Intestinal ultrasound for monitoring postoperative Crohn’s disease: A systematic review and clinical implications

Abstract

BACKGROUND

Postoperative recurrence is common in Crohn’s disease (CD), with endoscopic lesions in a majority of patients by 12 months after surgery. Ileocolonoscopy is the reference standard but is invasive and poorly suited to frequent surveillance. Intestinal ultrasound (IUS) - including small intestine contrast ultrasound and contrast enhanced ultrasound - is a repeatable, noninvasive alternative.

AIM

To summarize the evidence on the diagnostic accuracy and prognostic value of IUS for detecting postoperative recurrence in CD.

METHODS

We systematically searched PubMed and EMBASE through June 2025 for original English-language studies evaluating IUS against clinical or endoscopic outcomes in postoperative CD. This scoping review was conducted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guideline. After screening 259 unique records, 41 full texts were assessed and 20 studies were included.

RESULTS

Bowel wall thickness thresholds of ≥ 5 mm at the neo-terminal ileum predict endoscopic recurrence with sensitivities 81%-94% and specificities 86%-100%; lower cutoffs at the anastomosis (≥ 3-3.5 mm) also carry risk (data from singlecenter cohorts). Dualsite assessment (neo-terminal ileum + ileocolonic anastomosis) improves performance. Adding Doppler hyperemia or mesenteric lymphadenopathy increases accuracy; combining bowel wall thickness ≥ 3 mm with fecal calprotectin ≥ 50 μg/g yields high specificity (approximately 93%-100%) with a negative predictive value of nearly 95% when both are negative. Contrast enhanced ultrasound-based composite scores reach approximately 98% diagnostic accuracy in prospective cohorts. Small intestine contrast ultrasound shows similarly strong early diagnostic performance - for example, an area under the receiver operating characteristic curve up to 0.95 when using ileocolonic anastomosis wall thickness ≥ 3 mm to 3.5 mm plus lesion length, with 82%-94% sensitivity and > 90% specificity reported even within 7 days post-resection. Overall, IUS shows moderate agreement with endoscopy (κ approximately 0.5-0.8) and stronger prognostic value when performed within 12 months post-surgery.

CONCLUSION

IUS can be integrated into postoperative surveillance algorithms - particularly within the first year - and can reduce routine endoscopy in selected patients. Research priorities include standardized thresholds and composite scoring, consensus training/competency, and multicenter validation including artificial intelligenceassisted interpretation.

Key Words: Postoperative recurrence; Crohn’s disease; Bowel wall thickness; Small intestinal contrast ultrasound; Intestinal ultrasound

Core Tip: Intestinal ultrasound is a practical, non-invasive tool for monitoring postoperative Crohn’s disease. Bowel wall thickness > 3-5 mm, especially when persistent or worsening, predicts recurrence. Diagnostic accuracy improves with dual-site assessment (neo-terminal ileum and ileo-colonic anastomosis), Doppler hyperemia, and lymphadenopathy. Integration with fecal calprotectin enhances specificity and negative predictive value. Advanced techniques like contrast enhanced ultrasound and small intestine contrast ultrasound further refine detection. Early assessment within 12 months post-surgery is most prognostic. Intestinal ultrasound is well-suited for repeated follow-up, and when used systematically, may reduce reliance on routine ileocolonoscopy in selected postoperative patients.

INTRODUCTION

Postoperative recurrence (POR) remains a major clinical challenge in the long-term management of Crohn’s disease (CD), with endoscopic lesions developing in over 70% of patients within one year of ileocolonic resection[1]. While ileocolonoscopy is the current gold standard for detecting mucosal recurrence, it is invasive, costly, and not well tolerated for repeated use. From the patient’s perspective, repeated endoscopic procedures are associated with discomfort, risk, and diminished quality of life, underlining the need for less invasive tools. Intestinal ultrasound (IUS) is a real-time, radiation-free, patient-friendly modality that allows bedside assessment of transmural inflammation[2]. Despite multiple primary studies, no recent scoping or systematic review has specifically synthesized evidence on IUS for postoperative monitoring in CD based on emerging evidence, justifying the need for this review.

Over the past two decades, multiple studies have investigated the utility of IUS for detecting POR, with bowel wall thickness (BWT) emerging as a key sonographic marker. Enhancements such as Doppler vascularity, contrast enhanced ultrasound (CEUS), and small intestine contrast ultrasound (SICUS) have further expanded its potential[3,4]. However, current literature remains fragmented, with variability in timing, thresholds, definitions of recurrence, and operator expertise. There is no standardized algorithm integrating IUS into postoperative surveillance, and many clinicians remain uncertain about its comparative value vs fecal calprotectin (FCP) or cross-sectional imaging[5]. Additionally, questions persist regarding the optimal timing of IUS assessments and the predictive value of serial measurements or composite indices.

This systematic review aims to synthesize the literature on postoperative IUS in CD, with specific objectives to: (1) Summarize its diagnostic accuracy for recurrence detection; (2) Outline its prognostic value for clinical and surgical outcomes; and (3) Identify evidence gaps to guide future research. Unlike prior reviews, this synthesis integrates emerging evidence on CEUS, SICUS, and composite indices, thereby updating clinicians on the latest modalities.

MATERIALS AND METHODS

This scoping review was conducted to synthesize existing evidence on the use of IUS for detecting and monitoring POR in CD. A systematic search was performed in PubMed and EMBASE databases through June 30, 2025 using a structured strategy (“Crohn Disease” OR “Crohn’s disease”) AND (“Postoperative Complications” OR “post-surgical recurrence” OR “post-operative recurrence”) AND (“Ultrasonography” OR “ultrasonography” OR “bowel sonography”) OR (“Intestine, Small/diagnostic imaging” OR “small intestine contrast ultrasound” OR “SICUS”) OR (“contrast enhanced ultrasound” OR “CEUS”) (Figure 1). This scoping review was conducted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guideline. Only original research articles published in English were included; editorials, reviews, non-English publications, and conference abstracts were excluded. Two reviewers (Pal P, Kata P) independently screened titles/abstracts and full texts using a standardized form; disagreements were resolved by consensus with a third reviewer (Mateen MA). Although formal risk-of-bias tools were not applied given the scoping design, we qualitatively noted study limitations such as sample size, single-center design, and operator dependence.

Figure 1  Preferred Reporting Items for Systematic reviews and Meta-Analyses flow diagram illustrating the study selection process for this scoping review.

A total of 366 records were retrieved (81 from PubMed, 186 from EMBASE), and after removing 8 duplicates, 259 unique articles were screened. Following title/abstract review and full-text eligibility assessment, 41 articles were selected for detailed evaluation, and 20 met the inclusion criteria for final synthesis. We used a prespecified standardized extraction template (study design, setting, sample, timing post-operative, sonographic parameters and thresholds, reference standards, diagnostic/prognostic metrics, and integration with biomarkers/imaging).

RESULTS

IUS as a non-invasive predictor of POR in CD

BWT: The role of IUS in predicting POR in CD has steadily evolved through a series of landmark studies, each building on prior findings (Table 1). The earliest, Andreoli et al[6], demonstrated that BWT > 5 mm in the neo-terminal ileum (NTI) strongly predicted endoscopic recurrence, with 81% sensitivity and 86% specificity (overall diagnostic accuracy 83%). This established a foundational BWT threshold and showed that IUS findings correlated well with endoscopic outcomes, even when measured within weeks of colonoscopy. Subsequently, Parente et al[1] added longitudinal perspective by showing that persistent or increased BWT (≥ 6 mm or < 40% reduction from baseline) at 12 months post-surgery was associated with a markedly elevated risk of symptomatic recurrence [hazard ratio (HR) = 8.9]. This study emphasized the value of serial monitoring over time and introduced echo pattern abnormalities (e.g., hypoechoic or mixed patterns) as independent predictors of poor outcomes. Rispo et al[7] focused on early prediction, showing that BWT > 5 mm within just 12 months postoperatively predicted severe endoscopic recurrence (Rutgeerts ≥ i3) with 94% sensitivity and 100% specificity (Figure 2). This reinforced BWT as a surrogate for endoscopic severity and highlighted its potential to replace ileocolonoscopic in high-risk patients. Cammarota et al[8] expanded the evidence to a larger retrospective cohort, showing that even modest thickening (BWT > 3 mm at the anastomotic site) was associated with an increased risk of surgical recurrence (relative risk = 2.1). Importantly, this study explored graduated BWT thresholds (> 3 mm, > 4 mm, > 5 mm, > 6 mm), demonstrating that risk increased incrementally with wall thickness, thus offering a framework for risk stratification. Across prospective studies, sensitivity for detecting endoscopic recurrence ranged from 77% to 94%, while specificity consistently exceeded 85%.

Figure 2 Multimodal assessment of the ileo-colonic anastomosis in postoperative Crohn’s disease. A: Transabdominal ultrasound showing a thickened anastomotic site between the colon and ileum (marked with an asterisk) with gap in the submucosa; B: Measurement of bowel wall thickness (5.79 mm) proximal to the ileo-colonic anastomosis in neo-terminal ileum using high-frequency ultrasound; C: Ileocolonoscopic image showing ulcerated anastomotic site with suture material and few ulcers in neo-terminal ileum; D: Endoscopic view of the ulcerated anastomostic site with proximal ulcerations.

Table 1 Summary of key studies evaluating bowel wall thickness on intestinal ultrasound as a predictor of postoperative recurrence in Crohn’s disease.

Ref.	Year	Design	Number	Site assessed	Timing	BWT threshold	Outcome predicted	Sensitivity	Specificity	Statistic
Andreoli et al[6]	1998	Prospective	41	NTI	Within 2 weeks of colonoscopy	> 5 mm	Endoscopic recurrence	81%	86%	Accuracy = 83%
Parente et al[1]	2004	Prospective	127	NTI	12 months post-operative	≥ 6 mm or < 40% reduction	Clinical recurrence	NR	NR	HR = 8.9
Rispo et al[7]	2006	Prospective	45	NTI	12 months	> 5 mm	Endoscopic recurrence (Rutgeerts ≥ i3)	94%	100%	NR
Pallotta et al[10]	2010	Prospective	58 (111 evaluations)	Anastomosis + NTI	6-24 months post- operative	> 3.5 mm (ICA) + > 3 mm (NTI)	Endoscopic recurrence	100% (for ICA > 3.5 mm)	NR	AUROC = 0.95 (combined)
Cammarota et al[8]	2013	Retrospective	196	Anastomosis	6-15 months post- operative	> 3 mm	Surgical recurrence	NR	NR	RR = 2.1

NTI: Neo-terminal ileum; ICA: Ileocolonic anastomosis; BWT: Bowel wall thickness; NR: Not reported; HR: Hazard ratio; AUROC: Area under the receiver operating characteristic curve; RR: Relative risk.

Prognostic value of pre-operative and post-operative BWT monitoring by IUS in CD: Beyond its cross-sectional diagnostic role, BWT assessed via IUS also offers dynamic prognostic insights when tracked over time. In a prospective cohort, Maconi et al[9] evaluated both pre-operative and post-operative IUS findings in patients undergoing conservative surgery (strictureplasty or limited resection). They found that patients with unchanged or worsened BWT at 6 months postoperatively had significantly higher risks of both clinical recurrence (HR = 9.98) and surgical recurrence (HR = 16.15). Furthermore, a greater preoperative extent of bowel wall involvement - especially longer segments of thickened bowel - was also predictive of adverse outcomes. Several studies linked IUS findings with clinical outcomes, including reduced need for repeat endoscopy and lower rates of surgical recurrence when BWT regressed after surgery. These findings support the role of serial ultrasound monitoring in postoperative care and emphasize that not only absolute BWT thresholds but also the trajectory of BWT change can help stratify risk. Integrating early sonographic improvement into routine surveillance pathways may therefore help identify patients likely to benefit from intensified therapeutic interventions.

Dual-site assessment of BWT: While BWT at either the ileo-colonic anastomosis (ICA) or NTI independently predicts POR in CD, combining measurements from both sites significantly improves diagnostic accuracy. In a prospective cohort study, Pallotta et al[10] demonstrated that BWT > 3.5 mm at the ICA and > 3 mm at the NTI, when assessed together, yielded an area under the receiver operating characteristics curve of 0.95 for detecting endoscopic recurrence. This combined approach outperformed assessment at either site alone and supports the use of dual-site sonographic evaluation as a best practice in postoperative IUS.

Study heterogeneity: Across included cohorts, operator experience, probe frequency, machine vendors/settings, and BWT cut-offs (≥ 3-6 mm) varied, as did timing of assessment and reference standards (endoscopy vs mixed endpoints). These factors likely contributed to betweenstudy variability and should be addressed in future standardization efforts. All included studies were conducted in adult populations; pediatric cohorts were not represented.

Integrating additional IUS features in POR detection: Beyond BWT, several ultrasound and biomarker parameters offer incremental value in identifying POR of CD (Table 2). Furfaro et al[5] demonstrated that while BWT ≥ 3 mm alone is a modest predictor (accuracy 73%), adding mesenteric lymphadenopathy (odds ratio = 15.63) or (FCP ≥ 50 μg/g; odds ratio = 8.58) significantly improves diagnostic performance. The combination of BWT and FCP enhances specificity to 93%, and adding lymph nodes further eliminates false positives (100% specificity). Complementing this, Yebra Carmona et al[11] highlighted the role of hyperemia (grade ≥ 2 by color Doppler) as a key correlate of endoscopic recurrence and FCP levels. A dual-parameter approach of BWT > 3 mm plus hyperemia achieved a diagnostic accuracy of 83%, outperforming either parameter alone. These findings reinforce the use of composite IUS indices - including vascularity, lymph nodes, and BWT - in postoperative IBD care and suggest that when FCP is incorporated, non-invasive assessment may approach the reliability of ileocolonoscopy.

Table 2 Diagnostic performance of individual and combined intestinal ultrasound parameters and fecal calprotectin for detecting postoperative recurrence in Crohn’s disease, %.

Ref.	Year	Parameter	Sensitivity	Specificity	PPV	NPV	Diagnostic accuracy	Comment
Furfaro et al[5]	2023	BWT ≥ 3 mm	77	65	81	59	73	Independent predictor of POR; OR = 2.43
		Mesenteric lymph nodes	35	97	95	43	56	Strong predictor; OR = 15.63
		FCP ≥ 50 μg/g	83	64	81	67	76	Independent predictor; OR = 8.58
		BWT ≥ 3 mm + FCP ≥ 50 μg/g	65	93	94	59	75	Best combined predictor
		BWT ≥ 3 mm + FCP ≥ 50 μg/g + LN+	33	100	100	59	66	Highest specificity; no false positives
Yebra Carmona et al[11]	2022	BWT > 3 mm + hyperemia	81	87	85	84	83	Strong correlation with endoscopy and FCP
		Hyperemia alone (grade ≥ 2)	67	74	70	72	71	Associated with endoscopic recurrence and FCP

BWT: Bowel wall thickness; FCP: Fecal calprotectin; LN+: Mesenteric lymph node enlargement; PPV: Positive predictive value; NPV: Negative predictive value; POR: Postoperative recurrence; OR: Odds ratio.

Small intestinal contrast ultrasound in detecting POR

Multiple studies have consistently validated the role of SICUS in detecting POR in CD through evaluation of BWT and other sonographic features (Table 3). Onali et al[12] demonstrated that SICUS could identify POR in all patients across 1-3 years of follow-up, though correlation with moderate-to-severe endoscopic recurrence (Rutgeerts ≥ 2) was limited. In a robust multicenter study, Pallotta et al[10] showed that BWT > 3.5 mm at the ICA predicted all cases of endoscopic recurrence, and when combined with measurement of neo-terminal ileal lesion length, it achieved an excellent discriminatory value (AUROC: 0.95). Similarly, Calabrese et al[13] reported a diagnostic accuracy of 92.5% using a BWT threshold of 3 mm. Castiglione et al[14] further reinforced the early predictive potential of SICUS, demonstrating high sensitivity (82%-94%) and specificity (> 90%) for recurrence detection within just 7 days post-resection. Finally, Onali et al[15] emphasized the long-term utility of SICUS in monitoring postoperative CD recurrence, proposing its integration into routine surveillance alongside or even in place of ileocolonoscopy. Together, these studies affirm that BWT - particularly at the anastomotic site - offers a reliable, non-invasive metric for tracking postoperative disease recurrence, with enhanced predictive accuracy when combined with lesion length and clinical correlation.

Table 3 Summary of selected studies evaluating small intestine contrast ultrasonography in detecting postoperative recurrence in Crohn’s disease.

Ref.	Year	Design	Number	Timing of SICUS	BWT threshold	Sensitivity	Specificity	Accuracy/comments	Specificity	Statistic
Castiglione et al[14]	2008	Prospective	40	Within 7 days post-operative	> 3 mm	82%-94%	> 90%	Early detection with high sensitivity	NR	HR = 8.9
Calabrese et al[13]	2009	Prospective	40	Within 14 days post-operative	> 3 mm	92.5%	NR	Accurate grading of severity	NR	RR = 2.1
Onali et al[12]	2010	Prospective	58	12 months post-operative	> 3 mm	100%	NR	SICUS detected all cases of POR	100%	NR
Onali et al[15]	2016	Retrospective	58	3-year follow-up	> 3 mm	100%	NR	Useful long-term monitoring tool	86%	Accuracy = 83%
Biancone et al[3]	2007	Prospective	72	6-12 months post-operative	> 3 mm	NR	NR	Correlation with capsule endoscopy	NR	AUROC = 0.95 (combined)
Pallotta et al[10]	2010	Prospective	58	6-24 months post-operative	> 3.5 mm (ICA) + > 3 mm (NTI)	100%	NR	AUROC = 0.95 (combined ICA + NTI)	NR	NR

SICUS: Small intestine contrast ultrasonography; BWT: Bowel wall thickness; ICA: Ileocolonic anastomosis; NTI: Neo-terminal ileum; NR: Not reported; POR: Postoperative recurrence; AUROC: Area under the receiver operating characteristic curve; HR: Hazard ratio; RR: Relative risk.

CEUS in postoperative CD

CEUS has emerged as a powerful adjunct to conventional IUS in the postoperative setting of CD (Table 4). In a landmark prospective study, Paredes et al[16] demonstrated that CEUS significantly enhances the detection of both mild and severe endoscopic recurrence. Using parietal contrast enhancement thresholds (> 34.5% for any recurrence and > 70% for severe), the study showed that a sonographic score combining BWT > 5 mm or enhancement > 46% achieved a diagnostic accuracy of 98.3% (κ = 0.95). For identifying moderate-to-severe recurrence, a stricter composite score (BWT > 5 mm, CEUS > 70%, or presence of fistula) reached 94% sensitivity and an AUROC of 0.836. Importantly, CEUS also identified cases with normal wall thickness but abnormal enhancement, allowing early detection of recurrence. Supporting these findings, Martínez et al[4] emphasized CEUS’s utility in distinguishing inflammatory from fibrotic postoperative lesions and its additive value in comprehensive sonographic assessment. Together, these studies confirm CEUS as a reliable, non-invasive alternative to endoscopy, particularly when layered into structured sonographic scoring systems.

Table 4 Key studies evaluating the role of contrast enhanced ultrasound in the detection and characterization of postoperative recurrence in Crohn’s disease.

Ref.	Year	Technique	Sample size	Thresholds	Key findings
Paredes et al[16]	2013	CEUS	60	BWT > 3 mm; CEUS > 34.5%, CEUS > 46%, CEUS > 70%	CEUS improved diagnostic accuracy for endoscopic recurrence to 98.3% with score 2 (BWT > 5 mm or enhancement > 46%). Score 3 (BWT > 5 mm, enhancement > 70%, or fistula) detected 94% of severe recurrence. AUC = 0.99 for recurrence
Martínez et al[4]	2019	CEUS	N/A	N/A	CEUS effectively differentiated inflammatory vs fibrotic lesions post-surgery. Reinforced role of CEUS in enhancing IUS precision and in early recurrence assessment

CEUS: Contrast enhanced ultrasound; BWT: Bowel wall thickness; AUC: Area under the curve; IUS: Intestinal ultrasound; N/A: Not applicable.

Combined USE of IUS and leucocyte scintigraphy

In an innovative prospective study, Paredes et al[17] evaluated the combined performance of IUS and 99mTc-D,L-hexamethylene-propyleneamine oxime-labelled leucocyte scintigraphy (LLS) in detecting and grading POR in CD. Among 33 patients with available ileocolonoscopic data, both IUS and LLS demonstrated moderate standalone accuracy for identifying endoscopic recurrence (72.7% and 78.1%, respectively). However, when used in combination - defined as BWT > 5 mm and/or scintigraphy uptake grade 2 or grade 3 - the sensitivity and negative predictive value for diagnosing moderate-to-severe recurrence rose dramatically to 93.3% and 92.9%, respectively, with an overall accuracy of 81.8% and κ = 0.64. This synergistic approach outperformed either modality alone, especially in scenarios where colonoscopy was incomplete or declined. These findings suggest that combining IUS and LLS can provide a highly effective, non-invasive alternative for early detection and stratification of POR in CD.

Correlation between IUS and endoscopy

Two recent cross-sectional studies have explored the diagnostic agreement between IUS and endoscopy in the postoperative assessment of CD (Table 5). Yebra Carmona et al[11] assessed 39 patients and reported moderate concordance between IUS (defined by BWT > 3 mm and Limberg Doppler score > 1) and endoscopy (Rutgeerts ≥ i2), with κ = 0.5 and an AUROC of 0.75 - superior to both clinical scores and inflammatory markers. Building on this, Macedo et al[18] evaluated additional IUS features including bowel wall stratification and Doppler signal intensity. Their findings showed that loss of wall stratification and hyperemia were the most predictive parameters for endoscopic recurrence, with AUROCs of 0.88 and 0.85, respectively. BWT also remained a strong marker with an AUROC of 0.80 using a cut-off of 3.9 mm. These findings reinforce that when performed by trained operators, IUS can reliably reflect endoscopic recurrence and may guide surveillance strategies in place of or in addition to ileocolonoscopy.

Table 5 Comparison of diagnostic performance of intestinal ultrasound parameters with endoscopic findings (Rutgeerts score) in postoperative Crohn’s disease.

Ref.	Year	Sample size	IUS parameters	Reference standard	Agreement (κ)	AUROC	Sensitivity	Specificity	Key findings
Yebra Carmona et al[11]	2022	39	BWT > 3 mm + Limberg score > 1	Rutgeerts ≥ i2	0.5	0.75	81.0%	87.0%	IUS had higher diagnostic accuracy than clinical or lab parameters.
Macedo et al[18]	2022	39	BWT > 3 mm and/or Limberg score > 1	Rutgeerts ≥ i2	0.5	0.75	88.9%	61.9%	Loss of wall stratification and hyperemia were most predictive of recurrence.

IUS: Intestinal ultrasound; BWT: Bowel wall thickness; AUROC: Area under the receiver operating characteristic curve.

Comparative performance of FCP and IUS

FCP and IUS are increasingly recognized as complementary tools for early detection of postoperative CD recurrence (Table 6). In a pioneering prospective study, Orlando et al[19] compared FCP and IUS performance at 3 months post-surgery, with endoscopy at 12 months as the reference standard. While IUS showed high specificity (90%) but low sensitivity (26%) using a cut-off of BWT ≥ 5 mm, FCP at > 200 mg/L offered improved sensitivity (63%) but lower specificity (75%). This suggested that a high FCP in patients with a negative IUS could justify early colonoscopy. More recently, Furfaro et al[5] reported that both FCP ≥ 50 μg/g and IUS (BWT ≥ 3 mm) independently predicted recurrence, with sensitivities of 83% and 77%, respectively. The combination of FCP and IUS further enhanced specificity and positive predictive value, while the absence of both (FCP < 50 μg/g and BWT < 3 mm) yielded a negative predictive value of 95.5%. These findings support the integrated use of IUS and FCP to guide risk-based monitoring and potentially reduce the need for immediate endoscopy in low-risk postoperative patients.

Table 6 Summary of studies comparing fecal calprotectin and intestinal ultrasound for detecting postoperative recurrence in Crohn’s disease.

Ref.	Year	Sample size	Timepoint	FCP cut-off	IUS threshold	FCP sensitivity/specificity (%)	IUS sensitivity/specificity (%)	Key insight
Orlando et al[19]	2006	39	3 months (IUS, FCP), 12 months (endoscopy)	> 200 mg/L	BWT ≥ 5 mm	63/75	26/90	Calprotectin more sensitive; IUS more specific at 3 months. Combining both could guide early colonoscopy
Furfaro et al[5]	2023	> 100	3-6 months post-operative	≥ 50 μg/g	BWT ≥ 3 mm	83/64	77/65	FCP and IUS individually useful; combination improved specificity and PPV. FCP < 50 μg/g + BWT < 3 mm had NPV 95.5%

IUS: Intestinal ultrasound; FCP: Fecal calprotectin; BWT: Bowel wall thickness; NPV: Negative predictive value.

Timing matters: Early versus late IUS assessment post-surgery

The study by Piaz et al[20] provides compelling evidence that the prognostic accuracy of IUS and endoscopy in postoperative CD is highly dependent on timing. In this retrospective series of 201 patients followed for a median of 7.6 years, both endoscopic and sonographic recurrence - defined by BWT ≥ 4 mm or complications - were significantly predictive of clinical relapse when assessed within 12 months of ileocolonic resection. However, this predictive value was lost when assessments were performed after 36 months. Specifically, early IUS findings were independently associated with clinical and surgical outcomes, whereas late IUS assessments showed no significant prognostic relevance[20]. These findings underscore the importance of performing IUS within the first postoperative year to guide treatment decisions and support its role in the early risk stratification of recurrence.

DISCUSSION

This scoping review synthesizes the growing body of evidence supporting IUS as a valuable, non-invasive tool for the detection and monitoring of POR in CD. Across diverse clinical settings, IUS has demonstrated consistent correlation with endoscopic and clinical recurrence, with evolving techniques enhancing both sensitivity and specificity. Most included studies are singlecenter (prospective or retrospective) cohorts with modest sample sizes; a recent multicenter prospective study strengthens external validity of composite, noninvasive strategies combining IUS with FCP[5].

Evidence synthesis

BWT remains the cornerstone of sonographic evaluation, with thresholds ranging from 3 mm to 6 mm shown to predict clinical, endoscopic, and surgical recurrence[1,7,8]. Longitudinal studies reinforce that the trajectory of BWT - particularly failure to regress after surgery - is a strong prognostic marker. Incorporating serial assessments improves clinical decision-making by identifying patients at risk of early relapse. Further improvements in diagnostic accuracy are achieved by assessing both the NTI and the ICA, rather than relying on a single segment. Dual-site evaluation captures a broader spectrum of disease activity and, when combined with lesion length or enhancement, achieves near-perfect sensitivity in some studies[10].

Additional IUS features such as mesenteric lymphadenopathy, hyperemia, and wall stratification enhance the predictive power of BWT alone[5,11]. When paired with biomarkers like FCP, IUS offers a complementary and dynamic approach to non-invasive monitoring, improving both positive and negative predictive values. Notably, combining normal BWT and low FCP provides high confidence in excluding significant recurrence. Innovations such as SICUS and CEUS have further improved visualization and accuracy, particularly in patients with subtle disease or deep mural involvement[3,4,12,13,16]. CEUS, in particular, distinguishes inflammatory from fibrotic lesions, informing therapeutic choices in postoperative care. In specific scenarios, the combination of IUS with functional imaging modalities like LLS may provide additional value, particularly when colonoscopy is contraindicated or incomplete[17]. These multimodal strategies support individualized care without compromising diagnostic certainty. Finally, timing of assessment is critical. Studies consistently show that IUS has greatest prognostic value when performed within the first year following surgery. Late assessments (> 36 months) offer limited predictive utility, reinforcing the need for early incorporation of IUS into postoperative surveillance pathways[20].

Clinical implications

Based on the review, suggested surveillance algorithm (months 3-12 post-operative) is as follows (Figure 3). 3-6 months: IUS (NTI + ICA). If BWT < 3 mm and FCP < 50 μg/g - routine followup (negative predictive value approximately 95%). If BWT ≥ 3 mm or hyperemia/Lymph nodes - repeat IUS in 3 months ± optimize therapy; consider endoscopy based on symptoms/risk. 6-12 months: IUS ± CEUS/SICUS if equivocal. If BWT ≥ 5 mm (NTI) or ≥ 3-3.5 mm (ICA) and/or CEUS score positive - endoscopy to confirm and stage; escalate therapy. > 12 months: Continue risk-stratified IUS; reserve routine endoscopy for highrisk or discordant cases.

Figure 3 Suggested surveillance algorithm integrating intestinal ultrasound and fecal calprotectin for monitoring postoperative Crohn’s disease. BWT: Bowel wall thickness; FCP: Fecal calprotectin; NPV: Negative predictive value; IUS: Intestinal ultrasound; ICA: Ileocolonic anastomosis; CEUS: Contrast enhanced ultrasound; SICUS: Small intestine contrast ultrasound.

From a global perspective, while IUS is feasible and scalable in high-resource centers, low-resource settings may face barriers related to operator training and ultrasound infrastructure; however, its portability and low cost compared with endoscopy make it particularly attractive where access is limited.

Limitations

We limited inclusion to Englishlanguage, peer-reviewed original studies and did not include grey literature, which may introduce selection/publication bias. Considerable heterogeneity existed in operator training, equipment, thresholds, timing of assessments, and reference standards, limiting metaanalytic pooling. Consistent with scoping methodology, we did not perform a formal riskofbias assessment; findings should be interpreted as an evidence map to guide practice and research rather than as graded recommendation. Potential publication bias and the lack of formal cost-effectiveness analyses remain important caveats.

Research gaps

Despite this progress, key unmet needs include: (1) Prospective head-to-head studies comparing IUS, CEUS/SICUS, endoscopy, and crosssectional imaging; (2) Standardized thresholds and composite indices with external validation; (3) Operator training/competency frameworks; and (4) Evaluation of artificial intelligenceassisted, automated measurements to improve reproducibility and scalability.

Collectively, the reviewed evidence supports the integration of IUS into standard care for postoperative CD, not only as a surrogate for endoscopy in selected patients but also as a real-time, repeatable tool for personalized disease monitoring. While IUS can safely defer routine endoscopy in selected lowrisk patients, it should be viewed as complementary to ileocolonoscopy until standardized scoring and multicenter validation are established.

CONCLUSION

IUS is a robust, noninvasive option for postoperative surveillance in CD, especially within the first year after surgery. Its utility is amplified when assessments are performed early post-surgery, with studies confirming that IUS can complement or, in selected cases, substitute for endoscopic evaluation. IUS, particularly when combined with biomarkers such as FCP, should be incorporated into postoperative monitoring algorithms. Standardization and international validation are urgent priorities to transition IUS from promising research to routine practice.