Pal P, Mateen MA, Pooja K, Rajadurai N, Gupta R, Tandan M, Duvvuru NR. Intestinal ultrasound in Crohn’s disease: A systematic review of its role in diagnosis, monitoring, and treatment response. World J Meta-Anal 2025; 13(2): 104080 [DOI: 10.13105/wjma.v13.i2.104080]
Corresponding Author of This Article
Partha Pal, Department of Medical Gastroenterology, Asian Institute of Gastroenterology, 6-3-661 Red Rose Cafe Lane, Sangeet Nagar, Somajiguda, Hyderabad 500082, India. partha0123456789@gmail.com
Research Domain of This Article
Gastroenterology & Hepatology
Article-Type of This Article
Systematic Reviews
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This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Partha Pal, Kanapuram Pooja, Nandhakumar Rajadurai, Rajesh Gupta, Manu Tandan, Nageshwar Reddy Duvvuru, Department of Medical Gastroenterology, Asian Institute of Gastroenterology, Hyderabad 500082, India
Mohammad Abdul Mateen, Department of Diagnostic Radiology and Imaging, Asian Institute of Gastroenterology, Hyderabad 500082, India
Author contributions: Pal P conceptualized the work, performed the literature search, wrote the first draft, and provided intellectual input; Mateen MA conceptualized the work, supervised the writing and critically revised the manuscript; Pooja K performed literature search, wrote the first draft and revised the manuscript; Rajadurai N performed literature search and helped in writing the first draft; Gupta R supervised the literature search, and the writing, provided intellectual input and critically revised the manuscript; Tandan M supervised the literature search, and the writing, provided intellectual input and critically revised the manuscript; Duvvuru NR supervised the writing, provided intellectual input and critically revised the manuscript.
Conflict-of-interest statement: None of the authors have relevant conflicts of interest to declare.
PRISMA 2009 Checklist statement: The authors have read the PRISMA 2009 Checklist, and the manuscript was prepared and revised according to the PRISMA 2009 Checklist.
Open Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Partha Pal, Department of Medical Gastroenterology, Asian Institute of Gastroenterology, 6-3-661 Red Rose Cafe Lane, Sangeet Nagar, Somajiguda, Hyderabad 500082, India. partha0123456789@gmail.com
Received: December 10, 2024 Revised: February 26, 2025 Accepted: April 17, 2025 Published online: June 18, 2025 Processing time: 189 Days and 3.3 Hours
Abstract
BACKGROUND
Intestinal ultrasound (IUS) has gained prominence as a safe, non-invasive imaging technique for managing Crohn’s disease (CD), offering real-time evaluation without radiation exposure.
AIM
To systematically review the role of IUS in diagnosing, monitoring disease progression, assessing treatment response, and managing complications in CD.
METHODS
A literature search of PubMed and Embase databases was conducted, identifying 207 original research articles published between 1953 and June 2024. The review focused on diagnostic accuracy, disease monitoring, therapeutic utility, and advancements in IUS applications.
RESULTS
IUS has shown high diagnostic accuracy for detecting inflammation, particularly in the ileum and colon, with limitations in jejunal and rectal regions. It is effective in assessing disease activity using parameters like bowel wall thickness (BWT) and vascularity and correlates well with endoscopy and magnetic resonance enterography. IUS can predict early response to biologics, with reductions in BWT serving as an important marker. In known CD, IUS influences clinical decisions during remission, flares, and therapy evaluations. It reliably detects strictures, fistulas, and therapy-related complications. Small intestinal contrast ultrasound (SICUS) can improve the detection of strictures particularly proximal ones. Techniques such as CE-IUS and elastography enhance stricture characterization but require further validation. IUS is also useful in special scenarios like perianal fistulas, pregnancy, post-operative CD, and guiding endoscopic therapy.
CONCLUSION
IUS is a patient-friendly, cost-effective imaging tool that significantly impacts CD management across various stages. Its integration into clinical practice supports early diagnosis, disease monitoring, and therapeutic adjustments. Further studies are warranted to refine advanced techniques and standardize its application for broader use.
Core Tip: Intestinal ultrasound (IUS) is a dynamic, non-invasive imaging tool for Crohn’s disease (CD). It accurately evaluates transmural and extramural complications, with capabilities comparable to magnetic resonance enterography. While these modalities remain necessary for proximal strictures, skip lesions, and extra-intestinal disease, IUS serves as an excellent initial screening option in suspected cases. In established CD, IUS guides clinical decisions during remission, flares, and therapeutic response monitoring. It identifies complications, including strictures and fistulas, with advanced methods like elastography aiding stricture characterization. Additionally, IUS is invaluable in special cases such as perianal fistulas, pregnancy, post-operative CD, and guiding therapeutic interventions.
Citation: Pal P, Mateen MA, Pooja K, Rajadurai N, Gupta R, Tandan M, Duvvuru NR. Intestinal ultrasound in Crohn’s disease: A systematic review of its role in diagnosis, monitoring, and treatment response. World J Meta-Anal 2025; 13(2): 104080
Inflammatory bowel diseases (IBD), comprising Crohn’s disease (CD) and ulcerative colitis (UC), are chronic conditions marked by inflammation of the gastrointestinal tract with distinct patterns of involvement. CD is a relapsing and remitting condition characterized by transmural inflammation that can affect the entire gastrointestinal tract, leading to diverse presentations ranging from mild inflammation to severe complications such as strictures, fistulas, and abscesses. These complications pose significant diagnostic and therapeutic challenges, necessitating accurate and versatile imaging tools.
In recent years, intestinal ultrasound (IUS) has emerged as a valuable, non-invasive imaging modality for managing CD. Unlike traditional imaging techniques such as magnetic resonance enterography (MRE) or computed tomography enterography (CTE), IUS offers several advantages, including the absence of radiation, cost-effectiveness, and real-time visualization of transmural and extramural disease. It is suitable for repeated evaluations at the point of care, making it highly practical for disease monitoring and management. IUS is particularly useful across various stages of CD, serving as an initial diagnostic screening tool, assessing disease activity, monitoring therapeutic response, and evaluating complications such as strictures and fistulas[1-3]. Advanced techniques like small intestinal contrast ultrasound (SICUS), contrast-enhanced ultrasound (CEUS) and elastography further enhance its capabilities, particularly in stricture detection, characterization by distinguishing inflammatory from fibrotic lesions.
Despite its expanding role, IUS has limitations, such as reduced sensitivity for detecting jejunal and rectal lesions and a lack of standardization in scoring systems and operator training. However, IUS is highly effective in CD to evaluate transmural involvement and complications in contrast to UC limited to mucosal and submucosal layers, except in severe cases[2,4-7]. This review explores the clinical applications of IUS in CD, emphasizing its advantages, limitations, and potential for further research to optimize its integration into routine practice.
MATERIALS AND METHODS
Search strategy
For the purpose of the review, we searched the PubMed and Embase with the following search criteria: (‘intestinal ultrasound'/exp OR 'intestinal ultrasound' OR 'bowel ultrasound'/exp OR 'bowel ultrasound' OR 'transabdominal ultrasound'/exp OR 'transabdominal ultrasound’ OR ‘ultrasound’ OR ‘sonography’) AND ('ibd' OR 'inflammatory bowel' OR 'crohn disease'/exp OR 'crohn disease’). Additional searches were made using key terms such as ‘small intestinal contrast ultrasound (SICUS)’, ‘contrast enhanced ultrasound (CEUS)’, ‘elastrography’ and ‘transperineal ultrasound’. We found 12936 records between 1953 to June 2024 after excluding duplicates (Partha Pal and Kanapuram Pooja performed search individually, disagreements were resolved by Nandhakumar Rajadurai). We screened all the titles and abstracts including full text of selected articles. Finally 207 original research articles pertaining to IUS were included for scoping review including cross-references excluding review articles/Letter to editors/editorial/pictorial surveys/case reports/narrative reviews/systematic reviews/consensus/articles in language other than English (due to resource constraints)/translational research/articles not focused on the topic (Figure 1, Flow diagram). We summarized the evidence under each subheading based on qualitative review of existing literature. The areas where the literature was substantial, we represented it in a tabular form.
We structured our analysis using the PICO framework, defining the Population (P) as patients with suspected or confirmed CD, the Intervention (I) as intestinal ultrasound (IUS), including SICUS and CEUS, and the Comparator (C) as MRE, CTE, endoscopy, and biomarkers. The Outcomes (O) included diagnostic accuracy, disease extent and activity assessment, differentiation of inflammatory vs fibrotic strictures, detection of complications, monitoring treatment response, and predicting postoperative recurrence. This approach ensures a systematic evaluation of IUS in CD, highlighting its advantages, limitations, and clinical utility.
RESULTS
IUS as a diagnostic strategy in suspected CD
IUS plays a critical role in the diagnosis of CD, particularly in patients presenting with non-specific abdominal pain and altered bowel habits due to functional disorders. Based on four prospective studies, the diagnostic performance of IUS in suspected IBD had sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) ranging from 65%-85%, 80%-98%, 68%-98%, and 58%-92%, respectively. However, variations in the criteria for defining abnormal IUS findings, such as bowel wall thickness (BWT) thresholds, diagnostic reference standards, and ultrasound probe frequencies, contribute to discrepancies in diagnostic accuracy[3,6-8].
The sensitivity of IUS for diagnosing CD is higher (84%) compared to UC, which ranges between 38%-66%[6,7]. Sensitivity was particularly high for detecting inflammation in the ileum, left colon, ascending and transverse colon but remains low for splenic flexure, duodenal, jejunal, and rectal lesions (10%-20%)[3]. Lowering the BWT threshold for abnormal findings from ≥ 7 mm to ≥ 5 mm marginally improves sensitivity but reduces specificity and PPV[7]. Training over time enhances diagnostic accuracy, as shown in a study where sensitivity and specificity for detecting ileocolonic CD improved from 57% to 73% and 76% to 90%, respectively[8].
In cases of non-specific ileitis, normal BWT (< 3 mm) on initial or repeat ultrasound effectively excludes CD[9]. A decision analysis model identified IUS combined with ileo-colonoscopy as the most accurate and cost-effective diagnostic approach for suspected CD[10]. Furthermore, a prospective study from Australia demonstrated that the use of IUS for low-risk gastrointestinal symptoms reduced the need for colonoscopies and gastroenterology consultations[11].
Role of IUS in differentiating IBD from its mimics: A retrospective case control study including confirmed cases of ileocecal CD and Behcet’s disease (BD) showed that large ulcers and focal lesions on IUS favored BD whereas small bowel involvement favored CD[12]. CEUS differentiates colon cancer from IBD by identifying disrupted wall stratification, irregular and delayed enhancement, and prolonged washout[13].
A retrospective study from India involving 76 patients explored a two-step IUS strategy for evaluating chronic diarrhea accompanied by abdominal pain. The approach incorporated shear wave elastography (SWE) and shear wave dispersion (SWD) to classify strictures based on their characteristics: Fibrotic strictures exhibited elevated SWE with normal SWD values, inflammatory strictures showed normal SWE but elevated SWD, and mixed strictures demonstrated increases in both parameters. Further diagnostic distinctions were made based on specific ultrasound findings—CD was associated with features such as fat proliferation, fistula formation, and increased vascularity; UC demonstrated thickened submucosa with preserved wall stratification and high SWD; neoplastic lesions typically presented with BWT > 9 mm and SWE values > 90 kPa. Tuberculosis was suggested by the presence of fluid collections and lymphadenopathy, while infective ileo-colitis and diverticulitis showed either inflammatory or mixed sonographic patterns[14].
Chen et al[15] classified ultrasonographic patterns into four types: Type A (preserved layering, e.g., lupus enteropathy), Type B (thickened wall with disrupted layering, e.g., intestinal tuberculosis), Type C (uniform hyperechoic thickening, e.g., ischemic bowel disease), and Type D (hypoechoic thickening with loss of stratification, e.g., CD. These patterns aid in distinguishing IBD from its mimics but may require clinical correlation.
Another retrospective study found that vascularity alone, without spectral waveform analysis, was insufficient to distinguish inflammatory from neoplastic pathologies, though the highest vascularity was observed in CD and cytomegalovirus colitis[16].
IUS in CD
IUS in CD can detect asymptomatic disease, preclinical relapse and endoscopic activity impacting management in a significant proportion (Table 1)[17-20]. Half of the asymptomatic patients may have active disease on IUS[18,21]. Pedersen et al[22] found that dynamic ultrasound identified bowel wall thickening in 67% of radiologically confirmed CD cases, proving valuable in reducing the need for repeated radiographic studies[22]. Similar to UC, assessment of vascularity using color doppler signal (CDS) was shown to identify active disease[23]. Vascularity according to Limberg score correlate well with endoscopic and surgical macroscopic activity/inflammatory cell infiltration (macrophage/B cell/T cell) vascularity (assessed by factor VIII staining)[24,25]. Goertz et al[26] further highlighted the diagnostic accuracy of IUS, with bowel wall thickening (> 3 mm) and hypervascularity correlating strongly with histological inflammation, particularly in the terminal ileum[26]. A small prospective study (n = 35) showed good correlation with endoscopic and clinical activity with 100% specificity and highest sensitivity in transverse colon (Table 1)[27]. Excellent correlation with endoscopy (80%) and MRE (86.3%) had been shown in a large retrospective study (n = 280)[20].
Table 1 Summary of studies evaluating impact of intestinal ultrasound in the management of Crohn’s disease.
Clinical decisions changed in up to 60% of cases post-IUS compared to before IUS. Half of the patients with clinically asymptomatic disease had active disease on IUS
70% with mild or no endoscopic inflammation on ileo-colonoscopy had moderate to severe disease on IUS. 75% of the above group had significant management changes
SUS-CD and IBUS-SAS scores in IUS were not different between active and inactive disease. Peak intensity in contrast-enhanced IUS correlated well with endoscopic activity (AUC: 0.80)
60% had an impact on disease management and predicted preclinical relapse. Good correlation with MRI (86.3%) and endoscopy (80%). Use of MRI reduced after IUS
Bowel ultrasound score > 3.52, complications (stricture, fistula, abscess), fecal calprotectin ≥ 250 µg/g, and male sex predicted the 12-month course in CD
Color Doppler ultrasound showed increased vascularity in active CD. RI was lower in active vs inactive cases, correlating with clinical and histological activity
Bowel wall thickening (> 3 mm) and hypervascularization strongly correlated with histological inflammation in Crohn’s ileitis. Limberg score had significant correlation with histopathology
Dynamic ultrasound detected bowel wall thickening (target lesions) in 67% of radiologically confirmed CD. Found useful for follow-up to reduce repeated radiographic exams
Assessing vascularity (CEUS): CEUS has demonstrated significant utility in the evaluation and management of CD, with studies highlighting its ability to assess disease activity, differentiate lesion types, and predict therapeutic outcomes (Table 2) [28-33]. CEUS consistently correlates with endoscopic findings, as shown in studies like Białecki et al[34], where peak enhancement > 40.5% and regional blood flow > 54.8 mL/min predicted active inflammation [area under the curve (AUC) = 0.87], and Wang et al[36], which reported sensitivity and specificity of 97.4% and 100%, respectively, for dynamic perfusion parameters[34-36]. The maximum intensity of the inner wall layer (muscularis mucosa and submucosa) on CEUS differs between endoscopically severe vs mild disease[37]. High peak velocity (> 23 dB) with minimal decline on CEUS suggest severe CD due to entrapment of micro-bubbles in inflamed bowel wall for extended period of time[38]. A retrospective study (n = 50) found CEUS to correlate well with endoscopic activity (AUC: 0.80), while routine IUS scores were not predictive of active disease[39]. Contrast harmonic imaging (CHI) with a high-resolution probe minimizes motion artifacts from peristalsis, unlike CDS and hence more valuable for assessing response to therapy and outcomes[40-42]. A prospective study demonstrated that CEUS distinguishes stages of active CD, with Limberg II showing medial wall thickening and enhancement, while Limberg III/IV involve full-wall thickening and enhancement[43].
Table 2 Studies summarizing utility of contrast-enhanced ultrasound in Crohn’s disease activity assessment.
CEUS and dynamic CE-MRE provided complementary insights into stricture stiffness, with CEUS emphasizing inflammatory characteristics
CEUS was also effective in distinguishing inflammatory and fibrotic strictures, with quantitative analyses revealing mean blood flow volumes of 48 ± 10 mL/min in inflammatory vs 15 ± 5 mL/min in fibrotic strictures, achieving an AUC of 0.92[44]. In postoperative CD, CEUS demonstrated sensitivity of 98% and specificity of 100% for detecting recurrence, with hypervascularity correlating with endoscopic scores in 92% of cases[45]. Moreover, CEUS was comparable to magnetic resonance imaging (MRI) in assessing lesion length and wall thickness (r = 0.85 and r = 0.83, respectively) while providing real-time visualization of vascular changes[46,47]. Studies in pediatric CD further validated its specificity for moderate-to-severe disease (100%) and correlation with clinical scores[48]. Additionally, CEUS-guided SWE differentiated fibrotic (elasticity > 90 kPa) from inflammatory strictures (elasticity < 50 kPa), influencing management decisions in 60% of cases[49,50].
Blood flow in visceral artery and CD activity: Earlier studies have even shown that the maximum flow volume and peak systolic velocity in aorta correlate with CD activity index (CDAI)[51]. Another study showed that the superior mesenteric artery (SMA) flow rate was significantly higher in active disease with a shorter splanchnic transit time[52]. Increased SMA blood flow (> 500 mL/min) was shown to be associated with increased wall thickness and vascularity in active small bowel CD with reduction in SMA resistance index[53].
SICUS: SICUS is a radiation-free imaging technique for CD, enhancing small bowel visualization with oral contrast and accurately detecting strictures, fistulas, and disease extent (Table 3). For instance, Hakim et al[54] showed that SICUS has a sensitivity of 98.7% and specificity of 100% in detecting small bowel lesions in pediatric CD, with excellent agreement (κ = 0.84) for strictures compared to MRE[54]. Similarly, Pallotta et al[55] reported that SICUS outperformed conventional IUS in detecting jejunal and ileal lesions, achieving 96% sensitivity in proven pediatric CD[55]. In adult populations, Parente et al[56] demonstrated that SICUS is comparable to barium enteroclysis for assessing disease extent and detecting luminal complications, with an improved inter-observer agreement (IOA) and ability to detect strictures (74% to 89%) and active disease (91% to 96%) post-contrast. SICUS was done 30 minutes after 500-800 mL polyethylene glycol (PEG) ingestion based on the median time for PEG to reach terminal ileum (31.4 minutes)[56]. Onali et al[57] found that SICUS had similar sensitivity and specificity to CTE for identifying strictures, abscesses, and fistulas in surgical CD cases[57].
Table 3 Studies summarizing utility of small intestinal contrast ultrasound in Crohn’s disease.
Sensitivity of 92% for strictures; comparable to CTE for lesions and luminal complications
IUS scoring in CD
IUS scoring systems have demonstrated utility in assessing disease activity in CD, with multiple validated indices providing objective and reliable metrics. Early scores, such as the Ultrasonographic Index of CD, showed correlations with endoscopic findings[58]. Five modern scoring system in CD include: (1) Bowel ultrasound score (BUSS); (2) Simple ultrasound score-CD (SUS-CD); (3) International bowel ultrasound segmental activity score (IBUS-SAS); (4) Simple-US score; and (5) Ultrasound consolidated score (UCS)[59-63]. BUSS, IBUS-SAS, and Simple-US focus on the worst-affected segment, while SUS-CD and UCS assess multiple ileocolonic segments[60]. IBUS-SAS had the strongest correlation with the Simple Endoscopic Score for CD (SES-CD), with a cut-off of 48.7 (AUC: 0.895, sensitivity: 85.4%, specificity: 82.4%) in retrospective validation and 25.2 (AUC: 0.95, sensitivity: 82.2%, specificity: 100%) in prospective studies (Wang et al[66]). (Table 4)[64-66]. Post-hoc analysis of the METRIC trial demonstrated higher sensitivity for SUS-CD but greater specificity for BUSS[67].
Table 4 Studies evaluating scoring systems to assess disease activity in inflammatory bowel diseases based on intestinal ultrasound.
Ultrasound activity index based on wall thickness and Doppler correlated well with SES-CD (AUC: 0.92)
In a study by Xu et al[68], IBUS-SAS correlated strongly with the Magnetic Resonance Index of Activity (MARIA) score (r = 0.86) and SES-CD (r = 0.82), showing comparable diagnostic accuracy for active disease. The IBUS-SAS cut-off of 46.7 achieved an AUC of 0.86, demonstrating high reliability[68]. Wang et al[69] demonstrated IBUS-SAS reductions after infliximab therapy, correlating with clinical and endoscopic responses in pediatric CD[69]. These findings underscore the evolving role of IUS scores in guiding clinical decision-making and monitoring therapeutic outcomes in CD.
New models integrating biomarkers (ESR and albumin) with IUS parameters have shown promise, predicting mucosal activity = 2X ESR + 9.3 X (sum of product of Limberg score and BWT in each bowel segment, AUC: 0.93) and transmural activity (= -1.3X albumin+ 1.7X sum of Limberg scores in each bowel segments, AUC: 0.85)[70]. Fukushima et al[71] utilized the US-CD scoring system, incorporating BWT, CDS, mesenteric fat echogenicity, stratification, and stenosis. A US-CD score ≥ 11 predicted clinical relapse and the need for endoscopic balloon dilation, while a score ≥ 6 was associated with the need for enhanced treatment[71].
Elastography and contrast ultrasound in CD stricture characterization
Earlier studies showed that a stratified echo pattern of stricture signified fibrotic stricture whereas hypoechoic pattern and vascularization signified predominantly inflammatory stricture[4,72,73]. A small pre-surgical study (n = 12) found submucosal hypo-echogenicity and mucosal thickness indicative of fibrosis, while mesenteric fat echogenicity and mural changes predicted chronic and acute inflammation[74]. Multi-modality ultrasound using elastography and contrast enhanced sonography have been shown to be useful in differentiating fibrotic and inflammatory strictures however they lacks validation and standardization based on machine specific settings[75].
Elastography: Elastography has emerged as a vital tool in differentiating fibrotic from inflammatory strictures in CD. Strain on ultrasound elastography measures tissue deformability, with a higher strain ratio indicating increased stiffness and fibrosis[76]. Fibrotic strictures with high strain ratios (≥ 2) are less responsive to anti-TNF therapy and negatively predict transmural healing (TH) however other study showed conflicting results (Table 5)[77,78]. A small study (n-10) sowed that real time elastography assessed strain correlated with collagen content on surgical specimen[79].
Table 5 Summary of studies evaluating role of intestinal ultrasound elastography in characterizing strictures in Crohn’s disease.
23 ileal or ileocolonic CD for surgery (20 inflammatory CD as controls)
Quantitative strain ratio in ileum
Cross sectional
Higher strain ratio indicated higher ileal fibrosis based on semiquantitative and quantitative analysis (Masson’s trichrome staining). Excellent inter-rater agreement for assessing strain ratio
22.55 KPa was the cut-off in discriminating mild-moderate vs severe fibrosis (AUC 0.822). Vascularization (Limberg III/IV) predicted severe inflammation vs mild-moderate inflammation (AUC 0.811)
Inverse correlation between strain ratio at baseline and thickness variations on anti-TNF therapy at 12 and 52 weeks. Baseline strain ratio lower in patients with transmural healing
No correlation between inflammation and fibrosis on histology with contrast-enhanced ultrasound (r = 0.16, P = 0.45 for inflammation and r = -0.28, P = 0.19 for fibrosis)
Strong correlation noted between fibrocyte numbers and ARFI on IUS (R = 0.8383). High fibrocyte number associated with escalation of medical therapy and endoscopic/surgical treatment at 30 months follow-up
Bowel stiffness correlated strongly with histopathology, including fibrosis and chronic inflammation (r > 0.69, P < 0.001)
A prospective study by Chen et al[80] demonstrated that bowel stiffness assessed via SWE was a strong predictor of disease progression, with a cutoff of > 12.75 kPa correlating with stricturing or penetrating disease (AUC: 0.792). Another study (Zhang et al[81]) showed different cut off: > 21 KPa predict fibrotic strictures, AUC: 0.877). Similarly, Zhao et al[82] highlighted that stiffness values strongly correlated with histopathological fibrosis scores (r > 0.69, P < 0.001). Takeuchi et al[83] validated SWE as an effective method for predicting the degree of bowel fibrosis, offering high accuracy in differentiating inflammatory from fibrotic lesions.
A recent study have shown strong correlation of circulating fibrocyte numbers with acoustic radiation force impulse (ARFI) and need for escalation of therapy on IUS[84]. Among all 3 modalities of SWE, SWE was shown to be better than strain elastography and ARFI for stricture characterization (Table 5)[85].
CEUS: CEUS has demonstrated varying success in distinguishing fibrotic from inflammatory strictures (Table 6). Kratzer et al[86] validated CEUS for identifying fibrotic strictures through surgical/histologic findings in a small cohort (n = 11). Ripollés et al[31] showed a significant correlation between increased contrast enhancement and pathological inflammatory scores based on histopathology. Wilkens et al[87] (2018) reported that CEUS accurately detected inflammation but lacked correlation with fibrosis histology (r = -0.28, P = 0.19). Zhao et al[82] emphasized CEUS's utility in identifying chronic inflammation and differentiating fibrotic strictures using dynamic enhancement parameters. A pharmacokinetic model study found that inflammatory strictures had higher blood flow and volume but similar mean transit times compared to fibrotic strictures, with inflammatory strictures showing greater maximum enhancement and area under the enhancement curve[44]. Moreover, CEUS parameters like peak enhancement (> 40.5%) and regional blood flow were significantly associated with active inflammation[34]. However another study showed that percentage increase in maximum enhancement and area under the enhancement curve was higher in inflammatory strictures whereas time to maximal enhancement was not significantly different[88]. Conflicting evidence exists, as a study reported that relative contrast enhancement on CEUS could not effectively differentiate inflammatory from fibrotic strictures[85].
Table 6 Summary of studies evaluating role of contrast enhanced ultrasound in characterizing strictures in Crohn’s disease.
CEUS correctly classified 23/28 segments based on histopathological inflammation or fibrostenosis with substantial agreement (kappa = 0.632)
IUS for complications of CD: IUS is a reliable tool for identifying complications of CD, including strictures, fistulas, and abscesses, with consistently high diagnostic accuracy. Neye et al[89] demonstrated IUS's sensitivity (78%-90%), specificity (90%-99%), PPV (83%-90%), and NPV (91%-99%) for these complications, confirming its effectiveness as a non-invasive diagnostic modality[89]. Studies such as Maconi et al[90] highlighted IUS's higher sensitivity for detecting ileal strictures (84.6%) compared to colonic strictures (58.8%) and moderate sensitivity for enteroenteric fistulas (50%). Combining IUS with barium studies further improved diagnostic accuracy for internal fistulas to 91.4% (Maconi et al[91]). Furthermore, Moreno et al[92] demonstrated IUS's utility in monitoring fistula progression, detecting 67.4% of cases during disease progression and informing treatment strategies. Ripollés et al[93] demonstrated CEUS's 100% specificity and 98.2% accuracy in differentiating abscesses (≥ 3 cm, non-enhancing) from phlegmons (enhancing) aiding surgical decision making. Wang et al[94] showed that trans-abdominal ultrasound (TAUS) closely approximates water-immersion ultrasound for detecting Crohn's lesions, with substantial agreement (kappa: 0.446–0.615). TAUS accurately identified fistulas (accuracy: 92.7%, specificity: 96%) and moderately detected fat wrapping and mucosal irregularities.
Mesenteric fat on IUS in CD: A retrospective study has shown that mesenteric adipose tissue alteration in IUS was correlated with biochemical marker (C reactive protein), clinical indices (CDAI), length and thickness of diseased bowel, and internal fistulas. In quiescent CD, mesenteric hypertrophy was not a risk factor for relapse[95].
Monitoring therapeutic response with IUS in CD
IUS predicting response to biologic therapy: IUS has emerged as a reliable tool to predict therapeutic response to biologic agents in CD. Several studies demonstrate its ability to distinguish responders from non-responders early, predict endoscopic response/remission, and assess long-term outcomes (Table 7). Consistent IUS parameters such as BWT, vascularity, and advanced modalities like elastography and CEUS have shown high predictive value (Table 2)[78,96-107].
Table 7 Role of intestinal ultrasound in predicting response to biologic therapy.
Lower infliximab trough level was associated with higher CDS in both UC and CD. Transmural healing in CD was associated with higher infliximab trough levels
Early IUS changes predicting response: Hoffmann et al[108] showed that reductions in BWT ≥ 1 mm by week 8 of ustekinumab therapy correlated with clinical (CDAI ≥ 70 reduction) and biochemical [C-reactive protein (CRP) ≥ 0.5 mg/dL reduction] improvements[108]. Similarly, early reductions in BWT, CDS, and SWE at 4-8 weeks were associated with endoscopic response at 12-34 weeks in a prospective study and at 48 weeks in a post-hoc analysis of the STARDUST trial[105,109]. IUS response was highest in biologic naive patients and in colon while on ustekinumab in a post-hoc analysis of the STARDUST trial[109]. Changes in these parameters as early as week 2 were identified in responders by Chen et al[4], highlighting their ability to guide early treatment decisions.
Correlation between IUS and endoscopic/clinical remission: Sonographic normalization strongly correlated with endoscopic remission and clinical response[96,97]. BWT ≤ 4 mm was associated with treatment success and biologic retention[99,100]. Another study showed that BWT cut off of 3.2 mm at 12-34 weeks was most accurate for predicting endoscopic remission at same time point[105]. A prospective study noted that TH occurred in 42.4% of patients at one year and was associated with steroid-free remission and reduced need for surgery (Paredes et al[98]). Allocca et al[110] demonstrated that BUSS ≤ 3.52 at week 12 strongly predicted endoscopic remission [odds ratio (OR) = 9.93, P < 0.001], and the IBUS-SAS threshold of ≤ 22.8 exhibited high diagnostic accuracy (AUC = 0.906). A prospective study by showed that IUS based tight control strategy improved endoscopic remission rates[111].
Role of advanced IUS modalities (SWE and CEUS): SWE provides additional insights into treatment response. Dolinger et al[112] showed that SWE changes effectively predicted therapeutic outcomes in pediatric CD. Strain ratio ≥ 2, based on SWE, predicted the need for surgery due to fibrotic strictures[77,78].
In contrast, CEUS demonstrated limited incremental benefits, though CEUS washout rates enhanced prediction of endoscopic response in certain cases[105]. Guidi et al[113] found CEUS bowel wall enhancement correlated strongly with inflammatory markers in infliximab-treated patients[113]. CEUS performed 1 month after starting steroid or anti-TNF therapy, perfusion analysis of the intestinal wall (peak enhancement, rate of wash in/wash out and area under time-intensity curve in wash in phase) can predict treatment response[114]. Another small prospective study showed that there was greater reduction in peak intensity, area under curve, slope of wash in and mean transit time in responders compared to who relapsed within 6 months[102]. Ainora et al[115] focused on multimodality assessments during ustekinumab therapy and reported that early changes in IUS parameters, combined with other imaging and laboratory findings, could refine therapeutic strategies during biologic induction.
IUS and biologic trough levels: Biologic trough levels correlated well with ultrasonographic response. Han et al[103] reported that infliximab levels > 5 mcg/mL and adalimumab levels > 10.5 mcg/mL were associated with ultrasonographic improvement. Higher adalimumab trough levels (> 3 µg/mL) correlated with lower BWT in the terminal ileum and colon, predicting better biologic retention[100]. Similarly, higher infliximab trough levels were linked with TH in CD[107].
Correlation with biomarkers (e.g., fecal calprotectin/CRP): The integration of IUS with biomarkers such as fecal calprotectin (FCP) and CRP offers a robust, non-invasive approach to monitor CD activity (Table 8). Paredes et al[116] demonstrated that an FCP threshold of 100 µg/g effectively predicted IUS activity with moderate sensitivity (73%) and specificity (71.4%), while Fang et al[117] highlighted the added utility of combining IUS scores (e.g., IBUS-SAS) with ESR and CRP, achieving high diagnostic accuracy (AUC: 0.912). Another study described highest accuracy with FCP cut off 150 µg/g (AUC: 0.756)[118]. In a retrospective study (n = 213 CD in clinical remission), leucine-rich alpha-2 glycoprotein (LRG) emerged as a superior biomarker compared to CRP for predicting active inflammation detected on IUS. An LRG threshold above 14.6 µg/mL was significantly associated with active sonographic findings, highlighting its potential role in identifying subclinical disease activity[[119]. Yzet et al[120] further refined these findings, showing that both FCP (< 92.9 µg/g) and BWT (< 3 mm) predicted mucosal healing (MH) with high specificity (89%) and PPV (96%). These studies underscore the synergy between IUS parameters with biomarkers to predict disease activity, MH, and treatment outcomes. Additionally, the study by Prentice et al[121] emphasized the potential role of FCP in complementing IUS findings, even in challenging scenarios like pregnancy.
Table 8 Summary of studies evaluating correlation intestinal ultrasound and fecal calprotectin.
FCP < 92.9 µg/g and BWT < 3 mm had high predictive values for mucosal healing (PPV: 96%, specificity: 89%, sensitivity: 77%)
IUS and TH: TH has emerged as a significant therapeutic target in CD and is increasingly recognized for its association with improved long-term outcomes such as reduced relapse rates, steroid-free remission, and lower surgical requirements (Table 9)[122,123]. Studies have shown that TH, achievable in 25%-38% of patients treated with biologics, outperforms MH as a prognostic indicator of disease control[124-126]. TH have been shown to predict relapse/steroid/treatment escalation free survival[122,127]. IUS has proven to be a reliable, non-invasive tool for assessing TH, with parameters like BWT and the IBUS-SAS serving as strong predictors. Post-induction BWT < 4.5 mm and IBUS-SAS < 25 are key thresholds for achieving TH, highlighting IUS’s utility in routine clinical practice and its potential to replace more invasive or costly methods such as endoscopy and cross-sectional imaging[126].
Table 9 Summary of studies evaluating transmural healing in Crohn’s disease with intestinal ultrasound.
Simplified TH: Normal BWT, no CDS; Extended TH: Normal BWT + 2 of 3 (normal CDS, no loss of stratification, no inflammatory fat); Complete TH: Normal BWT + all 3
TH at week 12 associated with clinical remission and no escalation of therapy at 52 weeks
Normal BWT, no hypervascularization, no inflammatory fat, no loss of stratification
TH predicted steroid-free clinical remission, lower need for drug escalation, and hospitalization; TH showed better predictive value than mucosal healing
Parietal healing: Normal BWT, no hyperemia, and absence of complications
PH associated with better outcomes, including relapse-free survival and reduced disease activity
A post-hoc analysis of prospective studies evaluating CD applied three distinct criteria for defining TH. One of these, termed transmural response (TR), was defined as a ≥25% reduction in BWT or normalization of BWT. Using this definition, TR was observed in 66% of patients, indicating a substantial rate of structural improvement with therapy. Based on various definitions, TH was achieved in 24%-37% of CD. TH at 12 weeks were more likely to achieve clinical remission with no change in therapy at week 52[123]. In prospective study of 77 CD patients, TH was shown to be better predictor of long term outcomes than MH with poor correlation between the two (Table 9)[128].
Predicting surgery in CD by IUS: Prediction of surgery in CD based on IUS parameters was primarily based on presence of CD complications (stricture, fistula and abscess) and other IUS parameters (wall echogenicity and thickness). One such score is US score = (2.5 X US pattern) + (1.5 X Bowel thickness) + (3 X Presence of fistulae/ abscesses) + (1.5 X Presence of stenoses). This score based on case control study of 147 CD patients (49 operated, rest non-operated) could predict surgery with 84% accuracy[129]. Earlier study (2004) evaluating only BWT showed BWT > 7 mm predicted risk of surgery in CD[130]. A small retrospective case-control study (n = 24 stricturing CD) showed that risk of surgery was predicted by presence of fistula, abscess and doppler activity[131]. In a recent prospective study of 225 ileal and /or colonic CD, IUS score, CD complications, FCP and male sex predicted 1 year disease course[63].
In pediatric age group, BWT, loss of mural stratification and fibrofatty proliferation on IUS predicted risk of surgery in a study of 42 subjects (22 operated)[132].
Correlation of IUS with other modalities
IUS correlation with colonoscopy: Multiple cross-sectional studies have assessed the relationship between IUS and colonoscopy in patients with CD (see Table 10)[133,134]. Among the various sonographic parameters, BWT demonstrated the most consistent and reliable correlation with endoscopic findings, reinforcing its value as a key marker for disease activity on IUS[133].
Table 10 Summary of studies evaluating correlation of endoscopy and intestinal ultrasound.
IUS sensitivity 67%, specificity 97% foe endoscopically active disease. Highest sensitivity (100%) ans specificity (95%) in transverse colon
IUS correlation with cross sectional imaging: The comparison of IUS with MRE and other cross-sectional imaging modalities for the evaluation of CD reveals complementary strengths and specific use cases. IUS has demonstrated superior sensitivity for detecting terminal ileum (TI) lesions compared to MRE, as shown in multiple studies, while MRE is more sensitive for upstream small bowel disease and overall disease extent (Table 11)[68,135-137]. This highlights the utility of IUS for localized disease monitoring and MRE for broader disease evaluation[138].
Table 11 Summary of studies comparing intestinal ultrasound and magnetic resonance enterography or computed tomography enterography.
MRE identified jejunal lesions not detected in high resolution ultrasound (n = 2). False positive MRE findings in proximal to mid ileum (n = 1). 100% sensitivity and specificity of MRE in terminal ileum
Localisation, bowel wall flow, active disease, structure, fistula and abscess
MRE and colonoscopy
IUS highly specific (> 85%), sensitive (> 85%), accurate (about 90%) with high negative predictive value (> 85%) except for stricture (75% sensitivity). Excellent positive predictive value except for CD complications Concordance in CD management in about 80%
Agreement for presence of Small bowel disease (MRI): 82% (new diagnosis). 81% (relapsing cohort). Colonic disease 64% (new diagnosis) 78% (relapsing cohort)
Terminal ileum thickness and mesenteric fat proliferation are useful to build a stepwise regression model which can predict MARIA score in terminal ileum on MRE
IBUS-SAS cutoff ≥ 46.7 predicted active disease (AUC = 0.86); MRE more sensitive for small bowel disease, IUS better for terminal ileum lesions
The studies emphasize the correlation between IUS and MRE findings for parameters such as BWT, vascularity, strictures and stratification. BWT and fat proliferation in the TI have been shown to predict the MARIA score using a stepwise regression model[139]. MRE demonstrated higher sensitivity and specificity for detecting the presence and extent of small bowel disease in a multi-center study and was superior in identifying jejunal lesions, which are often missed by IUS[140]. Additionally, MRE outperformed IUS in assessing strictures and loss of bowel wall stratification[141,142].
Ahmad et al[143] reported a strong correlation (r = 0.83) for bowel wall enhancement, confirming IUS as a reliable tool for disease activity assessment. Similarly, Dillman et al[144] found moderate to substantial agreement between IUS and MRE for BWT and complications like abscesses and strictures in pediatric CD. Hakim et al[54] further highlighted the efficacy of SICUS, which showed substantial agreement with MRE for detecting strictures (κ = 0.77) and lesions (κ = 0.63) in children, outperforming traditional TAUS.
MRE remains superior for evaluating complications such as strictures, loss of stratification, and jejunal lesions not detected by IUS, as demonstrated by Maccioni et al[145] and Taylor et al[1]. Despite this, IUS has been shown to provide comparable accuracy to CT enteroclysis for small bowel strictures and complications in studies by Onali et al[146] and Bhatnagar et al[147], offering a non-invasive, radiation-free alternative.
Emerging modalities like CEUS have demonstrated high correlation with MRE for assessing vascularity and thickness (Malagò et al[47]; Pauls et al[46]). CEUS and SICUS provide cost-effective and radiation-free imaging options, particularly valuable for young patients and those requiring frequent monitoring. In a retrospective study comparing CTE and SICUS (n = 59), IUS could identify lesions and complications in CD with high accuracy as compared to CTE. Similar results were seen in another study (n = 52) comparing CEUS and CTE[148,149]. The sensitivity of IUS was lower compared to CT for suspected early small bowel disease, whereas it was similar for established disease[150]. Recent findings by Statie et al[151] showed that the Limberg score on IUS had a sensitivity of 93.33% for active disease, while MRE correlated better with biomarkers like FCP, reinforcing its role in comprehensive disease evaluation.
For small bowel CD, Xu et al[68] validated the IBUS-SAS scoring system, which showed strong predictive accuracy for active disease (AUC = 0.86), comparable to MRE. However, colonic disease assessment revealed equivalency between IUS, CTE, and MRE, highlighting the modality-dependent variations based on disease location[68].
IUS correlation with small bowel capsule endoscopy: This has been evaluated in a prospective, single center study in which 50 patients with suspected CD with negative ileo-colonoscopy underwent both IUS and small bowel capsule endoscopy (SBCE). The diagnostic yield was 38% in both groups with significant correlation between IUS and SBCE findings. The diagnosis of CD was not fully established at 1 year follow up in cases where there was discordant results between IUS and SBCE[152]. Another study including known/suspected CD (n = 43) showed that IUS and SBCE had similar lesion detection rates (51% and 46% respectively)[153]. A recent study by Haissou et al[154] further demonstrated a strong correlation (r = 0.82, P < 0.001) between IUS (using SUS-CD) and SBCE (Lewis score) in small bowel CD. IUS showed a diagnostic accuracy of 79.7%, with high sensitivity (93.6%) and specificity (81.8%) for active disease. These findings highlight IUS as a reliable, non-invasive alternative to SBCE, particularly for monitoring small bowel CD, while acknowledging occasional discordance that may require combined or sequential use.
IUS correlation with small bowel enteroclysis: Studies in first decade of 21st century tried to evaluate correlation between US and small bowel enteroclysis (X ray). It was recognized that IUS can obviate the need for repeated radiographic examinations first in prospective blind study (n = 30 CD, 27 controls)[22]. The use of TAUS enhanced with a non-absorbable anechoic solution (PEG) showed a sensitivity of 72% and specificity of 100% in detecting small bowel disease, compared to enteroclysis. A prospective study on 296 CD patients showed that IUS could accurately identify extent of ileal disease detected intra-operatively or on enteroclysis (r = 0.52)[155]. A combination of small bowel enteroclysis and IUS known as ultrasound-enteroclysis (2000 mL of negative contrast infused at 120 mL/hour) could improve the detection of CD complications better than either modality alone as shown in a study of 246 patients[156]. However barium enteroclysis are seldom performed nowadays.
IUS in special populations
IUS in pediatric population: IUS is increasingly recognized as a valuable tool in the assessment and management of pediatric IBD, with studies consistently demonstrating its utility in evaluating disease location, severity, and response to therapy (Table 12). An earlier study in pediatric IBD and controls have shown that IUS was highly accurate in assessing location, endoscopic (77% sensitivity, 83% specificity) and histologic severity (75% sensitivity and 82% specificity) of disease[157]. IUS seems to be very useful in pediatric patients given that MRE may be difficult to perform in children due to confined space and difficulty to remain still. There is growing literature on role of IUS in children (Table 5).
Table 12 Summary of studies on intestinal ultrasound in pediatric inflammatory bowel disease.
MRE identified jejunal lesions not detected in HRUS (n = 2), False positive MRE findings in proximal to mid ileum (n = 1) 100% sensitivity and specificity of MRE in terminal ileum
2 weeks, 1 month, 3 months and 6 months on infliximab
BWT, length of bowel involved, bowel and mesenteric colour doppler signal changes as early as 2 weeks of infliximab therapy. Storing correlation between CDS intensity and fecal calprotectin
CEUS sensitivity 78.57%, specificity 100%. Concordance with endoscopy was substantial (κ = 0.62)
Multiple studies have shown that IUS has good correlation with MRE on the location and severity of disease[158,159]. The normal wall thickness in pediatric age group is less than 2 mm based on a study in non-IBD controls (n = 58)[160]. The accuracy of 1.9 mm cut off was 0.743 (AUC) (sensitivity: 64%, specificity 76%)[161]. The correlation was better in TI with both MRE and ileo-colonoscopy whereas jejunal lesions are can be better identified on MRE. False positivity was one of the drawbacks of MRE[145].
Recent advancements in IUS have extended its application to therapy monitoring and prognosis. Studies have demonstrated that IUS can track early response to infliximab, with changes in BWT and hyperemia observed as early as two weeks post-induction[112,132,162]. Dolinger et al[163] highlighted that a ≥ 18% reduction in BWT at week 8 predicted endoscopic remission with an area under the receiver operating characteristic (AUROC) of 0.99[163]. Additionally, Doppler signal intensity correlates well with FCP levels, providing an indirect measure of mucosal inflammation[162].
Various IUS scores for pediatric UC and CD have been described which needs external validation. In CD, pediatric CD ultrasound score has good sensitivity and specificity in both TI and colon. It was based on BWT in TI and BWT and mesenteric fat in colon[164]. Simple Pediatric Activity Ultrasound Score based on BWT, hyperaemia and inflammatory fat has been shown to predict active disease (score > 7, AUC: 0.82) in both UC and CD[165].
Okuhira et al[162] demonstrated that SBWT and mesenteric lymph node size (MLNS) on IUS correlated significantly with Lewis scores from SBCE (r = 0.52 and r = 0.45, respectively)[166]. Ponorac et al[48] further highlighted the utility of CEUS, reporting a sensitivity of 78.57% and specificity of 100% compared to SES-CD endoscopic scores. Similarly, Pallotta et al[55] validated small intestine contrast ultrasonography (SICUS) as a highly sensitive and specific tool for detecting CD lesions and complications.
IUS in post operative settings: The role of IUS in postoperative CD has been comprehensively evaluated in multiple studies, emphasizing its utility as a non-invasive alternative to ileocolonoscopy (Table 13). In a prospective study (Parente et al[167]) with a median follow up of 41 months after conservative surgery (stricturoplasty or minimal resection without macroscopically negative margin), BWT > 6 mm at 12 months after surgery was associated with 6 fold higher hazard of CD recurrence. Similarly, long segment thickening and unchanged wall thickness post surgery on IUS predicted surgical recurrence in a prospective study (n = 85)[168].
Table 13 Summary of studies evaluating role of intestinal ultrasound in post-operative Crohn’s disease.
BWT after surgery was unchanged or worsened in 43.3% of patients. Patients with unchanged/worsened BWT had a higher risk of clinical and surgical recurrence compared with those with normalized/improved BWT
Sonographic Score 2 (BWT > 5 mm or contrast enhancement > 46%) showed sensitivity (98%), specificity (100%), and accuracy (98.3%) for detecting endoscopic recurrence. Sonographic Score 3 was effective in identifying severe recurrence
Significant association between endoscopic recurrence and BWT/colour Doppler signal intensity. BWT > 3.4 mm had sensitivity (100%) and specificity (86%)
BWT ≥ 3 mm plus FCP > 50 μg/g identified 75% of patients with endoscopic recurrence (false positives 5%). Presence of mesenteric lymph nodes identified 56% of endoscopic recurrence
Incremental risks with increasing BWT were also highlighted by Cammarota et al[169], where BWT beyond 3 mm was linked to a 13% reoperation risk, escalating to 40% for BWT above 6 mm. Additionally, Yebra Carmona et al[170] reported significant associations between endoscopic recurrence and both BWT and CDS intensity. Specifically, a BWT cutoff of > 3.4 mm achieved 100% sensitivity and 86% specificity (AUC: 0.93). In a retrospective study (2015), positive power doppler signal in pre-anastomotic ileum on IUS performed 7-16 months after surgery along with wall thickness > 6 mm predicted 55.6% risk of surgical recurrence[171]. A cross sectional study showed that the diagnostic accuracy of IUS was superior to inflammatory markers (CRP, FCP) and clinical parameters[172].
Paredes et al[45] extended these findings by incorporating CEUS, which enhanced sensitivity and specificity in assessing postoperative recurrence. Rispo et al[173] conducted a meta-analysis suggesting a BWT cutoff of ≥ 5.5 mm for predicting severe postoperative recurrence (Rutgeerts ≥ 3), with pooled sensitivity of 83.8% and specificity of 97.7%.
In a recent prospective, multicenter study from Italy, IUS and colonoscopy were performed within one year of surgery. The combination of BWT ≥ 3 mm and FCP > 50 µg/g was able to detect 75% of patients with endoscopic recurrence, with a false positive rate of just 5%. Additionally, the presence of mesenteric lymph nodes on IUS was associated with endoscopic recurrence in 56% of cases (see Table 13)[5]. These findings support the utility of IUS in postoperative settings; however, larger prospective studies across diverse populations are necessary to validate these observations and to refine diagnostic cutoffs for improved predictive performance.
IUS in pregnancy: IUS offers a safe, non-invasive, and radiation-free modality for disease monitoring in pregnant individuals with IBD. A prospective cohort study involving 38 pregnant women (22 with CD and 16 with UC) demonstrated that while IUS is generally feasible during pregnancy, its utility decreases notably in the third trimester due to interference from the gravid uterus. Visualization rates declined particularly for the sigmoid colon (from 96% to 69%) and TI (from 91% to 22%). Despite this, IUS activity showed strong correlations with both clinical indices (r = 0.60) and FCP levels (r = 0.73). The modality achieved a sensitivity of 84% and specificity of 98% in identifying active disease, and was also effective in monitoring treatment response, with 80% sensitivity and 92% specificity[174]. In the largest prospective study to date in pregnant CD patients (82 patients, 91 pregnancies), two third of the symptomatic patients (8/12) had inactive disease on ultrasound which prevented escalation of therapy. On the other hand, active disease on IUS (n = 7) resulted in escalation of therapy or adverse outcomes when escalation was denied (1 miscarriage and 2 active disease 1 year postpartum)[175]. A case series have shown that FCP and IUS can help detect inflammatory pouch complications in pregnancy after ileal pouch anal anastomosis[176].
Role of IUS in IBD management during coronavirus disease 2019 pandemic: During the coronavirus disease 2019 pandemic, when access to endoscopic procedures was severely restricted, bedside IUS emerged as a valuable diagnostic tool. In a prospective observational study, the use of IUS led to changes in clinical management in up to 80% of patients presenting with acute symptoms or suspected IBD[177]. These findings underscore the utility of IUS in facilitating timely decision-making and optimizing patient care while alleviating pressure on overwhelmed acute care and endoscopy services.
Trans-perineal and transvaginal USG: Transperineal ultrasound (TPUS) has emerged as a valuable imaging tool for the assessment and monitoring of perianal fistulas in CD. Its non-invasive nature, accessibility, and real-time imaging capabilities make it a practical alternative or complement to more invasive techniques like examination under anesthesia (EUA) and endoscopic ultrasound (EUS) (Table 14).
Table 14 Role of trans-perineal ultrasound in Crohn’s disease.
Fistula detection and classification, abscess detection
TPUS demonstrated strong correlation with MRI in detecting perianal fistulas, offering a non-invasive, patient-friendly approach for fistula detection with high diagnostic accuracy. TPUS was effective in identifying superficial and intersphincteric tracts, complementing MRI for complex disease
TPUS showed excellent concordance with MRI and EUA for detecting superficial abscesses and fistulas, providing real-time visualization. While MRI excelled in deep-seated abscesses, TPUS was invaluable in mapping superficial tracts and guiding management
Fistula detection and classification, abscess detection
TPUS demonstrated diagnostic accuracy comparable to MRI in detecting fistulas and abscesses. Its real-time imaging capability made it a suitable alternative in cases where MRI was contraindicated or unavailable
Fistula detection and classification, abscess detection and classification
TPUS effectively identified internal openings and perianal abscesses, particularly in superficial fistulas. Its ease of use and non-invasive nature highlighted its utility in outpatient settings and as a complement to TRUS
Fistula detection and classification, abscess detection and classification
TPUS demonstrated utility in identifying perianal fistulas and abscesses, though MRI provided additional details for complex and deep-seated lesions. TPUS was particularly effective in identifying inflammation and monitoring post-treatment changes
Fistula detection and classification, internal opening and abscess detection
TPUS was a valuable tool for detecting superficial fistulas and internal openings. Its real-time imaging capability complemented EUA by providing an additional, less invasive option for follow-up assessments
Studies have consistently highlighted TPUS’s diagnostic accuracy in detecting fistulas and associated complications. Terracciano et al[178] demonstrated a strong correlation between TPUS and MRI findings, particularly in identifying superficial and intersphincteric fistulas, with high sensitivity and specificity. Similarly, Maconi et al[179] reported that TPUS was comparable to MRI in classifying fistula types and detecting abscesses, underscoring its utility in preoperative assessment. In an earlier study, Maconi et al[180] showed that TPUS effectively identified internal openings and superficial abscesses, further supporting its role in outpatient and follow-up settings.
TPUS has also been shown to complement MRI and EUA in complex cases. Mallouhi et al[181] demonstrated that TPUS, when used alongside MRI, enhanced the detection of superficial abscesses and fistulas while providing real-time visualization of inflammation and response to treatment. Stewart et al[182] highlighted TPUS’s role in detecting internal openings and monitoring healing, especially in patients unable to undergo invasive procedures like EUA.
While MRI remains the gold standard for visualizing complex fistulas and deep-seated abscesses, TPUS offers a cost-effective, patient-friendly option for longitudinal monitoring. Its ability to track inflammatory changes, healing status, and early recurrence makes it particularly valuable for follow-up in CD patients[183].
In conclusion, TPUS is a reliable, non-invasive modality for fistula monitoring in CD. It complements MRI and EUA, particularly in superficial and intersphincteric fistulas, and provides a practical alternative for patients who may not tolerate invasive procedures. Further studies are warranted to standardize its use and integrate it into routine clinical practice for CD management.
The usefulness of trans-vaginal sonography (TVS) have been described for non-gynaecological indications such as evaluation of rectal/perianal CD complications as a complementary modality to trans-abdominal USG[184]. A recent study (Pal et al[185]) highlighted TVS as a complementary modality, demonstrating that rectal wall thickness > 5 mm and modified Limberg’s vascularity scores ≥ 1 strongly correlate with active rectal disease (AUC = 0.968 and 1.0, respectively). TVS offers superior rectal imaging in parous women, addressing limitations of TPUS and TAS. Both TPUS and TVS provide non-invasive, radiation-free options for monitoring rectal disease, complementing TAS and cross-sectional imaging.
Gastroenterologist led IUS
Emerging evidence supports the feasibility and accuracy of IUS when performed by gastroenterologists, even with limited training. A pilot study demonstrated that clinicians trained with approximately 200 supervised scans could reliably assess disease activity, extent, and complications, showing good concordance with both MRE (n = 42) and colonoscopy (n = 38)[186]. Similarly, healthcare professionals trained through a structured IUS curriculum achieved diagnostic accuracy comparable to radiologists, with AUC values ranging from 0.71 to 0.81 versus 0.67 to 0.79, respectively[187]. In a feasibility analysis of 79 patients with either suspected or known IBD, IUS demonstrated high sensitivity for detecting key pathological features—bowel wall thickening (90%), strictures (94%), and masses (75%)—when compared to reference imaging or endoscopy performed within a three-month window[188]. Even in low-volume or non-specialist centers, IUS has shown strong diagnostic performance, with reported sensitivity and specificity for identifying active inflammation reaching 88% and 93%, respectively[189]. Despite these promising results, the widespread implementation of gastroenterologist-performed IUS faces significant hurdles. These include limited access to hands-on training, institutional preferences for other imaging modalities, insufficient administrative support, increased clinical workload, and resistance from radiology departments. A UK-based survey found that while enthusiasm for IUS was high, 70% of respondents felt inadequately trained or lacked confidence in performing the examination independently[190].
IOA with IUS: Consistency among operators is essential for the widespread adoption of IUS. A prospective study evaluating IOA found the highest concordance for measurement of terminal ileal wall thickness, with excellent agreement for Bowel Wall Thickness [Interclass coefficient (ICC): 0.882], followed by mesenteric echogenicity (0.841), wall stratification (0.685), vascularity (0.681), and lymph node assessment (0.633)[191]. Another study involving blinded expert reviewers reported an overall IUS score agreement (kappa) of 0.749[18].
In pediatric populations, IOA has also been explored. In one study involving both radiologists and gastroenterologists performing IUS in children with suspected or confirmed IBD, the kappa values for detecting disease activity were 0.58 in the TI, 0.49 in the transverse colon, and 0.52 in the descending colon[187]. Dillman et al[192] found good agreement for BWT (ICC: 0.67) and detection of strictures (κ = 0.54–0.68), with near-perfect agreement for identifying abscesses (κ = 0.92–1.00). However, Doppler signal intensity showed only moderate reproducibility (ICC: 0.48–0.58), indicating variability in assessing vascularity.
A prospective analysis that separated newly diagnosed (n = 11) from relapsing CD (n = 27) reported substantial agreement for small bowel involvement in both groups (κ = 0.64 for new, κ = 0.63 for relapsed cases). In contrast, colonic disease showed fair agreement in new diagnoses (κ = 0.27) and moderate agreement in relapsing disease (κ = 0.56)[147].
In summary, IOA is generally substantial for core IUS parameters, particularly for BWT. However, agreement varies depending on the bowel segment assessed and tends to be higher in established disease compared to new diagnoses, especially for colonic involvement.
Point of care IUS and clinical decision making: Point-of-care IUS (POCUS) has emerged as a valuable tool in guiding real-time clinical decisions in IBD care. Multiple studies have demonstrated that POCUS influences treatment strategies in approximately 40%–60% of cases (see Table 15)[18,20,193]. One of the key advantages of IUS is its ability to detect active inflammation even in patients who are clinically asymptomatic, thereby prompting timely therapeutic interventions. The resulting management decisions include both escalation and de-escalation of treatment, as well as referrals for surgical evaluation when necessary. In terms of diagnostic performance, POCUS has shown moderate to good agreement with both MRE and ileo-colonoscopy. It correlates well with these modalities in assessing the presence, distribution, and complications of disease in both CD and UC (see Table 15)[20,186]. Evidence from a retrospective cohort study in the United States (n = 148) further supports the role of IUS in treatment monitoring. In that study, therapeutic decisions guided by IUS were validated by follow-up outcomes, demonstrating effective inflammation control in both active and remission-phase patients[194]. Additionally, a prospective study involving 117 patients (89 with UC and 28 with CD) found that increased BWT and heightened CDS intensity were independent predictors of immediate treatment intensification. Moreover, the presence of bowel wall stratification loss alongside elevated BWT predicted the need for subsequent therapeutic adjustments[195]. St-Pierre et al[196] reinforced the clinical value of POCUS by showing that it identified active disease in 65% of 158 IBD patients. This led to medication changes in 57% of cases and enabled the deferral or avoidance of urgent endoscopic procedures in 85%, thereby optimizing care while minimizing procedural burden.
Table 15 Summary of studies evaluating role of point of care ultrasound in inflammatory bowel disease.
POCUS changed management (escalation, de-escalation, surgery referral) in nearly 60% of cases. Half of the patients with clinically inactive disease had IUS activity
Compared to MRE, POCUS was accurate in assessing disease activity, extent, and complications. POCUS had moderate agreement with MRE (κ = 0.50) and ileo-colonoscopy (κ = 0.55)
POCUS changed management in 40% of cases. Accuracy of decision improved from 63% to 90%. Surgical decisions were taken in 11% of cases. Colonoscopy and POCUS assessments were comparable
POCUS changed management in 60% of cases, leading to a 48% change in medications. Correlation with IUS was 86.3%, and correlation with MRI was 80%. Adoption of IUS reduced the reliance on MRI
POCUS detected active inflammation in 65% of cases, leading to changes in IBD-specific medications in 57%. Avoided or delayed urgent endoscopy in 85%, significantly improving resource utilization and reducing procedural burden
IUS and artificial intelligence or machine learning: A recent study trained a convolutional neural network (CNN) in 1008 images (805 training, 203 for classification 50% with abnormal BWT) to help assist inexperienced operators distinguish normal from thickened bowel in CD. The machine learning (ML) module had an accuracy of 90% (AUC = 0.98) with sensitivity and specificity of 86% and 94% respectively. In the absence of widespread training, AI may help by assisting in automatic detection of bowel inflammation and standardization of image interpretation[2].
Recent advancements in artificial intelligence (AI) and ML are revolutionizing the application of IUS in IBD. A recent study by Zhou et al[70] introduced novel scoring models combining bowel ultrasound parameters and biomarkers for predicting CD activity, achieving excellent predictive performance for both mucosal and transmural disease states (AUC: 0.927 and 0.851, respectively). Jing et al[197] established a regression model using multimodal ultrasound (including B-mode, color Doppler, contrast-enhanced, and SWE), integrating seven key ultrasound parameters to predict CDAI with high accuracy (R² = 0.72).
A recent study trained a CNN in 1008 images (805 training, 203 for classification 50% with abnormal BWT) to help assist inexperienced operators distinguish normal from thickened bowel in CD. The ML module had an accuracy of 90% (AUC = 0.98) with sensitivity and specificity of 86% and 94% respectively. In the absence of widespread training, AI may help by assisting in automatic detection of bowel inflammation and standardization of image interpretation[2]. Moreover, Gu et al[198] demonstrated the use of radiomics in bowel ultrasound, employing CNN to automate detection of bowel wall abnormalities. This model using XGBoost achieved 93.8% sensitivity/specificity, 93.7% accuracy and AUC of 0.98. Such AI-powered innovations in IUS hold significant promise for improving diagnostic accuracy, reducing operator dependency, and enabling real-time disease monitoring and therapeutic optimization in IBD.
These developments highlight the potential of AI-integrated IUS as a transformative tool for precision medicine in IBD management, reducing reliance on invasive modalities like ileocolonoscopy and enhancing patient-centered care. Further validation through multicenter studies is necessary to confirm their utility in routine clinical practice.
Utility of IUS
Patient acceptability: IUS stands out for its exceptional patient acceptability. In comparative assessments, acceptance rates for IUS reached 99%, significantly higher than those for MRE (88%) and colonoscopy (60%). Notably, patients indicated that while comfort was valued, diagnostic accuracy remained their top priority[199]. In a separate multinational study involving 37 individuals, participants expressed a clear preference for noninvasive approaches such as IUS. However, they remained open to undergoing invasive procedures like colonoscopy when clinically necessary. The study also highlighted the importance of involving patients in shared decision-making processes[200]. Among pediatric populations, both children and their caregivers favored IUS due to its noninvasive nature and its role in enhancing their understanding of the disease[201].
Cost effectiveness: While IUS is generally regarded as a cost-efficient tool for disease monitoring, comprehensive economic evaluations remain limited. A study conducted in the United Kingdom suggested that integrating IUS into clinical practice could potentially reduce the need for MRE by up to 55% and colonoscopy/sigmoidoscopy by 28%. The only clinically relevant findings that might be missed included two cases of colonic polyps detected by colonoscopy and minor upper gastrointestinal or extra-intestinal findings seen on MRE—none of which significantly altered patient management. The estimated cost savings from such an approach were approximately £500000 annually[202]. In a separate decision analysis model, strategies involving IUS for the initial assessment of suspected CD were found to be the most economical, regardless of whether the pre-test probability of disease was low or high[10]. However, it's important to note that cost structures and reimbursement policies vary widely across different healthcare systems, which may influence the generalizability of these findings.
Survey on widespread adoption of IUS: Evidence from multiple surveys and observational studies indicates a growing trend in the adoption of IUS, although its integration into routine clinical practice remains variable and somewhat limited. In the United Kingdom, a 2014 survey revealed that only 44% of radiology departments utilized IUS, and primarily for younger patients under 40 years old with a low clinical suspicion of CD[203]. An Italian analysis found that 24% of all ultrasound referrals involved bowel-related evaluations, with a balanced distribution between suspected and confirmed gastrointestinal conditions[204]. More recent UK data indicate that around 30% of centers now offer IUS services, in contrast to universal access to MRI. Notably, IUS had a shorter average wait time for reporting (1–4 weeks) compared to MRI (4–6 weeks)[205]. A qualitative study involving 14 key stakeholders explored both the perceived advantages and barriers to implementing IUS services, offering valuable insights into the practical considerations surrounding its adoption[206]. Patient perspectives have also been explored; in an Australian survey of 121 individuals with IBD, IUS emerged as the preferred method for disease monitoring, and was linked with improved disease-specific knowledge[207]. Supporting this trend, a retrospective cohort study from the Netherlands demonstrated a steady increase in POCUS use for IBD over time, coinciding with a decline in MRI utilization for similar purposes[20].
Utility of IUS as prescreening tool in clinical trials: Dolinger et al[208] highlighted the role of IUS as an effective pre-screening tool in IBD and CD clinical trials. The findings revealed that segmental BWT ≥ 3.6 mm, showed high accuracy (AUROC: 0.95) for detecting moderate-to-severe colonic inflammation in the colon, with 89% sensitivity and 93% specificity. IUS parameters strongly correlated with the SES-CD score, highlighting its potential to reduce unnecessary colonoscopies and improve trial efficiency. This work underscores the utility of IUS in clinical trial settings, enabling non-invasive and accurate disease assessment.
DISCUSSION
The systematic scoping review underscores the critical role of IUS in the diagnosis, monitoring, and management of CD. IUS offers a non-invasive, real-time, and radiation-free imaging modality that is increasingly being recognized for its utility across various stages of CD. However, certain limitations and gaps in evidence remain, highlighting the need for further validation and standardization.
IUS is a reliable tool for detecting inflammation in suspected CD, with high sensitivity for the TI and left colon. Its diagnostic performance, with sensitivity ranging from 65–85% and specificity from 80%–98%, positions it as a valuable adjunct to endoscopic and cross-sectional imaging. However, its sensitivity for lesions in the duodenum, jejunum, and rectum remains low due to anatomical challenges[3,7]. Recent advancements, such as SICUS and TPUS, have improved its ability to evaluate the small bowel and rectum, respectively. These findings highlight the growing utility of IUS in the initial diagnostic workup of suspected IBD.
IUS has limited evidence in distinguishing CD from mimics like BD and intestinal tuberculosis[12]. More studies are warranted evaluating the role of IUS in differentiating IBD from its mimics. The existing findings from available studies need to be validated further.
IUS excels in detecting subclinical inflammation, making it a valuable tool for monitoring disease activity and predicting preclinical relapse[195]. Similar to UC, scoring criteria in CD is based on BWT and CDS along with bowel wall stratification and mesenteric fat[64]. Although several such scoring systems have been developed for CD, only few are validated (e.g. IBUS-SAS) for treatment response and outcome prediction[66].
Elastography can help differentiate fibrotic from inflammatory strictures and predict biologic response as well as risk of surgery although elastography is not widely utilized and standardized[78]. CEUS is a reliable, non-invasive, and versatile imaging modality in CD, complementing traditional techniques like MRI and endoscopy while offering unique advantages in real-time assessment and radiation-free monitoring. CEUS, when combined with elastography, can provide a comprehensive evaluation of transmural and microvascular disease activity, guiding both medical and surgical decision-making.
IUS demonstrates high diagnostic accuracy for complications of CD, such as strictures, fistulas, and abscesses. Studies have reported sensitivities of 78%–90% and specificities of 90%–99% for detecting these complications[89]. Advanced modalities like CEUS have enhanced its ability to distinguish inflammatory abscesses from phlegmons, aiding surgical decision-making.
IUS correlate well with ileo-colonoscopy and fecal biomarkers as shown in several studies except for the fact that IUS can not evaluate rectum well. Trans-perineal ultrasound could help visualize the rectum and help in perianal fistula monitoring. Combining IUS and biomarkers to improve disease monitoring, reduce reliance on invasive procedures, and guide therapeutic decision-making in clinical practice.
IUS is also helpful in evaluating TH as an optional target in “treat to target” strategy similar to histologic healing in UC[123]. TH has been associated with better long-term outcomes, including reduced relapse rates and surgery requirements. By facilitating early and accurate monitoring, IUS aligns with treat-to-target strategies and supports deeper remission endpoints, significantly enhancing CD management.
MRE may score over IUS on the presence and extent of small bowel disease. MRE and Endoscopy may have an edge over IUS in evaluation of jejunal and upper gastrointestinal involvement. Overall, the findings support the integration of IUS into routine practice as a reliable, non-invasive tool for monitoring localized CD, especially in the TI. MRE retains its role as the gold standard for comprehensive disease evaluation and assessing complications. The complementary use of these modalities ensures optimal diagnostic accuracy while balancing patient safety and cost considerations.
The utility of IUS in special situations have been summarized. IUS is very useful tool for pediatric IBD given that MRE may be difficult to perform in children. The dynamic nature of IUS is another advantage over MRE which provides static image. Although jejunal lesions could be better identified on MRE, false positive results are not uncommon. IUS has shown promise in predicting therapeutic response to biologics and assessing the risk of surgical intervention in patients with IBD. However, while its utility extends to pediatric populations, current IUS scoring systems require further validation in children, particularly with the development of age-adjusted reference values.
IUS with FCP can predict endoscopic recurrence a 1 year in three-fourth of post-operative CD with high accuracy. Further prospective research should focus on predictors of early post-operative recurrence[5]. Despite promising results, further multicenter prospective studies are needed to refine its role in postoperative settings. The radiation free, non-invasive nature of IUS is particularly helpful in pregnancy although gravid uterus can hinder evaluation of sigmoid colon and TI in third trimester[174].
POCUS performed by gastroenterologists has shown diagnostic accuracy comparable to that of radiologists after limited training. However obstacles include the limited availability of structured training programs, concerns about increased workload, and resistance from radiology departments, often stemming from a protective stance over imaging-based diagnostics[190]. The IOA is acceptable for various ultrasound parameters (highest agreement for BWT). IOA was better for both for colonic and established disease (as compared to small bowel and newly diagnosed). POCUS can alter management of IBD in more than half of the lesions although more data is required to support “treat to target strategy” based on POCUS[18]. ML models and computer vision further augment the accuracy of IUS, particularly for novice operators, by standardizing image interpretation and automating the detection of bowel abnormalities[2]. The ability to integrate clinical knowledge with imaging findings positions gastroenterologists favorably for performing IUS in CD management.
IUS was the most preferred monitoring tool for IBD over MRE and colonoscopy. Although discomfort is an important factor choosing the modality for monitoring, patients emphasized that accuracy is more important that discomfort with patient involvement in shared decision making[198,199]. Both children with IBD and their parents preferred IUS over other modalities[200].
IUS is cost effective in the sense that it could avoid nearly half of MRE and one-fourth of colonoscopies[201]. However, more data is required. The billing and geographic differences in standard of care should be considered while interpreting cost-effectiveness studies. It is important to note that colonic polyps and upper gastrointestinal/extramural manifestations would be missed on IUS. Although IUS is being adopted increasingly, training and expansion of IUS services are warranted in several parts of the world[202].
Despite its advantages, IUS in CD requires further validation and standardization, particularly in advanced modalities like CEUS and elastography. While scoring systems such as IBUS-SAS have shown strong correlations with clinical and endoscopic indices, their integration into routine practice needs broader standardization. More prospective, multicenter studies are needed to confirm the utility of IUS-driven algorithms in improving clinical outcomes. Furthermore, the use of IUS in differentiating CD from its mimics remains underexplored, requiring robust comparative studies. We did not use any specific tool to assess bias or study quality. We did not assign levels of evidence or grades of recommendation, as this is a qualitative systematic review focused on synthesizing available literature rather than conducting a formal meta-analysis. Our aim was to provide a comprehensive overview of the clinical applications, advantages, and limitations of IUS in CD, rather than to establish graded recommendations.
CONCLUSION
IUS has emerged as an indispensable tool in the management of CD, with its applications spanning from initial diagnosis to monitoring therapeutic response and predicting complications. Its ability to provide real-time, radiation-free imaging makes it an attractive option for patients and clinicians alike. IUS can predict endoscopic response and even TH in CD. Stricture characterization by IUS elastography or contrast enhanced US lacks validation and standardization. IUS has demonstrated the ability to predict early treatment response to biologics and small molecules, with measurable changes observed as early as two weeks into therapy. Given its high diagnostic accuracy, IUS has the potential to serve as a noninvasive alternative to MRE and ileo-colonoscopy for routine monitoring. However, certain limitations remain—its sensitivity is reduced for detecting lesions in the upper gastrointestinal tract, jejunum, rectum, and for surveillance of colitis-associated neoplasia. Despite these limitations, IUS is particularly valuable in specific clinical scenarios, including use during pregnancy, in pediatric IBD, and in the postoperative monitoring of CD. IUS by trained gastroenterologists is as accurate as radiologists which can be improved further by automated detection of thickened bowel loops by use of AI. POCUS alters management in substantial number of patients although comparative studies with standard management for “treat to target” strategy is lacking. By addressing existing limitations and expanding its applications through further research and standardization, IUS has the potential to redefine the diagnostic and therapeutic landscape of CD.
Footnotes
Provenance and peer review: Invited article; Externally peer reviewed.
Peer-review model: Single blind
Specialty type: Medicine, research and experimental
Country of origin: India
Peer-review report’s classification
Scientific Quality: Grade A, Grade C, Grade C, Grade C, Grade D
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