeper structures in older children (e.g., the esophago-gastric junction, the sigmoid colon, and the rectum) or to allow for a broader field of view.
In addition to the conventional trans-abdominal approach, other less common types of approaches might be necessary, and should be included in specific disease conditions, such as the suprasternal and mediastinal US approach to visualize the upper esophagus in tracheo-esophageal atresia or the perineal US approach to evaluate the anal canal or the distal rectal pouch location and its distance to the skin surface in anorectal or in cloacal malformations.
A well known limitation of US examinations is bowel gas interposition, but with a careful and proper bowel US technique this obstacle can often be partially overcome. Gentle graded compression is the essential technique in US of the gastrointestinal tract, as it displaces undesirable gas, shortens the distance to the skin surface, and isolates the bowel loops, while displacing adjacent ones. Furthermore, it helps to localize the origin of pain (“sonopalpation”) and to assess the bowel compressibility.
In small patients and particularly in critically ill neonates, SBFT can be performed and followed by US.
Filling techniques are the basis for therapeutic maneuvers under US guidance, such as in the nonsurgical reduction of an ileo-colic intussusception or in the attempt to resolve meconium ileus.
2.1.3.1 Upper Gastrointestinal Tract US
In neonates esophageal atresia is usually diagnosed with frontal and lateral radiograms, but US can provide additional precious information to the surgeon. Besides the role of abdominal and cardiac US in searching for associated abnormalities, mediastinal US allows the characterization of the length, morphology, and structure of the wall in a blind upper esophageal pouch; this condition can be improved by the administration of a small amount of saline fluid through the esophageal tube. Rarely, even a tracheo-esophageal fistula may be recognized by US [13].
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