**Abstract**

With recent technologies, ultrasound has become an extremely useful imaging modality for evaluating children with acute abdominal symptoms. Higher frequency transducers can be used in children than in adults, owing to their small body size, the presence of less fat tissue in the abdominal wall and peritoneal cavity leading to higher resolution than computed tomography in many circumstances without exposure to ionizing radiation. Real-time ultrasound imaging provides information about motion such as peristalsis, and newly developed harmonic imaging enables improved resolution with decreased artifacts. Beyond gray-scale ultrasound, color Doppler ultrasound provides information on vascularity which increases in inflammatory processes. Point-of-care examination includes ability to focus on the symptomatic area of the patient while performing real-time ultrasound imaging. Ultrasound is sufficient for the diagnosis of several gastrointestinal diseases that cause acute abdominal pain in pediatric patients helping to an accurate patient management in the emergency settings. Common gastrointestinal indications for abdominal ultrasound in children are hypertrophic pyloric stenosis, acute appendicitis, intussusception, inflammatory bowel disease, malrotation, midgut volvulus, hernia, and necrotizing enterocolitis. In this chapter, typical sonographic findings of aforementioned diseases, and possible differential diagnoses were discussed.

**Keywords:** Acute appendicitis, intussusception, inguinal hernia, necrotizing enterocolitis, hypertrophic pyloric stenosis, inflammatory bowel disease

## **1. Introduction**

Non-traumatic acute gastrointestinal (GI) disorders are common causes of presentation in the pediatric emergency department. Children have wide range of potential diagnosis, different from adults including congenital and acquired lesions. The causes of acute abdomen vary according to ages of the children. Since children are unable to give reliable history, have atypical presentations and accompanying extra-abdominal manifestations; evaluation and establishing the correct diagnosis is challenging.

Traditionally, pediatric abdominal ultrasound (US) examination focuses exclusively on parenchymal organs, putting less interest on the gastrointestinal tract [1]. However, recent US technologies and new transducers are able to perform a detailed examination with great contrast resolution of each section of the digestive system in pediatric age because of their smaller body size and less impaired by gas content and adipose tissues. The other well-known advantages of US, particularly its lack of ionizing radiation, easy access, low-cost and without need of patient

preparation, makes this imaging modality an ideal one for the evaluation of pediatric population in the emergency settings. Currently in many places, US is the first line of imaging over computed tomography (CT) and radiography for patients with acute abdominal pain. The main role of diagnostic imaging with US and color Doppler in the emergency is to determine whether the acute abdomen is due to a surgically or medically treatable disease, even though the exact pathology has not been diagnosed.

This chapter presents the basic aspects of US for evaluating the pediatric GI tract, including techniques, equipment, patient preparation and the anatomy. Then indications and sonographic findings of frequently encountered acute non-traumatic GI diseases in neonates, infants and children are highlighted with some exemplary cases. Acute traumatic GI tract injuries, oncologic emergencies, acute abdomen due to hepatobiliary or urogenital diseases are beyond the scope of this chapter.

### **2. Ultrasound technique and appropriate equipment**

New generation ultrasound equipment including the wide spectrum frequency probes provides high quality images of the gastrointestinal system, adjacent mesentery and related structures. Children's small body habitus and the presence of less fat tissue in the abdominal wall enable examination with high frequency transducers. Therefore US is increasingly used as the initial and follow-up study for investigating gastrointestinal tract pathologies in children and it is sufficient for the radiological diagnosis in majority of cases.

The contrast resolution of an US probe is dependent on the frequency, the velocity of sound in tissue and the number of cycles in the US pulse [2]. Depending on the age and size of the patient, a large convex-array (1–5 MHz) or smaller convex-array transducer (5–8 MHz) is a good option for beginning the examination for overview of the entire abdomen [3]. Following initial overview, a detailed analysis of the bowel wall and adjacent structures should be evaluated with a high frequency (10–18 MHz) linear-array transducer [1]. Tissue harmonic imaging is newly developed imaging software to increase resolution of the superficial parts of the field-of-view. It should be used to improve the delineation of bowel wall layers [2]. While evaluating anxious children in the acute setting, dynamic range should be lowered and the number of foci should be reduced to increase frame rate [4]. To demonstrate peristalsis, normal or abnormal motility, and motion of air bubbles in perforation or necrotizing enterocolitis; extended field-of-view can be helpful and cine clips should be recorded [5].

Doppler US evaluation is essential in GI system imaging, especially when looking at inflammatory diseases or neoplastic conditions. Doppler should be performed with a low wall filter and pulse repetition frequency should be adjusted as low as possible to prevent aliasing [6]. Power Doppler is a good method to overcome motion artifact in uncooperative children. As there are modern equipment and software, newer vascular imaging techniques, such as B-flow and superb microvascular imaging are brought into use by different vendors which are able to assess smaller vessels in the bowel wall [4].

US elastography is an emerging US technique to assess the stiffness of a tissue [5]. There are some studies in the literature regarding the usage of elastography for GI tract diseases, particularly in inflammatory conditions [7, 8]. The bowel is a hollow viscus with a lumen containing gas and fecal contents. The anatomy of the bowel is not ideal for US elastography as solid organs (e.g. liver or kidney). However, bowel wall thickening due to inflammation or tumor often reduces

### *Ultrasound of the Pediatric Gastrointestinal Emergencies DOI: http://dx.doi.org/10.5772/intechopen.99759*

motility and luminal contents that enable to perform US elastography more reliable [2]. Some studies suggest using US elastography in inflammatory bowel disease to differentiate inflammatory and fibrotic stenosis [9, 10].

Contrast enhanced US (CEUS) can be used to evaluate bowel wall vascularity and perfusion in real time [5]. It is performed after the intravenous injection of microbubbles that resonate and give rise to more intensely reflected signals [2]. Enhancement pattern, contrast quantification at peak intensity and dynamic contrast enhancement can be analyzed with CEUS [11, 12]. Enhancement pattern following bolus injection is used as a qualitative parameter. For example, patients with absent bowel wall enhancement can be separated from those with detected enhancement [2]. It can also be used in patients with complicated GI disorders when trying to differentiate a phlegmon from an abscess [13].

US examination of GI system must involve a systematic approach. While evaluating large bowel, the transducer is applied to the right iliac fossa to identify the cecum. Afterwards, colon can be followed through the ascending colon, transverse colon, descending colon, sigmoid colon and finally the rectum. Since the rectum is visualized behind the bladder, filled bladder is better to evaluate rectum and sigmoid colon. Longitudinal placement of the transducer is often better to identify the haustrations of colon segments [2]. The examination of the small intestine begins with the identification of ileocecal valve and the terminal ileum at the right iliac fossa. The examiner should identify the appendix, often inferior to the terminal ileum and follow the ileum as far as possible. Tracking the whole small bowel is generally not possible, therefore the abdomen should be scanned cranially and caudally parallel scans covering the whole abdominal area. The scanning approach may differ according to clinical scenario. For surgical disorders or trauma, a faster and a targeted approach are preferred, whereas for general and nonspecific complaints, more detailed examination can be performed.

Graded compression is a simple, essential and effective technique to push away gas filled bowel segments or intraabdominal fat [3, 4]. It decreases the distance between the transducer and target organ and enables to reach deeper with high frequency transducers. Although it was introduced for the diagnosis of acute appendicitis by Puylaert [14], now it has been performed for detection of bowel thickening and compressibility, and for specific diseases such as diverticulitis and colonic polyps [15, 16].

### **3. Patient preparation and clinical indications**

As a general principle, no preparation of the patient is required to perform gastrointestinal US, particularly in the emergency setting. However, to decrease the amount of food and gas in the gut, and to examine the gallbladder and biliary tree, a fasting period of 3 hours in newborn and 5 hours in children is recommended [1]. Physical activity also reduces the splanchnic flow, therefore patients should avoid from extensive activity before the examination [2]. Since the cold gel is one of the major complaints of children, gel warmer to warm the coupling gel can be used. If the infants or neonates are anxious and reluctant to be scanned; examiner can sit them on their mother's lap, get her lie down on the couch along with the child.

For stomach and pyloric examination, oral fluid intake or fluid ingestion via nasogastric tube is useful [4]. The distention of colon with anechoic fluid (water) ingestion, or with oral administration of hyperosmotic solutions allows the detailed examination of the haustration of colonic wall and adjacent structure [2]. The scanning of small intestine following the ingestion of iso-osmolar polyethylene glycol (PEG) solution is called US enterography or small intestine contrast US (SICUS).

Since the PEG solution is non-absorbable in the small bowel, retained fluid distends the intestine and induces the wall contractility. The PEG solution moves distally and distends whole loops of the entire small bowel. Following PEG ingestion, small bowel lumen diameter > 30 mm and wall thickness > 3 mm is abnormal [17].

Before beginning a US examination, examiner should be familiar with the abdominal symptoms, clinical presentations and laboratory findings of acute GI diseases. The most common presentations are pain, vomiting, diarrhea, fever, hematochezia and melena. Although some diseases have peculiar clinical findings, majority of cases have non-specific symptoms and clinical appearances [3]. US is generally suggested as the first line imaging modality in children with acute abdomen. Most common indications for gastrointestinal US in children are acute appendicitis, intussusception, hernia, hypertrophic pyloric stenosis, inflammatory bowel disease, and volvulus. Further indications involve necrotizing enterocolitis, duplication cysts, malrotation of the bowel [4]. Also US is widely performed for the disease of other intraabdominal structures such as mesenteric lymphadenitis, lymphoid hyperplasia of the appendix, infectious enterocolitis, omental infarct, epiploic appendagitis, specific inflammations such as tuberculosis, colitis with hemolytic uraemic syndrome and Henoch-Schönlein purpura [4]. The recent COVID-19 pandemic associated multisystem inflammatory syndrome in children (MIS-C) can also manifest with gastrointestinal system dysfunction which has been also a novel US indication since 2020 [18].

### **4. Challenges of GI ultrasound**

Major challenges of US is based on its operator-dependency and reproducibility [5]. The European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) suggests to set standards of training and education curriculum for GI system US to provide high quality performance in clinical practice [2]. According to EFSUMB recommendations; the operator should be able to recognize the normal anatomy of small intestine and large bowel initially. Following recognizing normal appearance of normal GI tract, the investigator should be able to perform a complete scanning of the gut; evaluation for focal or diffuse diseases, the presence of diverticular disease and its complications (perforation and obstruction), the peritoneal cavity, the mesentery, and the omentum for the inflammatory, infectious or malignant diseases [2].

There are other challenging factors related to the patient such as noncollaboration, obesity and interposition of large amount of gas [5]. Particularly retroperitoneal, paraaortic and retroduodenal areas are often danger zones that are not well delineated on US. If the graded compression technique is ineffective to eliminate gas interposition and US findings are unremarkable; intravenous contrast enhanced CT should be performed in patients with acute abdominal pain, especially if there is suspicion of gut perforation.

### **5. Normal anatomy**

While examining normal anatomy of GI structures; position, size, wall thickness and stratification should be evaluated. Many GI disorders appear as bowel wall thickening but normal bowel wall thickness may vary depending on peristalsis and the degree of distention [3]. Recent studies with high frequency transducers suggest that both normal small and large bowel wall thickness should be <2 mm when distended [19]. The exceptions are the pylor/duodenal bulbus and rectum wall which

*Ultrasound of the Pediatric Gastrointestinal Emergencies DOI: http://dx.doi.org/10.5772/intechopen.99759*

should be < 3 mm and < 4 mm respectively [20]. If the measurements were made from collapsed bowel wall, it should be reported since the wall of collapsed bowel is shown as thicker [2].

When examined with high frequency transducers, five sonographic layers of the bowel wall can be seen. When imaging the anterior wall (closer to transducer); the innermost echogenic layer is called as the mucosa-lumen interface which is not a part of actual GI wall. The second hypoechoic layer correspond to the deep mucosa, the third hyperechoic layer is submucosa which is most prominent in the colon [3]. The muscularis propria is the hypoechoic fourth layer which is most pronounced in the stomach. The outermost hyperechoic layer is the interface between muscularis and serosa. As the interface are hyperechoic and located distal to the real tissue, correspondence of histology and US layers are slightly different in the dorsal wall [2]. Therefore, evaluation of the layers should be made from the anterior bowel wall in diffuse inflammatory diseases. Bowel wall thickness measurement should be made perpendicular to the wall from innermost to the outermost echogenic layers [2].

The small intestine has three segments. The duodenum passes into the jejunum at the ligament of Treitz located in the left upper quadrant. The jejunum is often located in the left upper quadrant and usually collapsed with prominent folds, also known as valvula conniventes. They decrease and shorten from jejunum to ileum and best demonstrated at the fluid filled loops [2]. The ileum is located at the right lower quadrant and frequently involves fluid in normal patients. Sometimes cecum may be located intraperitoneal in variable positions even at the left lower quadrant of abdomen. The cecum and ileocecal valve is important landmarks to identify appendix which is usually below to the ileocecal valve. Although appendix is typically seen over the iliopsoas muscle medial to the cecum, lateral elevation or retrocecal course are not infrequent [2]. The normal appendix can be visualized in about 70% of healthy children with graded compression and it may increase depending on the experience of examiner and the resolution of transducer [21].

### **6. Acute appendicitis**

Acute appendicitis accounts for 80% of all abdominal surgical emergencies in pediatric population [22]. It is most frequently seen in second decade and is rare in children under two years of age, probably due to the funnel shape of appendix in infancy, which reduces the possibility of obstruction [23, 24]. Possible predisposing factors include lymphoid hyperplasia (due to past viral infection), dehydration, and low dietary intake of fiber [24]. Although the typical clinical presentation is acute onset of abdominal pain that may occur in the periumbilical area, radiating to the right lower quadrant, one-third of children have atypical clinical findings and symptoms, especially younger ones [23]. Other clinical signs are; fever, elevated acute phase reactants, nausea, vomiting and leg pain. Diarrhea is not present unless there is perforation and peritonitis, more frequently occurs in young children and confused with gastroenteritis [24]. Following clinical assessment and laboratory findings, imaging is the third component while evaluating the patients with suspected appendicitis. The routine US examination in suspected appendicitis reduces the negative appendectomies 50% and decreases the surgical complications and costs [25].

In patients with localized pain, transducer is applied to the point of maximum tenderness or pain. Self-localization facilitates the scanning, especially in patients with an aberrantly located appendix, and reduces the time of examination. If the patient cannot localize the pain or uncooperative; systematic evaluation starts in

transvers plane to identify ascending colon. Lowermost part of the ascending colon is the cecal pole and medial to the cecum ileocecal valve can be demonstrated. The most common origin of the appendix is 2–3 cm below to the ileocecal valve [26]. Pressure is gradually increased to displace gas and fecal materials in the cecal lumen to adduct appendix to the transducer. In obese children, a left oblique body position or an upward graded compression technique may be useful to displace the fat tissue of the abdominal wall [27]. Anatomical variations require a systematic approach to evaluate appendix and experience plays an important role in examination. There are several US features to distinguish between normal and inflamed appendix which are valid for both children and adults (**Table 1**) [25, 26, 28, 29].

The inflamed appendix is shown as a fluid-filled non-compressible distended aperistaltic tubular structure with a blind end (**Figure 1**). In the axial plane, it has a target appearance with thickened echogenic mucosal interface and hypoechoic muscular wall. Appearance of an appendicolith, which is an echogenic focus with a posterior acoustic shadowing, is supportive finding for the diagnosis (**Figure 1C**) [23]. However, intraluminal air is also echogenic and can mimic appendicolith (**Figure 1D**). A heterogeneous mass around appendix representing phlegmon, and a walled-off fluid collection representing abscess are often the signs of complicated appendicitis and perforation [23]. Complicated appendicitis can occur either as a gangrenous appendicitis (focal or diffuse necrosis of the wall) or as a perforation. There is continuous transition from phlegmonous uncomplicated to gangrenous appendicitis during the disease course. The most important indicator of gangrenous appendicitis is the loss of normal hyperechoic mucosa-lumen interface [30]. Other ancillary finding is the lack of vascularity on color Doppler. The rate of perforation following acute appendicitis is around 60% for a 3-year-old child, 50% for a 5-year-old child, and this incidence reduces with increasing age, because of limited ability to communicate and define complaints in little ones [31]. Moreover, small children are more prone to peritonitis and abscess formation, rather than phlegmon, following perforation due to underdeveloped omentum which confines purulent material [24].

Non-visualization of the appendix is an important problem while evaluating appendicitis. The major reason for false-negative scanning is inexperience examiner in GI US. Other challenging situations are retrocecal or pelvic position of appendix, thick abdominal fat tissue in very obese patients, or focal appendicitis confined to distal tip that account for 5% of cases [25]. Thus, the entire appendix should be delineated clearly [32]. In perforated appendicitis, an abscess may be misinterpreted as a gas-containing bowel loop. In these cases, indirect signs of appendicitis should be scrutinized around cecum [33].


### **Table 1.**

*Primary and secondary sonographic features of acute appendicitis.*

*Ultrasound of the Pediatric Gastrointestinal Emergencies DOI: http://dx.doi.org/10.5772/intechopen.99759*

### **Figure 1.**

*Three different cases with acute appendicitis. Ultrasound images of an 8-year-old boy demonstrate longitudinal (A) and transverse (B) section of inflamed appendix (arrow) with a diameter of 8.7 mm, and hyperechoic inflamed periappendiceal fat tissue. Ultrasound image of a 9-year-old boy (C) shows appendicolith (dashed arrow) within the appendix lumen, fluid level (asterisk) and dilatation distal to the obstruction. Ultrasound image of a 5-year-old girl (D) demonstrates inflamed appendix with a diameter of 8.6 mm and periappendiceal reactive fluid. Despite the inflammation, lumen is filled with air seen as echogenicity with dirty posterior shadow (thin arrows).*

Recent publications confirm the mild forms of appendicitis which is spontaneously resolved under antibiotic therapy without need for surgery [34]. Unfortunately, there are not any reliable criteria to differentiate mild courses on US that probably not require surgery [25]. Other pitfalls that lead to a false-positive diagnosis of acute appendicitis are; incorrect identification of the terminal ileum as inflamed appendix, Meckel's diverticulitis, cecal diverticulitis, dilated Fallopian tube or gonadal vein thrombosis [25]. Contrarily, appendiceal thickening can occur by other conditions such as Crohn's disease, infectious enterocolitis, peritonitis, ascites and appendiceal tumors such as mucocele, cystadenoma or carcinoid [25].

Over the last decades, the sensitivity of US for the diagnosis of appendicitis has reached to 95%, with specificity above 90% [23, 35, 36]. The accuracy of US is currently equivalent to CT and magnetic resonance imaging (MRI), even more accurate particularly in small children with less intraabdominal fat tissue. Pointof-care ultrasonography (POCUS) is increasingly done by emergency physicians for the diagnosis of appendicitis, but US is a highly operator dependent tool that requires experience and sufficient equipment. Consequently, adequate equipment, structured training program and quality control should be provided before clinical application. Consistent preoperative use of US for right lower quadrant pain can decrease the additional CT/MRI examinations to a low fraction [35, 37]. When initial US is inconclusive, second US following an observation period, or an additional MRI or CT examination can be considered. In children, MRI should be performed if possible to support the ALARA (radiation as low as reasonably achievable) principle. Some guidelines recommend several scoring systems for US to diagnose acute appendicitis [38]. Since these scoring systems roughly estimate the likelihood and do not prove appendicitis, they are not obligatory to use in routine practice [25].
