**Abstract**

The small intestine is a challenging organ for clinical and radiological evaluation. The introduction of radiological imaging techniques, which do not significantly disturb patients' comfort and safety, attempts to obtain an adequate diagnosis and valuable information. The aim is to determine the capabilities and potential of ultrasound, computed tomography (CT), diffusion-weighted imaging (DWI), and contrast-enhanced magnetic resonance (MR) enterography to establish the diagnosis and to evaluate the severity and activity of intestinal inflammation. Conventional ultrasound is a suitable orientation method in the initial evaluation of patients with Crohn's disease. At the same time, contrast-enhanced MR enterography provides an excellent assessment of disease activity, as well as the complications that accompany it. Contrast-enhanced MR enterography, combined with DWI, allows for excellent evaluation of disease activity and problems or difficulties following it. The examination can be repeated, controlled and can monitor patients with this disease.

**Keywords:** ultrasound, computed tomography, diffusion, inflammatory bowel disease, magnetic resonance imaging

### **1. Introduction**

Crohn's disease or enteritis regionalis is a chronic inflammatory disease of the digestive tract, predominantly of the small intestine. It is the most common small bowel disease in the United States and Europe: (3.1–14.6/100,000 in the United States and 0.7–9.8/100,000 in Europe, respectively) [1]. It occurs more frequently in the White population than in African-American and Asian ones, and is particularly common in certain ethnic groups [2]. The disease is equally present in both sexes and most often occurs between twenty and forty years of age [3].

Research into the epidemiology of IBD in areas with a sharply increased incidence may discover important etiological factors associated with the disease development [4].

Although the process most commonly affects the terminal ileum (60–80% of cases), the disease can occur in any part of the digestive tract, from the mouth to the anus [5].

Crohn's disease is a disease of segmental nature, in which healthy parts of the intestine are located between the affected ones. The inflammatory process spreads to all layers of the wall and affects the mesentery and local lymph glands [5, 6].

Many patients have lesions on the terminal ileum and the colon; in many cases, it is challenging to distinguish Crohn's disease from ulcerative colitis by differential diagnosis. Therefore, for ulcerative colitis and Crohn's disease, there is a common name - inflammatory bowel disease (IBD) [6, 7].

Inflammatory changes in the early stage of the disease are more pronounced in the submucosa than in the mucosa due to lymphedema [8]. The mucosa's lamina propria is infiltrated by polymorphonuclear leukocytes, forming crypt abscesses as a sign of the earliest lesion; this is followed by an enlargement of the lymphoid follicles surrounded by a red ring. Aphthoid ulceration appears on the mucosa, which progresses to deep, most often longitudinal ulcers in the disease's further course. As the disease progresses, the inflammation spreads transmurally with the formation of deep fissures and ulcerations along with the entire wall thickness.

In the advanced stage of the disease, fibrous strictures and extramural fistulas and abscesses develop [9].

Complications in Crohn's disease are common and can be local and extraintestinal [10].

### **2. Diagnosis of the disease**

Inflammatory bowel diseases, especially small bowel diseases, have always posed a diagnostic challenge [11]. The small intestine is a very challenging organ for clinical and radiological evaluation. Detecting the disease and determining its prevalence are two important clinical and diagnostic tasks.

In addition to the above, an important question to be answered is the degree of the disease's inflammatory activity. Although the medical issue was defined in the last century, diagnostic problems are still present. Advances in technology and the introduction of new diagnostic procedures promise better results.

#### **2.1 Imaging techniques in the diagnosis of Crohn's disease**

Ultrasound, computed tomography, and MRI are the techniques often used in the diagnosis of abdominal disease.

#### *2.1.1 Ultrasound*

Ultrasound is a widely used diagnostic modality that, due to its availability, simplicity, absence of harmful effects, and low cost of the examination, is the first diagnostic method used to diagnose abdominal diseases [12].

Ultrasound is generally performed without the use of a contrast agent. Some studies indicate greater sensitivity after the administration of an ultrasound contrast agent [13].

Technological advances and the growing experience of radiologists make ultrasound an increasingly valuable modality in diagnosing diseases of the gastrointestinal tract. The gradual compression technique and high-resolution multifrequency linear probes enable the displaying of changes in the intestinal wall [14]. Ultrasound plays an essential role in diagnosing diseases of the digestive tract, such as inflammatory bowel disease, small bowel obstruction, appendicitis, intussusception, and hypertrophic pyloric stenosis in newborns [15]. Factors that limit ultrasound examination of the abdominal organs, especially assessment of the digestive tract, are pain, pronounced flatulence, low spatial resolution, inability to display the rectum, and the distal part of the sigmoid colon. Recent studies, which compare Ultrasound and MRI in assessing the enlargement and inflammatory activity of Crohn's disease, indicate that ultrasound can localize the affected intestinal segments to some extent and the complications that accompany them [16, 17].

**11**

**Figure 1.**

*Thickening of the terminal ileum wall.*

*Role of Imaging in Small Bowel Crohn's Disease DOI: http://dx.doi.org/10.5772/intechopen.96098*

2 mm, and the large intestine up to 3 mm.

used to expel air from the intestines.

*2.1.1.1 Examination technique and ultrasound findings*

frequency linear probes in the field of 5–10 MHz.

[21]. A longitudinal view shows the tubular structure.

ing to determine the affected segment's exact length [22].

reliably by other radiological methods [20].

Sonographic lines of the intestinal wall correspond more to the interfaces than the wall's real histological layers. The central, thickened layer corresponds to the lamina submucosa, while the outer and inner hypoechoic layers correspond to the lamina mucosa and lamina muscularis respectively [18]. The wall is usually stratified if the lamina mucosa, submucosa, and muscularis propria are visible as separate layers. Loss of stratification is the inability to distinguish these layers or

The stomach wall's standard thickness is up to 5 mm, the small intestine up to

After the conventional abdominal ultrasound with a convex probe within the range of 2–5 MHz, the gastrointestinal tract examination is continued with high-

When inspecting the intestinal vortices, the gradual compression technique is

Incompressibility and thickening are vital signs of a pathomorphological change of the wall. The intestine's pathomorphological altered segment is characterized by concentric wall thickening, absence or reduction of peristalsis, and lack of compressibility under pressure with an ultrasound probe [19] (**Figure 1**). A wall thickness above 3 mm can be considered a pathological finding [20]. The discovery of a "pseudo-kidney" or "target sign" is the thickened, relatively hypoechoic intestinal wall surrounding the hyperechoic lumen, which is not specific and can be caused by other pathological conditions (neoplasms, intussusception, wall hematomas, hypertrophic pyloric ischemia, appendicitis, diverticulitis, etc.)

Some authors report a high percentage of detection of thickened intestinal convolutions (up to 90%) by high-resolution ultrasound, making it more challeng-

Therefore, the determination of the affected segment's length is estimated more

An increasing number of authors emphasize the value of ultrasound in detecting and monitoring chronic inflammatory bowel disease, and in evaluating drug therapy

distinguish lamina mucosa from submucosa with visible muscularis.

#### *Role of Imaging in Small Bowel Crohn's Disease DOI: http://dx.doi.org/10.5772/intechopen.96098*

*Endoscopy in Small Bowel Diseases*

and abscesses develop [9].

**2. Diagnosis of the disease**

the diagnosis of abdominal disease.

*2.1.1 Ultrasound*

contrast agent [13].

extraintestinal [10].

name - inflammatory bowel disease (IBD) [6, 7].

diagnosis. Therefore, for ulcerative colitis and Crohn's disease, there is a common

Complications in Crohn's disease are common and can be local and

Inflammatory bowel diseases, especially small bowel diseases, have always posed a diagnostic challenge [11]. The small intestine is a very challenging organ for clinical and radiological evaluation. Detecting the disease and determining its

In addition to the above, an important question to be answered is the degree of the disease's inflammatory activity. Although the medical issue was defined in the last century, diagnostic problems are still present. Advances in technology and the

Ultrasound, computed tomography, and MRI are the techniques often used in

Ultrasound is a widely used diagnostic modality that, due to its availability, simplicity, absence of harmful effects, and low cost of the examination, is the first

Ultrasound is generally performed without the use of a contrast agent. Some studies indicate greater sensitivity after the administration of an ultrasound

Technological advances and the growing experience of radiologists make ultrasound an increasingly valuable modality in diagnosing diseases of the gastrointestinal tract. The gradual compression technique and high-resolution multifrequency linear probes enable the displaying of changes in the intestinal wall [14]. Ultrasound plays an essential role in diagnosing diseases of the digestive tract, such as inflammatory bowel disease, small bowel obstruction, appendicitis, intussusception, and hypertrophic pyloric stenosis in newborns [15]. Factors that limit ultrasound examination of the abdominal organs, especially assessment of the digestive tract, are pain, pronounced flatulence, low spatial resolution, inability to display the rectum, and the distal part of the sigmoid colon. Recent studies, which compare Ultrasound and MRI in assessing the enlargement and inflammatory activity of Crohn's disease, indicate that ultrasound can localize the affected intestinal segments to some extent

prevalence are two important clinical and diagnostic tasks.

introduction of new diagnostic procedures promise better results.

**2.1 Imaging techniques in the diagnosis of Crohn's disease**

diagnostic method used to diagnose abdominal diseases [12].

and the complications that accompany them [16, 17].

Inflammatory changes in the early stage of the disease are more pronounced in the submucosa than in the mucosa due to lymphedema [8]. The mucosa's lamina propria is infiltrated by polymorphonuclear leukocytes, forming crypt abscesses as a sign of the earliest lesion; this is followed by an enlargement of the lymphoid follicles surrounded by a red ring. Aphthoid ulceration appears on the mucosa, which progresses to deep, most often longitudinal ulcers in the disease's further course. As the disease progresses, the inflammation spreads transmurally with the formation of deep fissures and ulcerations along with the entire wall thickness. In the advanced stage of the disease, fibrous strictures and extramural fistulas

**10**

Sonographic lines of the intestinal wall correspond more to the interfaces than the wall's real histological layers. The central, thickened layer corresponds to the lamina submucosa, while the outer and inner hypoechoic layers correspond to the lamina mucosa and lamina muscularis respectively [18]. The wall is usually stratified if the lamina mucosa, submucosa, and muscularis propria are visible as separate layers. Loss of stratification is the inability to distinguish these layers or distinguish lamina mucosa from submucosa with visible muscularis.

The stomach wall's standard thickness is up to 5 mm, the small intestine up to 2 mm, and the large intestine up to 3 mm.
