Thickness and stratification of the intestinal wall

Wall thickness must be measured perpendicularly through all layers, from the lumen/mucosa interface to the serosa. Normal values are up to 3 mm in the small intestine and 4 mm in the colon. The stomach can measure up to 6 mm, and the rectum up to 7 mm [14, 18, 19, 22]. While wall thickness is a quantifiable parameter and a primary pathological criterion in many studies, it is nonspecific, thickening being present in various inflammatory, infectious, ischemic, or neoplastic conditions [23]. Markedly asymmetric thickening is often observed in intestinal neoplasms and lymphomas [14, 24]. The intestinal wall consists of five layers, each with a distinct US pattern more discernible with slight parietal thickening rather than in physiological conditions (Figure 1) [25]. Though US layer definition does not precisely match anatomopathological classification due to the underlying physical principles of US imaging [26], but the loss of this stratification is a significant diagnostic feature [14].

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Figure 1. 

Normal ileal loop visualized in transverse scan with a high-frequency linear probe. The typical bowel stratification is clearly detectable. Starting from the inside, it is possible to clearly identify: the lumen (anechoic), the interface between the mucosa and submucosa (hyperechoic), the muscularis (hypoechoic), and the serosa (hyperechoic)

Caliper and intraluminal content

Caliper measurements within the normal range are up to 2–2.5 cm for small intestinal loops and up to 5 cm for the colon. Obstructive or paralytic processes result in increased caliper of intestinal loops [15]. Intraluminal content varies depending on the distance and type of meal ingested: Generally, there’s more fluid/particle-rich content in the small intestine, transitioning to a greater presence of gas artifacts in the colon (Figure 2) [15].

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Figure 2. 

Longitudinal scan of the ascending colon, visualized with a high-frequency linear probe (A) and with a convex probe (B). The characteristic haustra of the colon is clearly visible (arrowhead)

Peristalsis

US is unique in allowing the assessment of intestinal peristalsis, although operator dependency remains an issue. Hyperdynamic kinetics can be observed in conditions such as infectious colitis, malabsorption-related enteropathies, and the initial stages of mechanical ileus. However, in advanced diseases or paralytic ileus, peristaltic movements are reduced or absent [27].

Vascularization

Under physiological conditions, typically Doppler evaluation will not reveal any vascular signal in a nonticketed wall. Increased vascularization may be visible in case of wall thickening, suggesting an inflammatory or neoplastic condition. Conversely, the complete absence of blood flow raises suspicion of ischemic etiology [14]. In addition, contrast-enhanced US (CEUS), where available, could provide enhanced visualization of blood flow that traditional US might not capture. Currently available contrast agents, composed of gas microbubbles, upon their injection into the bloodstream enhance ultrasonographic imaging by providing superior visualization of tissue perfusion and microcirculation, offering a distinct contrast with adjacent tissues. Despite optimal adjustments, color Doppler fails to match the detailed assessment of tissue perfusion achievable with CEUS, as it does not allow for differentiation between non-vascularized structures and those with slow or minimal vascular flow. Moreover, US contrast agents boast a remarkable flexibility in administration, as they are suitable for use irrespective of organ function—this includes scenarios such as renal failure. They are also safe for children or pregnant women, and they have an excellent safety profile, with a low incidence of allergic reactions and adverse events. Preparing, administering the contrast agent, and interpreting CEUS results extend the examination by 5–20 minutes [28]. In specific cases, which will be discussed later in this article, CEUS represents a supplementary diagnostic resource [15, 23].

Surrounding structures

Several acute and chronic intestinal pathologies cause changes in the structures surrounding the affected loops, which are crucial for diagnosis. Inflammatory collections (abscesses or phlegmons), fluid accumulation, mesenteric hypertrophy, mesenteric lymphadenopathies, or pneumoperitoneum can be observed and are diagnostically significant [15, 21, 23, 27].

Acute abdomen

GIUS is recommended as the initial diagnostic method in patients presenting with an acute abdomen [1–3]. In expert hands, this technique has excellent diagnostic accuracy, providing a radiation-free complement to physical examination. It enables physicians to integrate clinical data, signs, symptoms, and images directly at the patient’s bedside [1] and has virtually infinite repeatability without any side effect, which is particularly valuable in cases involving women of reproductive age and children [13, 20]. Notably, when performed during the initial clinical evaluation, it can be a decisive diagnostic tool in patients with acute abdominal pain, helping to identify signs of acute appendicitis, acute diverticulitis, small bowel obstruction, and intestinal ischemia [2, 3].

Acute appendicitis

The EFSUMB guidelines advocate US as the preferred initial approach in all suspected cases of acute appendicitis (“Ultrasound first and always”), which is applicable to both adults and children [3, 5]. This strategy has demonstrated the ability to reduce unnecessary surgical interventions by 50% without compromising patient care [29]. In this context, US sensitivity, specificity, and accuracy have proven to be comparable, although slightly lower in most cases, to CT or MRI [30].

On the other hand, the American College of Radiology’s (ACR) Appropriateness Criteria provides guidance on the most suitable imaging techniques for diagnosing acute appendicitis, particularly in the context of right lower quadrant pain. According to these guidelines, abdominal and pelvic CT with intravenous contrast is typically the most appropriate initial imaging choice. US, however, may also be considered appropriate and is advised as the preferred imaging method in pregnant women, in conjunction with MRI of the abdomen and pelvis without intravenous contrast [31]. The difference between these approaches may be attributed to differences in patient characteristics and physical constitution, and partly to differences in health policy, a discussion of which is beyond the scope of this paper. Despite these differences, a point of care US, performed as a complement to clinical evaluation, can help to guide subsequent diagnostic pathways more precisely, facilitating an optimization of the use of radiological investigations without increasing costs. For instance, point-of-care ultrasonography is increasingly performed by emergency physicians to diagnose acute appendicitis but adequate equipment and training are mandatory [3]. Clearly, when US results are inconclusive or the diagnosis proves challenging—such as in cases involving obese patients, a retrocecal appendix, or focal inflammation—resorting to cross-sectional imaging is mandatory [3].

The objective of US examination is threefold: rule out alternative abdominal pathologies, confirm a typical presentation of appendicitis, or, conversely, exclude it when the appendix exhibits normal characteristics throughout its length. Additionally, US examination can raise the suspicion of complicated appendicitis (gangrenous or perforated), necessitating further diagnostic exploration and surgical assessment. Careful attention should be paid to the point of maximum tenderness, typically in the right iliac fossa. US findings for acute appendicitis include wall thickening > 3 mm in the longitudinal section, target sign appearance with anteroposterior diameter > 6 mm in the longitudinal section, non-compressibility, and tenderness upon gradual probe pressure (ultrasound McBurney’s sign). Abundant parietal vascular signals on color Doppler are indicative of acute inflammation, while peri-appendiceal fluid accumulation, mesenteric hypertrophy, and mesenteric lymphadenopathy are also relevant markers (Figure 3) [3, 21].

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Figure 3. 

Inflamed appendix. (A) Longitudinal view of an inflamed appendix, characterized by a noticeable thickening of both the appendix wall and its caliper. Additionally, there is a marked hyperechoic thickening of the surrounding mesentery. (B) Transverse ultrasound view further demonstrates the inflamed appendix, consistently highlighting thickening of the wall and mesentery across different scanning planes. (C) This image, corresponding to the transverse view in panel B, distinctly shows enhanced vascularization in the mesentery at microvascular imaging, indicative of a typical inflammatory response in appendiceal inflammation

The diagnosis of acute appendicitis is made easier in clinical practice when multiple US signs are present, specifically the observation of a thick-walled appendix with hyperechoic peri-appendiceal tissue in the area of greatest pain. Conversely, mesenteric lymphadenopathy, modest fluid accumulation, and mesentery thickening are nonspecific signs observed also in several other conditions [32].

Acute diverticulitis

GIUS has high diagnostic accuracy, with sensitivity and positive predictive values of approximately 90%. It often visualizes diverticula even in the absence of inflammation, helping clinicians in risk stratification and identify complications such as abscesses, phlegmons, perforations, or strictures. However, CT remains the gold standard for managing acute diverticulitis and its complications, particularly in obese patients and distal sigmoid diverticula [32]. In several European countries, a “step-up” diagnostic approach has been proposed, where GIUS serves as the primary tool followed by CT in cases of inconclusive or challenging US results, complex localizations, and complicated diverticulitis where CT offers superior delineation beneficial for potential surgical intervention [3, 32–35].

Diverticula can be visualized even in the absence of inflammation as protrusions of the wall containing echogenic material (air, feces, or fecaliths) with a posterior acoustic shadow (Figure 4A) [36, 37]. Diagnostic US criteria for acute diverticulitis encompass segmental wall thickening (> 5 mm) of a short intestinal segment with loss of compressibility, presence of an inflamed diverticulum in the thickened area (with varying echogenic appearances: hypo- or hyperechoic, with or without air artifacts in the lumen), and peri-loop mesenteric hyper-echogenicity due to inflammation (Figure 4B) [3, 21, 38]. Moreover, US can visualize potential complications such as abscesses, fistulas, free air, or abdominal fluid accumulation [36]. Grayscale US frequently struggles to differentiate between phlegmons and abscesses, as both conditions can manifest as heterogeneous hypoechoic masses. This similarity in visual presentation on US complicates the diagnosis, especially when no vascular signals are detectable on color Doppler. In such cases, phlegmons, which are typically managed conservatively, show diffuse enhancement on CEUS, while collections of pus remain completely avascular and are delineable after contrast administration. This is particularly important because abscesses, depending on their dimensions, often require intervention through percutaneous or surgical drainage to effectively manage the condition. Moreover, US and CEUS are pivotal in-patient follow-ups, enabling serial, non-invasive imaging with dynamic monitoring and timely adjustments of treatment strategies (Figure 5) [21, 39].

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Figure 4. 

Diverticula. (A) Non-complicated diverticulum on the sigmoid colon. This image shows a small, air-filled sac (diverticulum, between calipers) protruding from the wall of the sigmoid colon in the mesentery. The walls of the diverticulum and the adjacent bowel wall are not thickened, and the entire adjacent mesentery is also not thickened. (B) This image shows a diverticulum with markedly thickened and hypoechoic walls (arrowhead). A diverticulum, filled with air, also is visible (arrow). The adjacent bowel walls are thickened and hypoechoic (between calipers), while the mesentery is thickened and hyperechoic. These are clear signs of acute inflammation

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Figure 5. 

Complicated diverticulitis. (A) The sigmoid colon (longitudinal scan) has thickened walls (between calipers) and a diverticular outpouching (arrow). The mesentery is hyperechoic and thickened and a hypoechoic inflamed area surrounds the diverticula (arrowhead). (B) On CEUS the hypoechoic area within the mesentery appears completely avascular, confirming the presence of a small peridiverticular abscess

Small bowel obstruction

Small bowel obstruction is a common cause of acute abdomen and is characterized by varied and nonspecific clinical manifestations such as vomiting, acute pain, and abdominal distension. Early evaluation is imperative, and GIUS helps to confirm or rule out intestinal obstruction, offering insights into its location and potential causes, including adhesions, Crohn’s disease, tumors, hernias, and volvulus [40]. Moreover, GIUS assesses the risk of critical intestinal ischemia associated with obstruction, aiding in further diagnostic exploration and surgical assessment [1, 2].

In this context, the diagnostic accuracy of GIUS is comparable to, if not superior to CT. It exhibits greater sensitivity (91% vs. 87%) and specificity (96% vs. 81%), notably surpassing X-rays, which stand at approximately 75% sensitivity and 66% specificity [41]. However, CT remains the preferred diagnostic modality for assessing obstructive causes and complicated cases necessitating urgent surgical intervention, as well as for inconclusive US findings [2, 40]. Therefore, the EFSUMB guidelines advocate US as the primary approach in managing acute abdomen cases suspected of small intestinal obstruction, particularly in young patients and during pregnancy. Combining GIUS with CT remains suitable, as CT retains its diagnostic relevance in defining the obstruction location, organic causes, and severity [2].

US signs of uncomplicated intestinal obstruction include identification of dilated intestinal loops (> 2.5 cm) containing fluid and particulate material, along with altered peristalsis. It also provides a dynamic assessment of peristaltic movements, aiding the differentiation between dynamic and mechanical ileus. In dynamic ileus, physiological peristalsis diminishes or disappears, whereas mechanical ileus initially shows increased peristaltic movements that gradually decrease in the advanced stages. In the initial phases, thickening of the intestinal wall (> 3 mm) with hypertrophy of the valvulae conniventes (“keyboard sign”) may be visible, whereas over time, the wall tends to thin out and the valvulae to flatten (Figure 6). The site of obstruction can be determined by identifying the point at which dilated proximal loops transition to nondilated distal loops. This is particularly crucial for identifying specific pathologies causing obstruction, such as hernias, intussusceptions (Figure 7), neoplasms, or Crohn’s disease. Color Doppler imaging enables the assessment of parietal vascularization, allowing early identification of signs of ischemic distress [1, 2, 21].

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Figure 6. 

Intestinal obstruction. The image depicts a significantly distended small bowel loop, filled with fluid and having notably thin walls. The valvulae conniventes, (arrows), are flattened, indicating chronic obstruction. Fluid effusion (F), a sign of distress, surrounds intestinal loops

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Figure 7. 

Intussusception. (A) Longitudinal scan showing a segment of the intestine invaginated into itself. The characteristic ‘trident’ or ‘telescopic’ appearance of the bowel layers is evident, indicative of intussusception. (B) Transverse view of the same intestinal segment. The invaginated intestinal segment is visible, displaying the classic ‘target’ or ‘donut’ sign. This cross-sectional view provides further confirmation of intussusception, characterized by the concentric rings formed by the intussuscepted bowel

US signs indicating worsening obstruction include intraperitoneal fluid or free air, wall thickening > 4 mm, decreased or absent peristalsis in a previously hyperdynamic loop, and absence of wall vascularization on color Doppler [2, 42, 43].

Intestinal ischemia

For strongly suspected acute mesenteric artery ischemia cases presenting with abdominal pain, hemodynamic instability, and multi-organ insufficiency, a prompt angio CT is recommended as gold standard examination [44]. Yet, as the clinical presentation is often nonspecific, abdominal US and GIUS can serve as a preliminary panoramic investigation. This aids in guiding patients displaying US signs of ischemia toward immediate CT evaluation [2].

Distinct US patterns emerge based on the underlying etiology. In acute arterial ischemia asymmetric hypoechoic thickening of the intestinal wall, with reduced or absent peristalsis, may be visible. Furthermore, in this scenario CEUS is exceptionally sensitive in detecting reduced or absent parietal perfusion, a hallmark of ischemic segments, thus facilitating a prompt and accurate differential diagnosis from inflamed tracts, which typically exhibit increased vascularization often visible with color Doppler. CEUS is largely credited for its safety, with a low risk of adverse reactions. The US study during clinical assessment and a potential CEUS, which in expert hands extends the evaluation by 5–15 minutes may be crucial for preserving intestinal function and preventing further complications in ambiguous cases with a less suggestive clinical picture (Figure 8) [45, 46].

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Figure 8. 

Intestinal ischemia. (A) The descending colon is moderately distended with speckled content and thickened and hypoechoic walls. (B) On CEUS the walls appear completely avascular, indicating intestinal ischemia

In acute venous ischemia, a uniform hypoechoic and homogeneous thickening of the intestinal wall due to mucosal edema, along with reduced peristalsis, intraluminal secretions, and perienteric fluid accumulation can be observed [2].

In chronic arterial ischemia asymmetry between wall thickness can be observed but it’s usually less pronounced, as collateral circulation often compensates for perfusion [2, 47].

GIUS exhibits high positive predictive value (90%) in identifying ischemic colitis in elderly patients with sudden abdominal pain, diarrhea, or rectal bleeding. It demonstrates segmental thickening (extension > 10 cm) of the descending colon wall, showing no vascular signals on color Doppler [2, 48].

Intestinal perforation

When intestinal perforation is suspected, GIUS is recommended as a first line investigation, followed by CT in case of negative or inconclusive findings. This approach is justified by CT’s superior sensitivity in revealing pneumoperitoneum or pneumoretroperitoneum [49]. Clearly, the traditional radiological abdominal scan approach is losing significance, given its lower sensitivity (55–85% compared to 92% for US and 95% for CT) [50–52]. This approach does not offer any insights into the site and cause of perforation and fails to diagnose most other causes of acute abdomen [53].

While the presence of air poses a known challenge in performing US examinations, the focus should be on detecting gas collections and small air bubbles in upper positions, particularly between the anterior liver surface and the abdominal wall. These manifestations appear as hyperechoic lines or foci accompanied by reverberation artifacts. When free air obscures the left hepatic lobe and adjacent abdominal structures, a slight compression may displace the gas, revealing the liver in an alternating pattern [54]. Additionally, observing the movement of air artifacts in response to changes in patient position strongly suggests pneumoperitoneum [55].

Inflammatory bowel diseases

Crohn’s disease

In the realm of diagnosing inflammatory bowel diseases, colonoscopy remains the gold-standard examination due to its capacity for biopsies and histological diagnosis [56]. However, for assessing proximal extension and potential complications, recent consensus guidelines by the European Crohn’s and Colitis Organization (ECCO) and the European Society of Gastrointestinal Radiology (ESGAR) recommend GIUS, CT, or MRI as imaging techniques for identifying Crohn’s disease at its initial presentation, as well as for evaluating its location, activity, and potential complications with comparable diagnostic accuracy [6, 12]. Consequently, GIUS is endorsed as the primary choice for both the initial diagnostic phase and disease follow-up, primarily due to its favorable aspects of tolerance, safety, repeatability, and accessibility [57].

GIUS can reveal wall thickening with loss of stratification and reduced or absent peristalsis within the affected segments, thereby identifying the extent of the involved intestinal tract. Additionally, mesentery hypertrophy is often observed, appearing as hyperechoic with lymphadenopathies present, along with heightened vascularity evident in both the intestinal wall and mesentery, as seen on color Doppler imaging [3, 21]. When considering complications, strictures manifest as intestinal segments with thickened walls, accompanied by luminal narrowing and dilation of the upstream intestinal tract, often accompanied by accentuated peristalsis (Figure 9) [57, 58]. Fistulas appear as hypoechoic tracts, sometimes containing hyperechoic spots within, linking adjacent intestinal loops or an intestinal loop with other structures such as the bladder, muscles, or skin (Figure 10) [38, 58]. Wall abscess formations can be visualized as hypo-anechoic lesions, frequently displaying internal echoes due to air or debris presence, and thickened walls. The administration of contrast agents enables the differentiation between abscesses and phlegmons, as mentioned previously, and its virtually unlimited repeatability is extremely useful for short-term follow-up [21, 39, 46].

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Figure 9. 

Crohn’s disease. A short intestinal segment is shown with thickened walls (between calipers) and a significantly narrowed lumen. Upstream segment dilation with fluid content (F) is noted. The surrounding mesentery of the thickened loop is also thickened and hyperechoic (M)

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Figure 10. 

Enteric fistula (F) appears as a serpiginous, hypoechoic tract, delving into the thickened mesentery, establishing a pathological communication between the rectum (R) and the bladder (B). Notably, punctiform air artifacts (A) are observed inside the bladder adjacent to the anterior wall

Ulcerative colitis

Due to its primary impact on the mucosa and submucosal layers, endoscopy stands as the gold-standard examination for diagnosing ulcerative colitis [59]. However, GIUS has been proven to be an exceptional tool for non-invasive evaluation of disease extent, activity, and response to pharmacological interventions [4, 6, 60, 61].

Typically, moderate thickening of the intestinal wall (generally ranging between 4 and 9 mm) is observed, with preserved stratification in mild forms of the disease [62]. As ulcerative colitis advances to moderate and severe stages, stratification becomes less discernible and eventually disappears, causing the colon to appear contracted and linearized, thus losing its characteristic haustration (Figure 11) [4, 21, 61–63]. The intensity of wall vascularity observed in color Doppler imaging is directly correlated with clinical and endoscopic disease activity [64].

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Figure 11. 

Ulcerative colitis. The descending colon appears, contracted with thickened and hypoechoic walls (between calipers) hallmarks of inflammatory activity. While ultrasound effectively highlights these inflammatory changes, it is through endoscopic examination that a definitive diagnosis of ulcerative colitis is established

Given the increasing use of US as a primary diagnostic tool in acute conditions and/or for monitoring patients with inflammatory bowel disease, cases of toxic megacolon might be encountered. This condition is more likely to manifest as dilation of the transverse colon (often exceeding 6 cm), accompanied by thin, hypoechoic intestinal walls, and liquid or gaseous content [63].

Other gastrointestinal conditions

Malabsorption and celiac disease

A definite diagnosis of celiac disease with GIUS remains elusive. However, while individual US indicators of the disease lack specificity, taken collectively they support the diagnostic suspicion of intestinal malabsorption [65]. These indicators encompass fluid-filled dilation of loops, accentuated valvulae conniventes exhibiting a brain-like appearance, increased peristalsis, free peritoneal fluid, and inflammatory mesenteric lymphadenopathy (Figure 12). These US signs wane and vanish following adherence to a gluten-free diet, while their persistence could signal resistance to the dietary regimen [21].

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Figure 12. 

Malabsorption. In this depiction, the valvulae conniventes (C) are hypertrophic and are distinctly visible due to the presence of anechoic fluid content

Masses and neoplastic lesions

Although GIUS is not the primary method for detecting or staging intestinal neoplasms, it may guide further diagnostic exploration. Malignancies causing hypoechoic or heterogeneous, frequently asymmetrical, wall thickening leading to diminished lumen diameter with subsequent dilation of the upstream loops due to substantial stenosis can be observed (Figure 13). Polypoid formations protruding into the lumen may also be visible in some cases, typically appearing as hypoechoic nodules/masses. GIUS aids in identifying small-sized intestinal lesions that might otherwise elude endoscopic examination, thus guiding subsequent diagnostic and therapeutic approaches. Such lesions could include intestinal lymphomas, gastrointestinal stromal tumors (GISTs), neuroendocrine tumors, and, albeit rare, carcinomas (Figure 14) [65, 66].

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Figure 13. 

Intestinal lymphoma shows a typical asymmetric thickening of the walls of a small intestine loop. The posterior wall (between calipers) is significantly thicker than the anterior wall, and the intestinal lumen (arrow) is displaced in an eccentric position. The thickening begins and ends abruptly and appears markedly hypoechoic

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Figure 14. 

Rectal Adenocarcinoma. (A) This image illustrates a pronounced asymmetric thickening of the rectal walls with the lumen in an eccentric position. The thickening has a markedly heterogeneous echostructure. (B) This image focuses on the same area of thickening, revealing the presence of intralesional vascular signals, clearly delineated using microflow imaging

A comprehensive overview of the main advantages and disadvantages of GIUS is summarized in Table 1.

Table 1.

This table outlines the advantages and disadvantages of using GIUS for various gastrointestinal conditions, highlighting its diagnostic strengths and limitations compared to other imaging methods

Condition	Advantages of GIUS	Disadvantages of GIUS
Acute appendicitis	Highly effective in children and thin adults Can visualize the inflamed appendix, assess for free fluid and local fat inflammation Can rule out other causes of right lower quadrant pain	May miss appendix if retrocecal Less sensitive than CT
Acute diverticulitis	Rapid assessment tool that helps identify inflamed diverticula and complications such as abscesses or perforations Useful in settings where immediate CT is unavailable	Less detailed than CT, particularly in obese patients or in visualizing smaller abscesses
Small bowel obstruction	Can quickly identify dilated bowel loops and the presence of fluid, potentially pinpointing the location of the obstruction Real-time evaluation of bowel peristalsis can help differentiate between mechanical ileus and paralytic ileus Ideal for serial examinations due to lack of radiation	Limited in differentiating between simple and strangulated obstructions; less detailed than CT in identifying the exact cause or level of obstruction
Intestinal ischemia	Can rapidly detect signs of ischemia such as bowel wall thickening and free fluid; useful for initial bedside evaluation CEUS can demonstrate the absence of vascularization in the thickened intestinal tract, providing critical information on the extent of ischemia	May not identify the cause of ischemia, such as arterial emboli or venous thrombosis Less sensitive and specific than CT
Intestinal perforation	Quick to perform and can identify free intra-abdominal air and fluid indicating perforation, guiding urgent surgical intervention Can also adeptly detect small air bubbles anterior to the liver	Less sensitive in detecting localized perforations compared to CT Less effective in pinpointing the exact location of the perforation compared to CT
Crohn’s disease	Useful in detecting and monitoring bowel wall thickening, abscesses, and other complications Non-radiative and can be repeated frequently for follow-ups	Less effective than MRI in visualizing deep structures and assessing fistulae or the full extent of intestinal involvement
Ulcerative colitis	Can assess bowel wall thickness and vascularization during flares and can be useful for quick evaluations during symptomatic periods	Does not provide detailed mucosal imaging as endoscopy and has limited utility in assessing deep ulcerations
Infectious enteritis	Quick, non-invasive assessment tool to evaluate bowel wall thickening and to differentiate from other causes of acute abdominal pain	Not specific for identifying pathogens Limited use in mild or early disease
Malabsorption and celiac disease	Helps identify complications such as bowel thickening, intussusception, or lymphoma in advanced cases	Not diagnostic for celiac disease or other specific malabsorption disorders
Masses and neoplastic lesions	Can quickly detect the presence and location of masses Useful for initial assessment and guiding further diagnostic procedures	Limited in characterizing the nature of lesions compared to CT, MRI and endoscopy, particularly with deep or small lesions
Common to all conditions	No radiation exposure (particularly beneficial for pediatric populations) Can be performed bedside during the clinical evaluation Can be frequently repeated for necessary follow-ups	Limited effectiveness in obese patients Highly operator-dependent

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CEUS: contrast-enhanced ultrasound; GIUS: gastro-intestinal ultrasound