Ultrasound of the gastrointestinal tract: signs of common disorders

Ultrasound examination of the gastrointestinal tract has become a routine tool for primary imaging in cases of abdominal pain, bowel disturbances, and suspected inflammatory, obstructive, and ischemic processes. This method is radiation-free, available at the patient's bedside, and enables assessment of intestinal wall thickness, its layered structure, peristalsis, vascularization using color Doppler, and signs of complications, including fluid, abscesses, and conglomerates. Standardized guidelines from the European Ultrasound Federation clarify scanning technique, landmarks of normal anatomy, and descriptive terminology. [1]

Ultrasound accuracy depends on the technique of graduated compression, the choice of transducer, and systematic examination of all abdominal quadrants, with mandatory assessment of the most painful area. Scanning is performed in longitudinal and transverse projections, with wall thickness measurements performed strictly perpendicularly, separating the hypoechoic muscular layer from the hyperechoic mucosa and serosa. Color Doppler complements the grayscale image and helps differentiate inflammation from fibrosis, as well as identify hyperemia in active disease. [2]

In acute scenarios, such as suspected acute appendicitis, small bowel obstruction, or diverticulitis, ultrasound is often used as a first-line method. This is especially important in children and young women to reduce the number of radiation-exposed examinations. If the imaging findings are inconclusive or if there are warning signs, the method is immediately supplemented with computed tomography or magnetic resonance imaging, depending on the clinical context. [3]

In chronic diseases, particularly inflammatory bowel disease, intestinal ultrasound serves as a convenient tool for dynamically monitoring activity, identifying complications, and assessing treatment response. In recent years, international consensus and practical guidelines have emerged integrating ultrasound into the standard care of such patients, along with endoscopy and laboratory markers. [4]

Technique and Artifacts: How to Obtain a Reproducible Image

The basic protocol includes a segmental examination of the small and large intestines using a high-frequency linear transducer for superficial sections and a convex transducer for deep loops. Graduated compression helps displace gas and bring the intestinal walls closer to the transducer, improving resolution. A systematic tour begins in the right iliac fossa, where the terminal ileum and appendix are most often visualized. [5]

Wall thickness is measured in an area without maximum compression, perpendicular to the wall, excluding the luminal contents. Normally, the wall of the small intestine is typically 2-3 mm thick, while the wall of the large intestine is 3-4 mm thick with moderate distension. Layering and continuity are considered, as loss of layering and pronounced hypoechogenicity often correspond to active inflammation or ischemia. [6]

Peristalsis is assessed visually and, if necessary, using a cineloop. The small intestine is characterized by peristaltic waves and fluid transport, whereas severe obstruction is characterized by pendulum-like movements and cessation of transport distal to the transition zone. If active inflammation or hyperperfusion is suspected, low-velocity color Doppler is performed, which increases sensitivity to small intramural vessels. [7]

Frequent artifacts are associated with gas, incomplete compression, and incorrect scanning angles. To improve visibility, more gel is applied, positional maneuvers are performed, scanning through the liver to the right upper quadrant, and gentle, stepwise compression is used. If persistent limitations persist, additional imaging techniques are used. [8]

Table 1. Intestinal wall thickness and normal values

Segment	Typical thickness at moderate stretch	Comment
Small intestine	up to 2-3 mm	Pronounced layering is normal. [9]
Colon	up to 3-4 mm	More variability across segments. [10]
Terminal ileum	up to 3 mm	More commonly assessed in Crohn's disease.[11]
Rectum	up to 4 mm	Endoanal examination is targeted. [12]

Acute appendicitis: key ultrasound criteria

The classic ultrasound image includes a non-visualizable lumen and a non-compressible tubular structure originating from the cecum, with a maximum outer diameter greater than 6 mm when compressed by the transducer. Additional features enhance accuracy: hyperechoic infiltration of the surrounding tissue, wall thickening greater than 3 mm, the presence of an appendicolith, localized tenderness under the transducer, and increased blood flow on color Doppler. [13]

In children and young women, ultrasound is recommended as a first-line method. If the results are inconclusive, the next step is computed tomography with contrast or magnetic resonance imaging in special situations, such as pregnancy. International guidelines emphasize that interpretation should take into account clinical scales and laboratory data. [14]

As inflammation progresses, periappendiceal fluid collections, phlegmon or abscess, ruptures in the wall layering, and areas of necrosis are detected, requiring immediate correction of tactics. These findings determine the need for surgical intervention or drainage, as well as the initiation of empirical antibacterial therapy according to local protocols. [15]

Even with apparently normal appendiceal thickness, the combination of severe tenderness upon compression and hyperechoic perifocal tissue increases the likelihood of early appendicitis. In questionable cases in adults, the threshold for CT scanning should be low to avoid delays in treatment. [16]

Table 2. Ultrasound signs of acute appendicitis

Sign	Threshold or description	Diagnostic value
Outside diameter under compression	>6 mm	Basic criterion. [17]
Non-compressibility	No collapse of walls	Increases the likelihood of diagnosis. [18]
Periappendicular tissue	Hyperechogenicity, thickening	Sign of inflammation. [19]
Appendicolitis	Echogenic shadow in the lumen	Associated with complications.[20]
Doppler	Increased blood flow to the wall	Sign of activity. [21]

Small bowel obstruction: how to recognize and stage it

Mechanical obstruction is characterized by dilation of the proximal loops by more than 25 mm, pendulum-like peristalsis with back-and-forth movement of contents, a high fluid level in the lumen, and thin, collapsed distal loops. Identification of a transition zone where dilated loops give way to collapsed ones increases diagnostic confidence. [22]

The more severe the dilation, the higher the risk of ischemia, especially in the absence of normal peristalsis and decreased mural blood flow as measured by color Doppler. Free fluid, wall thickening, and the phenomenon of "mesenteric twisting" suggest strangulation and require urgent surgical intervention. Ultrasound is useful for serial, repeated assessments at the patient's bedside. [23]

The method is highly accurate in the hands of trained emergency department specialists and can expedite patient routing. However, if the level of obstruction is uncertain, ischemia is suspected, or the anatomy is complex, contrast-enhanced CT scanning is indicated to determine the cause and extent of intervention. [24]

In functional conditions, such as paresis, diffuse moderate dilation without a distinct transition zone predominates; peristalsis is reduced, but a closed segment does not form. A combination of echographic signs and clinical data allows for differentiation between mechanical and functional obstruction. [25]

Table 3. Diagnostic thresholds and predictors of severity in small bowel obstruction

Sign	Threshold	Interpretation
Small intestinal loop diameter	≥25 mm	A reliable criterion for dilation. [26]
Peristalsis	Pendulum-like, "back and forth"	Typical for a high block level. [27]
Transition zone	Visualization	Confirms the mechanical nature. [28]
Free liquid	Availability	Risk of strangulation and ischemia. [29]
Blood flow of the wall	Reduced or absent	Sign of ischemia, urgent tactics. [30]

Colonic diverticulitis: ultrasound capabilities

In uncomplicated diverticulitis, thickening of the colonic wall, hyperechoic perifocal tissue, and hypoechoic diverticula with acoustic artifacts are visualized. According to current data, ultrasound can demonstrate sensitivity and specificity comparable to computed tomography in mild and locally complicated cases, especially in the hands of an experienced operator. [31]

This method is applicable in outpatient practice for selecting patients suitable for conservative treatment and for dynamic monitoring during the first days of therapy. Computed tomography is advisable in cases of suspected large abscesses, gas in the venous system, diffuse peritonitis, and in cases of ambiguous ultrasound findings. This stepwise approach reduces radiation exposure without compromising outcomes. [32]

Sonographic signs of complications include perifocal fluid collections, hypoechoic cavities with internal echogenic content, fistulas, and a pronounced reaction of surrounding tissues. Timely identification of these signs determines the need for drainage, escalation of antibacterial therapy, or surgical intervention. [33]

It should be noted that in some patients, changes are minimal in the early stages, and a follow-up examination after 24-48 hours increases detection. Combining ultrasound with clinical assessment and laboratory markers allows for more accurate risk stratification and avoidance of unnecessary hospitalizations. [34]

Table 4. Ultrasound landmarks in diverticulitis

Sign	A typical find	Tactics
Segmental wall thickening	Most often 4-6 mm	Outpatient therapy in stable condition. [35]
Perifocal tissue	Hyperechoic infiltration	Sign of active inflammation. [36]
Abscess	Hypoechoic cavity with echo content	Drainage and escalation of treatment. [37]
Doubts about the diagnosis	An unconvincing picture	Computed tomography. [38]

Intussusception in Children: Rapid Echo Signs

In children, ultrasound is the test of choice when intussusception is suspected. A cross-sectional image reveals a characteristic "target" or "donut" pattern formed by concentric rings of the wall of the retracted segment and the surrounding intestine. Longitudinal sections reveal a "sandwich" pattern, corresponding to the longitudinal overlap of the walls. [39]

Additional signs include enlarged mesenteric fat, enlarged lymph nodes, and sometimes a small amount of free fluid. Early diagnosis is crucial, as successful non-surgical reduction under radiographic or surgical guidance may be possible within the first few hours.[40]

With prolonged progression and signs of ischemia, the risk of requiring surgery increases. Ultrasound helps monitor the effectiveness of straightening attempts and promptly detect recurrence of intussusception, which occurs in some patients. Repeated short examinations at the child's bedside are safe and informative. [41]

The differential diagnosis includes hypertrophic pyloric stenosis in infants with intractable vomiting, gastroenteritis, and other causes of pain. Each scenario has its own ultrasound thresholds, which facilitates routing and reduces unnecessary examinations with ionizing radiation. [42]

Table 5. Intussusception in children: key ultrasound signs

Sign	Description	Clinical significance
"Target" on a cross section	Concentric rings	A highly specific feature. [43]
Sandwich on a longitudinal section	Layered overlay	Complements diagnostics. [44]
Mesenteric tissue and nodes	Hyperechoic tissue, lymphadenopathy	Often accompanying. [45]
Free liquid	A small amount	If there is excess, suspect ischemia. [46]

Hypertrophic pyloric stenosis in infants: measurement thresholds

Hypertrophic pyloric stenosis is characterized by thickening of the pyloric muscular layer and elongation of the canal, which impedes the evacuation of gastric contents. Ultrasound is the standard diagnostic method due to its high accuracy and non-invasiveness. With proper technique, a thickened hypoechoic muscular layer and a narrowed hyperechoic lumen are visualized. [47]

The most commonly used thresholds include a muscular layer thickness greater than 3 mm and a canal length greater than 15-17 mm. Additionally, a transverse diameter greater than 14 mm and a pyloric volume greater than 1.5 cm³ are assessed. These figures should be interpreted taking into account the child's age and body weight, as well as the measurement technique. [48]

Some modern studies discuss lowering the length thresholds to 10-14 mm and the muscle layer thickness to just over 2 mm in early forms; however, such criteria are sensitive to measurement errors and require strict adherence to methodology. In real-world practice, most centers retain traditional thresholds as more stable. [49]

Following ultrasound confirmation, management includes correction of fluid and electrolyte imbalances and referral for surgical treatment. Postoperative ultrasound monitoring is usually not required if clinical signs regress. [50]

Table 6. Diagnostic thresholds for pyloric stenosis

Parameter	Threshold	Note
Thickness of the muscle layer	>3 mm	The most accurate criterion. [51]
Channel length	>15-17 mm	A widely used threshold.[52]
Transverse diameter	>14 mm	Adds length and thickness. [53]
Alternative early thresholds	Length>10-14 mm, thickness>2.2 mm	Requires careful interpretation. [54]

Inflammatory bowel disease: activity, complications, monitoring

In Crohn's disease and ulcerative colitis, ultrasound allows assessment of wall thickness, integrity of layering, vascularization, the presence of ulcers, adipose tissue infiltration, and regional lymphadenopathy. Wall thickening greater than 3 mm in Crohn's disease, loss of layering, and hyperemia on Doppler correlate with inflammatory activity and endoscopic findings. [55]

Current interdisciplinary guidelines from the European Crohn's and Colitis Organization, in collaboration with radiologists and ultrasound societies, reinforce the role of intestinal ultrasound in diagnostics and monitoring, including postoperative scenarios and special situations. The method is applicable for monitoring the response to therapy and the early detection of complications such as strictures, fistulas, and abscesses. [56]

Phenotypic differences between Crohn's disease and ulcerative colitis are also reflected on ultrasound. In Crohn's disease, the terminal ileum is more frequently affected, with segmental lesions, transmurality, hyperemia, and fibrosis noted over time. In ulcerative colitis, lesions are limited to the mucosa and submucosa, are more extensive, and are distributed proximally from the rectum. [57]

To detect strictures during observation, a combination of wall thickening greater than 3 mm, persistent lumen narrowing, and proximally positioned dilated loops, as well as decreased perfusion due to fibrosis, are considered. Consensus is emerging on ultrasound staging of strictures, which helps guide the choice between escalating anti-inflammatory therapy and endoscopic or surgical correction. [58]

Table 7. Ultrasound in Crohn's disease and ulcerative colitis

Parameter	Crohn's disease	Ulcerative colitis
Wall thickness	Often 5-15 mm	Moderately elevated in the affected segment
Layering	Often lost during activity	Often preserved longer
Vascularization	Increased with activity	Increased with activity
Complications	Strictures, fistulas, abscesses	Toxic dilatation, severe bleeding
Sources	[59]	[60]

Ischemic colitis: warning signs

Ischemic colonic lesions may present with segmental wall thickening, hypoechogenicity, and disrupted stratification, all accompanied by decreased perfusion. In severe cases, signs of intramural hemorrhage and free fluid may be present. These findings are nonspecific and require clinical and laboratory correlation and confirmation by other methods. [61]

Ultrasound is particularly useful for bedside assessment in patients with limited mobility and in those for whom contrast is contraindicated. In the acute phase, repeated short studies allow monitoring of blood flow dynamics and wall thickness. If total ischemia or necrosis is suspected, urgent CT scanning and surgical consultation are necessary. [62]

Historical case series demonstrate the value of ultrasound in detecting colonic ischemia, but without clear specific thresholds. Therefore, the method should be considered as part of a multiparametric algorithm with priority given to rapid, decisive studies. [63]

The risk of ischemia is higher in older adults, those with cardiovascular disease, episodes of hypotension, and after major vascular surgery. Understanding these factors helps to correctly interpret moderate ultrasound changes and avoid delaying diagnostic escalation. [64]

Table 8. Echo signs of ischemic colitis and tactics

Sign	Ultrasound finding	Action
Wall thickness	Moderately elevated, hypoechoic	Urgent risk stratification. [65]
Layering	Violated	Suspected severe course. [66]
Perfusion	Decreased according to Doppler	Indication for advanced imaging. [67]
Free liquid	Availability	Increases the risk of necrosis. [68]

Quick Algorithms for Choosing a Method: When Ultrasound is Sufficient and When It Isn't

In a typical presentation of acute appendicitis in a child or young woman, a visualized non-compressible appendix greater than 6 mm and perifocal infiltration are sufficient for ultrasound to initiate treatment. In adults, if there is any doubt or a high probability of alternative pathology, computed tomography is advisable. This cascade approach is supported by specialized guidelines. [69]

When small bowel obstruction is suspected, ultrasound quickly reveals the presence of dilation and a transition zone and helps identify high-risk groups for ischemia. However, CT scanning is more often required to determine the cause and extent of obstruction, especially if strangulation is suspected. [70]

In uncomplicated diverticulitis in a stable patient, ultrasound is sufficient to confirm the diagnosis and initiate conservative therapy. If signs of abscess formation, fistulas, or peritonitis appear, computed tomography is preferred as a first step for planning intervention. [71]

In patients with inflammatory bowel disease, ultrasound serves as a tool for routine monitoring of activity and complications. It complements endoscopy and laboratory markers and is recommended by leading European societies as part of the standard of care. [72]

Table 9. Which method to choose in typical clinical scenarios

Scenario	First line	When to escalate
Suspected appendicitis in a child or young woman	Ultrasound	In case of uncertainty or complications, proceed to computed tomography or magnetic resonance imaging. [73]
Suspected small bowel obstruction	Ultrasound	Confirmation of cause and stage by CT scanning, especially in cases of ischemic risk. [74]
Uncomplicated diverticulitis in a stable patient	Ultrasound	Computed tomography if abscess, fistula, peritonitis is suspected. [75]
Monitoring inflammatory bowel disease	Ultrasound	Magnetic resonance imaging or computed tomography in case of complications and unclear picture. [76]

Limitations of the method and how to compensate for them

Ultrasound is limited in cases of excess gas, obesity, deep retroperitoneal regions, and when visualizing extended loops in hard-to-reach areas is necessary. In these cases, stepwise compression, positional maneuvers, and the transition to complementary imaging techniques are helpful. Effectiveness depends significantly on the experience of the specialist, as emphasized by ultrasound societies. [77]

This method does not always reliably differentiate severe inflammatory stenosis from fibrous stenosis without the aid of elastography, contrast enhancement, and magnetic resonance imaging. Therefore, in cases of persistent stenosis without signs of hyperemia and with symptoms of subcompensated obstruction, the decision on tactics is made through a multidisciplinary approach. [78]

Some numerical thresholds, such as those for pyloric stenosis in infants, are sensitive to measurement technique and distension conditions. In questionable cases, it is preferable to repeat the study with an experienced specialist, verify with the clinic and laboratory, and, if necessary, consider alternative methods. [79]

Finally, in the presence of ischemia and suspected intestinal wall necrosis, any delay is dangerous. Even a convincing ultrasound image requires immediate escalation of diagnostics and treatment, since the patient's fate is determined by the time to revascularization or resection. [80]