**11. Inflammatory and infectious bowel diseases**

Inflammatory bowel disease (IBD) is a general term that covers a series of acute and non-acute diseases which do not require surgical treatment, ranging from selflimiting focal disorders to the debilitating and/or chronic diseases [1]. Diagnosis can be challenging due to nonspecific or atypical clinical presentation with extra-intestinal manifestations. US is useful in the diagnosis of IBD, especially in children by assessing bowel wall, peristalsis and surrounding mesentery with highfrequency transducers. Moreover, color Doppler increases the diagnostic accuracy and estimates the disease activity by showing vascularity. Presence of extra-intestinal complications such as abscess, fistula can also be evaluated with US.

While evaluating IBD, the thickening of the bowel wall can be divided into two categories according to US appearance [1]. 'Layered thickening' is shown as hyperechoic and organized wall thickening corresponds to mucosal inflammation with indirect involvement of submucosa. Whereas 'non-layered thickening' characterized by the loss of normal structure seen as a diffuse hypoechoic thickening without any reflective echoes. Based on the thickening type and localization, possible diagnoses are presented in **Table 2**.

Crohn disease is the most common IBD that requires frequent imaging because of its extensive involvement of GI tract, and phases of exacerbations and remissions [1, 6]. It is characterized as a chronic transmural inflammation of an unknown cause and can affect any part of GI tract. In 20% of cases, the disease first becomes symptomatic during childhood [39]. Although, the role in the diagnostic algorithm is emerging, bowel US in its current form cannot replace with CT or MRI but can provide complementary information in the evaluation of disease. The diagnostic performance of US for identifying lesions of Crohn disease has sensitivity of 75–94% and specificity of 67–100% [6]. The primary imaging features of Crohn disease are bowel wall thickening and loss of stratification. Affected segments are non-compressible, hypoperistaltic and have hypoechoic wall with a minimal thickness of >3 mm [6, 39]. The hallmark of active disease is increased vascularity of thickened bowel wall segments (> 5 mm) with 88% specificity and 95% positive predictive value [49]. Moreover, SMA flow volume is higher but resistive index is lower with active disease [6]. Remarkable extramural manifestations that can be seen on US include thickened, hyperechoic mesentery ('creeping fat' sign) and enlarged mesenteric lymph nodes (**Figure 4**). Strictures, fistula, phlegmon and abscess are common complications of Crohn disease that can be depicted on US but requires further evaluation with CT or MRI. On US strictures are identified in


**Table 2.**

*Sonographic pattern and location of common inflammatory bowel diseases.*

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

### **Figure 4.**

*An active Crohn's disease in an 11-year-old girl. Longitudinal (A) and transverse (B) section of inflamed bowel segments demonstrates layered wall thickening, increased echogenicity and prominent thickening of mesenteric fat tissue.*

70–79% of cases as a narrowed bowel segment accompanying dilatation and hyperperistalsis at the proximal part [6]. Fistulas are less common in children than adults, and US is not a reliable modality to depict fistulas with the sensitivity of 31–87% in different publications [50]. An abscess can be delineated with US as an irregular thick-walled aperistaltic fluid collection including internal echoes and sometimes air. The sensitivity of US for the diagnosis of abscessranges from 83–91% [51]. An abscess may mimic a bowel loop, but bowel segments are thin-walled and peristalsis of bowel can be seen on real-time imaging.

Henoch-Schönlein Purpura (HSP) is the most common pediatric vasculitis that frequently involve GI tract [3, 39]. The pathogenesis of the disease originated from the thrombosis of small vessels, which in turn can cause ischemia of the small bowel [39]. Bowel wall thickening and edema can be seen on US in 50–60% of cases [52]. Although typical skin lesions are the hallmark of the disease, bowel wall thickening in duodenum and proximal small bowel may occur before the appearance of skin lesions. However, HSP can affect any segment of the bowel. The most common US feature is diffuse circumferential bowel wall thickening (**Figure 5**). Focal intramural hemorrhage can be revealed as a hyperechoic lesion in the mucosa or submucosa. With intramural hematoma, bowel wall thickening may increase up to 9–10 mm and multiple skip lesions can be demonstrated [3]. In HSP patients with obstructive symptoms such as vomiting or hemorrhagic stool, one or more intussusception can be seen with intramural hematoma as a lead point [53]. In the active stage of the disease, hypervascularity on color Doppler imaging may present. Other less common vasculitides involving the bowel may also occur with a variable presentation but similar findings on US.

### **Figure 5.**

*An 8 year-old-girl with Henoch-Schönlein Purpura. (A) Ultrasound shows diffuse thickening of the intestinal wall (arrow). (B) Color Doppler demonstrates increased vascularity. Gray scale ultrasound from another part of abdomen (C) reveals hyperechoic mesenteric fat tissue (dashed arrows).*

Bacterial enterocolitis can occur by a wide variety of pathogens, including *E. Coli*, *Salmonella*, *Shigella* and *Campylobacter*. Common location is ileocecal region and US features are similar to other inflammatory disease, such as bowel wall thickening, increased echogenicity, reactive mesenteric lymph nodes, and mild intraabdominal free fluid. Viral gastroenteritis generally does not increase the thickness of the bowel wall; however enlarged lymph nodes and free fluid may be present [41]. *Tuberculosis* may also present with bowel wall thickening along with hepatosplenomegaly, omental thickening, and typical internal echoes and septations within ascites [54]. Parasites can be revealed by US as mobile, tubular hypoechoic structures with hyperechoic rim in *Ascariasis* infection, with parallel echogenic lines representing digestive system [41].

Neutropenic colitis, also known as typhilitis, is a necrotizing inflammatory process of cecum and terminal ileum usually seen in severe neutropenic and immunocompromised patients [39]. The typical US features are asymmetric, prominent wall thickening, with decreased echogenicity and loss of layering due to transmural inflammation. Echogenic foci can be seen in the bowel wall caused by circumscriptive hemorrhages or intramural air suggestive of anaerobic infection [55]. In thyphilitis, increased wall thickness may have correlation with a worse prognosis of the disease [41].

Pseudomembranous colitis is caused by the superinfection with *C. difficile*, often following a prior course of antibiotic treatment or rarely associated with shock, uremia, heavy metal intoxication or severe cardiovascular disease. The enterotoxin of *C. difficile* leads to severe inflammatory reaction within the colon between 1 and 6 weeks after the antibiotic treatment [24]. The common clinical findings are severe generalized abdominal pain, watery diarrhea, fever, and leukocytosis. The disease causes marked mucosal thickening of the colon, even thicker than other infectious colitis. On US, apart from thick hypoechoic mucosal layer, narrowing of the gut lumen and thickened hyperechoic submucosa can be demonstrated. In the majority of patients, the hypoechoic muscularis layer, which is outer than hyperechoic submucosa, appears normal and relatively thin. Intraabdominal free fluid is present in up to 77% of cases [24].

## **12. Mesenteric lymphadenitis**

Mesenteric lymphadenitis is a benign, self-limiting inflammatory condition that affects the mesenteric lymph nodes, more frequently pericecal ones. It may either occur as a primary inflammatory disease or may arise secondarily due to an abdominal disease. Clinically, this condition is commonly mistaken for appendicitis, since the symptoms are quite similar [22]. As the lymph node enlargement is the only finding on US, the diagnosis is made by excluding other possible etiologies of abdominal pain.

Various nomograms for normal ranges of mesenteric lymph node size have been reported and short axis of > 5 mm for lymph nodes are very common in healthy children [3]. Simanovsky et al. [56] suggested that, in the setting of normal appendix, cluster of > 3 lymph nodes with short axis of > 10 mm should be diagnosed as mesenteric lymphadenopathy. Enlarged lymph nodes are often oval and perinodal fat tissue may appear hyperechoic (**Figure 6**). A preserved fatty hilum is seen as a hyperechoic area at the center with vascular pedicle on color Doppler imaging. If the shape of enlarged lymph nodes is round rather than being oval, cortex is eccentrically thickened and there is loss of fatty hilum, neoplastic process should be suspected [3].

### **Figure 6.**

*Ultrasound (A,B) and color Doppler ultrasound (C) of the right lower quadrant of a 5-year-old girl diagnosed as mesenteric lymphadenitis. There are enlarged lymph nodes anterior to the iliac vessels. Color Doppler (C) demonstrates vascular supply from hilum of the lymph node.*
