The Emerging Role of Ultrasonography in Ulcerative Colitis

Abstract

Background/Objectives: Intestinal ultrasound (IUS) is a non-invasive and reliable technique for the assessment and monitoring of ulcerative colitis (UC) in the era of tight disease control, although its accuracy is reduced for rectal evaluation. Its utility is further enhanced by transperineal ultrasonography (TPUS) and has also been demonstrated in patients with acute severe ulcerative colitis (ASUC) and in the postoperative assessment of ileal pouch function. Methods: We performed a narrative review on the emerging applications of IUS in UC with the findings obtained from research on the abovementioned topic on the PubMed database. Our search terms were “inflammatory bowel disease”, “IBD”, “ulcerative colitis”, “intestinal ultrasound”, “TPUS”, “HH”, “point of care ultrasound”, and “bowel ultrasound”. Results: IUS can assess UC disease activity and could be used in monitoring treatment response. Rectal assessment may represent a limitation of standard IUS, but the use of TPUS can overcome this issue, thus also allowing pouch evaluation after surgery. Another emerging application of IUS is in ASUC, a potential life-threatening condition where complete endoscopic assessment may not be feasible, so IUS could be a valid technique to assess disease extension and, in the first days, response to rescue therapy. Moreover, the use of hand-held sonography (HH), with portable ultrasonographic devices allowing point-of-care, bedside examination in various settings, is rising, showing accuracy comparable to standard techniques. Conclusions: IUS is emerging as a valuable tool in the management of patients with UC and could be an attractive option for point-of-care evaluation in the diagnosis, monitoring and prediction of long-term disease course, even after surgery or in the setting of ASUC. Complementary tools, such as TPUS and hand-held ultrasound, represent promising technologies, requiring prospective multicenter validation before routine clinical implementation.

1. Introduction

Ulcerative colitis (UC) is defined as a chronic, idiopathic, inflammatory disease characterized by continuous inflammation of the colonic wall starting from the rectum. In recent years, its incidence and prevalence have increased worldwide, resulting in areas with “acceleration in incidence” or “compounding prevalence” [1]. Thus, the need for an accessible and reliable way to perform inflammatory bowel disease (IBD) diagnosis and monitoring has become a priority to improve management and avoid expensive and time-consuming techniques.

The use of laboratory biomarkers, such as C-reactive protein (CRP) and fecal calprotectin (FC), together with clinical symptoms, does not accurately offer complete information about disease severity and extent [2]. IUS could be considered a valuable resource for suggesting or completing an IBD diagnosis and evaluating the disease course, even if endoscopy with biopsies remains mandatory [3,4,5]. IUS has gained increasing importance, being a cost-effective, reliable and non-invasive procedure for IBD evaluation, well tolerated by patients. Moreover, using IUS in a point-of-care setting (POCUS), such as completing a physical examination, can enhance IBD-related outcomes, thus ensuring an earlier diagnosis and prompt treatment initiation [6,7,8]. In this context, hand-held ultrasound (HH) devices represent a promising novelty, with the possibility to perform evaluation at the bedside, with accuracy comparable to conventional IUS [9].

Evaluation of the rectum using standard IUS can be difficult because of its deep location. In this context, transperineal ultrasound (TPUS) can help to better define rectal wall thickness and vascularity [10].

Several recent reviews and the updated ECCO-ESGAR-ESP-IBUS guidelines have addressed the role of IUS in IBD, including UC [11,12,13]. However, most of the existing literature has focused primarily on well-established parameters and validated activity scores. This review specifically aims to synthesize the current evidence on less consolidated, emerging applications of IUS in UC—namely, TPUS, ASUC monitoring, hand-held devices, artificial intelligence-assisted interpretation, and environmental sustainability—while critically distinguishing the strength of evidence supporting each application.

The aim of this review is to critically appraise the emerging role of IUS in the management of patients with UC, distinguishing well-established clinical applications from promising but still preliminary ones, with particular focus on TPUS, ASUC, HH and AI.

2. Methods

We performed a narrative review based on findings identified through a literature search on the emerging role of IUS in UC on the PubMed database. Our search terms were “inflammatory bowel disease”, “IBD”, “ulcerative colitis”, “intestinal ultrasound”, “TPUS”, “HH”, “point of care ultrasound”, “bowel ultrasound”. We combined these using the set operators AND or OR. We selected original articles, abstracts, systematic reviews and meta-analyses published in English. We excluded case series and case reports. Moreover, references to original articles and significant reviews were screened to find additional publications. All studies underwent initial screening through title and abstract evaluation. Unlike a systematic review, this narrative review provides a broad overview of this topic, which is less specific and potentially biased.

3. IUS in Evaluation of Disease Activity and Monitoring

Disease activity in UC can be evaluated through a number of ultrasonographic features. Of these, the two parameters relied upon most frequently are bowel wall thickness (BWT) and vascularization (Figure 1). A BWT ≥ 3 mm is regarded as pathological at the level of both the ileum and the colon [13,14]. To gauge vascularization, the color Doppler signal (CDS) is examined, most often by applying the Limberg score (LS) or its modified form (mLS) [15]. In order to make the assessment of UC activity more uniform, several scoring systems based on IUS have been proposed. The one adopted most widely, and the only one to undergo external validation, is the Milan Ultrasound Criteria (MUC); it derives from a straightforward equation combining BWT and CDS and correlates closely with endoscopic evaluation [16,17]. A MUC > 6.2 is correlated to a moderate-to-severe endoscopic inflammation with a sensitivity of 85% and a specificity of 94% [18].

Figure 1.

Transabdominal intestinal ultrasound: Increased bowel wall thickness and vascularization in sigmoid colon of a patient with ulcerative colitis.

Besides the MUC, other IUS-based scoring systems have been developed to standardize disease activity assessment in UC. The UC-Intestinal Ultrasound index (UC-IUS), proposed by Bots et al., combines BWT, CDS, haustration pattern and mesenteric fat wrapping into a 0-to-7 severity scale, with segment-specific BWT cut-offs of 2.1 mm, 3.2 mm and 3.9 mm to discriminate increasing degrees of endoscopic Mayo activity [19]. Unlike the binary MUC, the UC-IUS was designed to provide a more granular grading of activity, including detection of milder endoscopic inflammation. More recently, the International Bowel Ultrasound Segmental Activity Score (IBUS-SAS), originally developed and validated through an international expert consensus for Crohn’s disease [14], has also been applied to UC. In a cohort of 58 patients, IBUS-SAS strongly correlated with partial and endoscopic Mayo scores, the UC Endoscopic Index of Severity (UCEIS), the Nancy histologic index, CRP and fecal calprotectin; a cut-off of 15.9 predicted endoscopic activity with 100% sensitivity, 80.0% specificity, a positive predictive value of 94.7% and a negative predictive value of 100% [20]. A subsequent multicenter study similarly showed a strong correlation between IBUS-SAS and endoscopic activity in UC, comparable to that of MUC and UC-IUS, suggesting that IBUS-SAS could serve as a unifying reference score applicable to both Crohn’s disease and UC [18]. Overall, while the MUC remains the most extensively externally validated and widely adopted score for a binary discrimination between inactive and active disease, UC-IUS and IBUS-SAS offer a more comprehensive, multiparametric assessment—incorporating bowel wall stratification, haustral pattern and mesenteric fat alongside BWT and CDS—which may better capture the full spectrum of transmural inflammatory activity in UC and improve sensitivity for milder disease grades.

Beyond BWT and CDS, several additional sonographic parameters contribute to the overall assessment of disease activity in UC, although with a more limited and less standardized evidence base. Bowel wall stratification (BWS), the preservation of the normal five-layer echo-pattern of the intestinal wall, is a qualitative marker of mucosal integrity: its disruption reflects deeper mucosal injury, such as erosions or ulcerations, and complements the quantitative information provided by BWT [21]. Loss of the haustral pattern has also been associated with endoscopic disease activity and treatment response, and is included, together with BWT and CDS, among the parameters correlating with endoscopic outcomes in several UC-specific ultrasonographic indices [22]. Notably, the original MUC description incorporated a broader panel of features—including BWS, mesenteric fat proliferation and enlarged mesenteric lymph nodes—but only BWT and CDS were retained in the final validated formula, as these emerged as the strongest independent predictors of endoscopic activity on multivariate analysis [16,17]. Mesenteric fat proliferation and lymphadenopathy may still provide ancillary information, particularly in more extensive or longstanding disease, but their diagnostic weight in UC remains less well characterized than in CD, where transmural and mesenteric involvement is more pronounced [19]. Strictures and prestenotic dilation, conversely, are infrequent in UC given its typically non-transmural, non-stenosing behavior; when present, they more often raise concern for a fibrotic stricture related to longstanding colitis or an underlying neoplastic process rather than reflecting active inflammation, and their role as activity parameters in UC is therefore limited compared to CD [17]. Similarly, ascites is a nonspecific finding that may accompany severe or complicated colitis but has not been validated as an independent marker of luminal inflammatory activity [23]. Taken together, while BWT and, to a lesser extent, CDS remain the most reproducible and clinically actionable IUS parameters in UC, a comprehensive sonographic assessment—incorporating BWS, haustral pattern, mesenteric fat and lymph nodes—provides additional qualitative information that may refine disease characterization, whereas strictures, prestenotic dilation and ascites are more relevant to the identification of complications than to routine activity grading.

In addition, IUS offers the possibility to predict severity and complications in UC, including colectomy, making it an ideal procedure for personalized evaluation and tight monitoring (Table 1). Scores above 6.2 on the MUC have been linked to poorer clinical trajectories (HR 3.87; p < 0.001), including a heightened likelihood of surgery (p = 0.019) and of corticosteroid use (HR 7.20; p = 0.066) [24]. One prospective cohort reported that patients who went on to colectomy displayed markedly greater BWT (5.3 mm vs. 4.1 mm; p = 0.001) and higher MUC values (9.4 vs. 6.4; p = 0.001); among them, it was the MUC rather than the Mayo Endoscopic Score (MES) that emerged as the sole independent predictor of colectomy (HR 1.48; p < 0.001), with a cut-off of 7.7 producing an AUC of 83% [25]. Beyond prognosis, IUS is also central to tracking how UC responds to treatment. In the TRUST-UC study, patients who responded clinically by week 12 showed a more pronounced reduction in BWT than non-responders (among subjects whose BWT had normalized, 90.5% achieved a symptomatic response versus 9.5% who did not; p < 0.001). In parallel, FC levels above 250 μg/g were found in 84% of those with persistently thickened bowel wall, as opposed to only 16.4% of those whose BWT had returned to normal [26]. Along the same lines, Allocca et al., studying a group of 49 UC patients commencing biologic therapy, observed that IUS remission at the end of induction (i.e., a MUC score < 6.2 at week 12) was the only independent predictor of endoscopic improvement or remission over the long term (NPV of 78% for endoscopic improvement, defined as MES ≤ 1, and 96% for endoscopic remission, defined as MES = 0), which highlights the considerable prognostic weight of an early IUS response [27].

3.1. Emerging Role of TPUS in UC

Assessment of rectal disease using conventional IUS may be challenging because of the rectum’s deep location within the pelvis. A recent meta-analysis reported that the pooled sensitivity and specificity of standard IUS for detecting rectal activity were 74.5% (95% CI, 53.0–88.3%) and 69.5% (95% CI, 33.6–91.1%), respectively. These values were considerably lower than those observed for the remaining colorectal segments, where pooled sensitivity and specificity reached 86.4% (95% CI, 76.1–97.6%) and 88.3% (95% CI, 58.1–97.6%), respectively [10].

In this setting, TPUS has emerged as a valuable non-invasive alternative, especially for subjects with isolated proctitis. This technique requires thorough knowledge of pelvic–perineal anatomy and specialized training to guarantee consistent results. TPUS is performed with the patient in the left lateral decubitus position, with the linear probe placed on the perineum in the peri-anal region. The ultrasound assessment explores the rectum, internal and external anal sphincter, the bladder, the pubis symphysis, the prostate or the vagina. Like traditional IUS, BWT and CDS are the main features to be assessed (Figure 2).

Figure 2.

Transperineal ultrasound in ulcerative colitis: Transabdominal ultrasound showing rectal wall thickness with Doppler signal.

Sagami et al. demonstrated that TPUS exhibits stronger correlation with clinical, endoscopic and histological activity than traditional IUS [28].

In another work, the same authors demonstrated that TPUS is able to predict clinical remission to induction therapy at a very early disease phase. They performed clinical assessment, laboratory biomarkers (CRP and FC) and TPUS, at week 1 and 8 after induction. Improvements in BWT and bowel wall flow at week 1 were independent predictors of remission at week 8, while changes in biomarkers were not [29].

Due to its non-invasiveness, TPUS could be a valid tool in special settings, such as pregnancy and pediatric subjects. Tokushima et al. evaluated 87 children with UC and 44 subjects with non-IBD proctitis undergoing TPUS before endoscopy and showed that rectal wall thickening (RWT) and microvascular signal at wall circumference (MSWC) were independent predictors of UC endoscopic activity (OR, 119.3; 95% CI, 10.21–5646; p = 0.002; OR, 8.80; 95% CI, 2.10–75.3; p = 0.01) [30]. Likewise, Jimbo et al. investigated TPUS performance in assessing rectal inflammation compared to colonoscopy in pediatric patients. Their findings indicated that both an RWT exceeding 4.5 mm and the detection of rectal wall flow correlated with endoscopic activity [31]. As for pregnancy, an investigation carried out in a limited number of pregnant women failed to show any association between TPUS and clinical or biochemical measures of rectal disease activity [32].

Considering the interesting role of TPUS in this population, due to non-invasiveness that is mandatory in these patients, further studies are required to evaluate its role.

Another setting where TPUS can be a useful technique is the evaluation of ileal pouch–anal anastomosis (IPAA). Pouchoscopy with biopsy sampling allows researchers to study pouch activity with the possibility of grading it according to Pouchitis Disease Activity Index (PDAI) [33]. There are few data on ultrasound pouch examination. Ardalan and colleagues, in a prospective study, first evaluated the accuracy of IUS in pouch assessment [34]. They examined 42 UC subjects with IPAA. The patients underwent standard IUS and TPUS, with pouchoscopy as a reference standard. Pre-pouch ileum was accurately investigated with traditional IUS, which was also able to distinguish moderate-to-severe inflammation of pre-pouch ileum, detecting a cut-off of 3 mm for BWT to define severe inflammation with 70% and 84% of sensitivity and specificity. Moreover, TPUS performed a more accurate assessment of the body of the pouch and the rectal cuff, with the use of a micro-convex probe rather than a convex one (85/97% versus 78/25% of patients overall, respectively; p = 0.06). Overall, the study suggests the increased value of IUS in addition to FC detection in predicting endoscopic and histological active pouchitis, improving sensitivity to 93% and negative predictive value to 83%. This study could be a starting point to increase the interest of IUS and TPUS in pouch assessment, also highlighting the idea of transmural healing in these patients.

It should be noted that most of the evidence on TPUS in UC, including its role in predicting treatment response and in pouch assessment, derives from single-center studies with relatively small sample sizes (ranging from approximately 20 to 90 patients), and multicenter validation is still lacking before TPUS can be considered a standardized adjunct to conventional IUS.

3.2. Emerging Role of IUS in Acute Severe Ulcerative Colitis (ASUC)

ASUC is a potentially life-threatening disease requiring systemic steroids and, in refractory cases after 72 h, early rescue therapy with infliximab or ciclosporin to avoid worse outcomes (toxic megacolon/surgery) [35,36]. In this setting, IUS could be a useful tool for short-term disease monitoring and rapid clinical decision-making. In 2021, Smith et al., in a pilot study of 10 ASUC subjects, showed that IUS performed within 24 h after hospital admission may predict the need for rescue therapy. The authors demonstrated that any colonic segment with a wall thickness > 6 mm was a predictor of poor steroid response [37]. Ilvemark et al. used IUS in 69 patients with ASUC before corticosteroid treatment, after 48 ± 24 h and after 6 ± 1 day. They distinguished subjects in responders or non-responders after 7 days on the basis of clinical response or need for rescue therapy. There was no significant difference in baseline IUS, but after 2 days, underlying the early predictive role of IUS, a significant reduction in BWT was detected in responders compared to non-responders for both outcomes [38]. The same authors evaluated the follow-up of the same cohort of patients for 12 months to assess if IUS parameters could be useful in risk prediction of treatment failure or colectomy after one year. They showed that BWT < 3 mm 48 h after admission was associated with favorable outcomes, and no patients with BWT < 3 mm experienced colectomy during follow-up. Moreover, BWT ≥ 4 mm was associated with a shorter time before surgery [39]. In recent years, another class of drug was considered in patients with ASUC: JAK inhibitors. Although approved for moderate-to-severe UC, their specific use in ASUC is a rapidly evolving field. Some studies and case reports suggest that rapid-acting JAK inhibitors (such as tofacitinib or upadacitinib) may be considered as salvage therapy in patients with ASUC who fail steroid therapy, as an alternative or addition to biologics, due to their rapid onset of action [40,41]. IUS is now spreading in the evaluation of small molecules in the emergency setting; Gilmore et al. has used IUS to monitor a small cohort of six ASUC patients treated with upadacitinib [42]; four patients achieved steroid-free clinical remission by week 8, with disappearance of rectal bleeding and transmural healing assessed by IUS. It is worth emphasizing that this finding derives from a very small pilot cohort of six patients and should be regarded as hypothesis-generating rather than confirmatory; larger prospective studies are needed to establish the role of IUS in monitoring small-molecule therapy in ASUC.

Table 1.

Ultrasound predictors of outcomes in ulcerative colitis.

Ultrasound Parameter	Cut-Off	Predicted Outcome	Performance	Key Reference
BWT	≤3 mm (normalization)	Clinical response and lower FC levels	90.5% symptomatic response	[19]
BWT	>6 mm	Steroid failure in ASUC	Predictor of poor response	[30]
BWT (48 h after admission)	<3 mm	Favorable long-term outcome in ASUC	No colectomy during follow-up	[32]
BWT (48 h after admission)	≥4 mm	Increased colectomy risk in ASUC	Shorter time to surgery	[32]
MUC	>6.2	Moderate-to-severe endoscopic inflammation, adverse clinical outcomes, and increased risk of corticosteroid treatment and surgery	Sensitivity 85%, specificity 94%, HR 3.87; HR 7.30;	[16,17]
MUC	>7.7	High colectomy risk	AUC 0.83	[18]
MUC (<6.2 at week 12)	Remission threshold	Long-term endoscopic remission	NPV 96%	[20]
MUC	>7.8	Steroid resistance in pediatric ASUC	AUC 0.834	[36]
MUC	>8.7	Medical treatment failure in pediatric ASUC	AUC 0.878	[36]
RWT	>4.5 mm	Rectal endoscopic activity in pediatric UC	Significant association with active disease	[24]

Abbreviations: BWT, bowel wall thickness; MUC, Milan Ultrasound Criteria; RWT, rectal wall thickness; FC, fecal calprotectin; ASUC, acute severe ulcerative colitis; NPV, negative predictive value; AUC, area under the curve.

In a recent multicentric study, Scarallo et al. evaluated the role of IUS in evaluating short-term outcomes in 60 pediatric ASUC patients, a setting where it could be very important to use non-invasive tool for strict monitoring [43]. Non-responders had significantly higher wall thickness assessed in the left lower quadrant (6 vs. 4.2 mm; p < 0.001) and left upper quadrant (5 vs. 4 mm; p = 0.003) and had more frequent hypervascularity (Limberg’s score ≥ 3) evaluated in the same segments. Moreover, MUC > 7.8 (AUC = 0.834) was an optimal cut-off for predicting steroid resistance. At the second IUS evaluation, wall thickness > 4.8 mm and MUC > 8.7 in the left lower quadrant were associated with medical treatment failure (AUC = 0.844 and 0.878, respectively), while subjects in steroid-free clinical remission at week 8 had lower wall thickness (3.5 vs. 5 mm; p = 0.037) and MUC (5.3 vs. 8.7; p < 0.001).

3.3. Emerging Role of Hand-Held Ultrasound (HHIUS) in UC

Hand-held ultrasound (HH) devices represent a promising novelty, even if they need validation and improvement before routine clinical use. In cardiology and orthopedic settings it has become a new discipline called “echoscopy” [44,45,46], while data remain limited about the use of HH ultrasound in gastroenterology. Rispo et al. underlined the efficacy of hand-held intestinal ultrasound [HHIUS] in the diagnosis of CD [47]. In the HOCUS POCUS study, the same authors validated the use of portable ultrasound devices for managing patients with UC [9]. This work is very innovative because it shows that HHIUS, a readily available pocket-sized device (Figure 3), can assess activity and disease extent in UC, with accuracy comparable to conventional ultrasound and endoscopy. By evaluating the validated MUC, HHIUS demonstrated very high agreement with standard methods, showing that it could significantly simplify UC monitoring, thus permitting non-invasive and real-time assessment in a remote or point-of-care setting. In this context, remote monitoring through patient-performed scans represents a conceptually promising, though still highly preliminary, innovation [48]. This was the first reported case of a trained patient using a HH device to monitor his UC at home, in real time, during induction therapy. The patient was coached on using a pocket-size tool to visualize the sigmoid colon and measure bowel wall thickness. The subject subsequently performed the self-scans every day and transferred the images to the medical staff. In this way, HH ultrasound provided real-time information on treatment response and helped patients and their medical team to make more informed decisions about their therapies. However, this application is currently supported by a single reported case and should be regarded as an early proof-of-concept rather than a validated clinical practice; structured feasibility, training and safety studies in larger cohorts are required before patient-performed IUS can be considered for broader use.

Figure 3.

Hand-held intestinal ultrasound: Evaluation of ulcerative proctitis with increased rectal wall thickness and vascularization.

3.4. Emerging Technologies and Future Directions in IUS for UC

Artificial intelligence (AI) application in intestinal ultrasound has shown promising results in improving image interpretation and in automating measurements of bowel wall thickness, the evaluation of vascularity, and differentiating between inflammatory and fibrotic strictures, all critical features for personalized treatment choices [49].

In their interesting work, Gu et al. tested AI in IUS image interpretation with two models: a radiomic model and a Convolutional Neural Network. The radiomic model showed the best performance (AUC 0.98; 93.8% sensitivity and specificity) compared to the CNN (AUC 0.75), thus showing that radiomics can offer standardized and easily interpretable IUS analysis, reducing operator variability [50].

Further validation of these tools in prospective multicenter cohorts is needed to avoid intrinsic limits related to the low reproducibility of these models. In this context, we need further robust evidence in order to allow the spread of AI in IUS in clinical practice.

4. Discussion

In recent years, IUS has emerged as an important tool in point-of-care use in IBD during visits, together with clinical history, physical examination, and biomarkers, thus allowing direct decision-making and reducing the need for time-consuming, expensive and invasive procedures [51,52,53]. Performing IUS during visits avoids delays related to different procedure appointments and provides targeted and rapid patient management. IUS’s role is now recognized in the recent ECCO—ESGAR—ESP—IBUS guidelines, which incorporate IUS into algorithms for UC management [14,54], while TPUS, hand-held devices and AI-assisted interpretation are not yet formally incorporated into these recommendations and remain areas of active investigation. The consensus recommends IUS in the following clinical scenarios: early assessment (as an alternative to endoscopy for evaluating treatment response within 12 weeks), remission monitoring (combined with biomarkers and PROs to stratify the risk of relapse), symptomatic patients (as part of a multimodal diagnostic evaluation) and pouch complications (as a feasible diagnostic option alongside MR, TPUS, and CT). Recently, IUS has shown applicability in particular populations, such as children and pregnant women, where it offers a precise and harmless alternative for tight control when other procedures are less practicable or contraindicated [38,55]. Another condition which could benefit from this non-invasive procedure is ASUC, a life-threatening, emergency UC complication, that requires immediate hospitalization and prompt medical management. In subjects with ASUC, the absence of BWT has shown a specificity of 97% and a positive predictive value of 94.4% in predicting steroid failure in pediatric patients, thus allowing an early and non-invasive control [50]. In adult subjects, BWT > 4 mm within 24–48 h after systemic steroids predicted the need for rescue therapy or surgery (AUC up to 85%) [38]. Pregnancy represents the ideal setting for IUS performance in terms of non-invasiveness, particularly in the first trimester, with sensitivity and specificity up to 84% and 98%, respectively, for activity detection [56,57]. Table 2 summarizes current and emerging applications of IUS in UC. Regardless of its advantages, IUS may present some barriers that reduce widespread use: a lack of standardized protocols, limited training, various definitions of IUS remission and not widely used scores. Therefore, there is a need for protocol harmonization to increase and legitimize its clinical utility in practice.

Table 2.

Current and emerging applications of intestinal ultrasound in ulcerative colitis.

Clinical Setting	Technique	Main Parameters	Key Findings	Clinical Implication	Key References
Disease activity assessment	Standard IUS	BWT, CDS, and MUC	Strong correlation with endoscopic activity; MUC > 6.2 predicts moderate-to-severe inflammation	Non-invasive assessment of disease activity	[14,15,16]
Therapeutic response monitoring	Standard IUS	BWT and MUC	Early reduction in BWT and normalization of MUC predict clinical and endoscopic response	Early treatment optimization	[19,20]
Prognostic stratification	Standard IUS	BWT and MUC	High MUC associated with colectomy risk and adverse outcomes	Risk stratification and personalized follow-up	[17,18]
Rectal disease (proctitis)	TPUS	Rectal wall thickness and vascularity	Better assessment of rectal inflammation than standard IUS	Improved evaluation of isolated rectal disease	[10,21,22,23,24]
Acute severe UC (ASUC)	Standard IUS	BWT, CDS, and MUC	Early changes predict steroid response, rescue therapy, and colectomy risk	Rapid bedside monitoring and decision-making	[30,31,32,36]
Pregnancy	IUS/TPUS	BWT and vascularity	Safe and repeatable assessment without radiation	Monitoring when endoscopy is less feasible	[25,49,50]
Pediatric UC	IUS/TPUS	BWT, RWT, and vascularity	Accurate evaluation of disease activity and treatment response	Reduction in invasive procedures	[23,24,36,48]
Ileal pouch–anal anastomosis (IPAA)	IUS + TPUS	Pouch wall thickness and vascularity	Detection of pouch inflammation and rectal cuff disease	Complementary tool to pouchoscopy	[26,27]
Hand-held IUS	HHIUS	BWT and MUC	High agreement with conventional IUS and endoscopy	Bedside and outpatient evaluation	[6,7,9,44,45,46]

Abbreviations: IUS, intestinal ultrasound; TPUS, transperineal ultrasound; HHIUS, hand-held intestinal ultrasound; BWT, bowel wall thickness; CDS, color Doppler signal; MUC, Milan Ultrasound Criteria; RWT, rectal wall thickness; UC, ulcerative colitis; ASUC, acute severe ulcerative colitis; IPAA, ileal pouch–anal anastomosis.

Moreover, the emerging role of IUS in UC management is not only based on clinical and therapeutic aspects, but also on the good impact on environmental sustainability. The healthcare sector has a significant environmental impact, accounting for approximately 4–5% of global greenhouse gas emissions. Within diagnostic imaging, the choice of technologies and patient management methods plays a crucial role in reducing the carbon footprint [58]. IUS is evolving as one of the most sustainable diagnostic tools in gastroenterology: per-examination carbon footprint is estimated at 0.5–1.5 kg CO₂- equivalent, a lower amount than GI endoscopy, MRI or CT [59]. Unlike other procedures, IUS does not involve radiation or contrast agents, requires minimal energy, generates minimal waste (gloves or ultrasound gel) and minimizes patient travel due to its point-of-care use [60,61,62,63].

5. Conclusions

The traditional concept considering UC a mucosal disease and thus limiting cross-sectional imaging to CD has now been overcome. Recent data show that IUS is a valuable tool in UC too, accurately predicting endoscopic activity, even in a challenging setting such as ASUC, and monitoring patients and response to treatment. Standard IUS is ideal for sigmoid colon and colonic evaluation, while TPUS allows better assessment of rectum and ileal pouch–anal anastomosis. It appears particularly useful in pregnancy and pediatric settings, helping to reduce endoscopic examinations. Future research is focused on the evaluation of new applications, like HHIUS and AI models, in the era of real-time treat-to-target approaches, but data in these fields are still limited and prospective multicenter studies are needed before these technologies can be considered for widespread clinical implementation. There is a need for standardization and continuous training initiatives to promote full integration of these innovations into routine clinical practice.

Author Contributions

A.T.: Conceptualization, Methodology, Writing—Original Draft, and Writing—Review and Editing. L.B.: Data Curation and Writing—Review and Editing. A.R.: Data Curation and Writing—Review and Editing. A.D.G.: Data Curation and Writing—Review and Editing. O.M.N.: Data Curation and Writing—Review and Editing. F.I.: Data Curation and Writing—Review and Editing. F.P.: Writing—Review and Editing. M.P.: Writing—Review and Editing. F.D.: Writing—Review and Editing. F.C.: Supervision and Validation. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

Funding Statement

This research received no external funding.