Inflammatory bowel disease (IBD) encompasses a group of chronic inflammatory conditions of the gastrointestinal tract, primarily including Crohn’s disease and ulcerative colitis. The rate of patients affected by these conditions has been growing in the last decades, with an estimated 2.39 million Americans living with this diagnosis in 2020.¹ About 25% of those affected are children.² Active inflammation in the context of IBD increases the risk of disease complications, such as requiring surgery and developing colon cancer. However, symptoms have been shown to not accurately correlate to intestinal inflammation and ongoing bowel damage.^3,4 Therefore, the assessment of disease activity relies on invasive techniques, such as colonoscopy and cross-sectional imaging (ie, Computer Tomography Enterography and Magnetic Resonance Enterography), which are costly and laborious tests. Repeated imaging using these techniques is important to assess for the complete reversal of inflammation, termed mucosal healing, which was shown to lead to much better long-term outcomes.⁵

Intestinal ultrasound (IUS) has emerged as a valuable technique for screening patients with concerning symptoms of IBD and monitoring individuals with known disease. It has the advantages of being feasible at the bedside in the gastrointestinal clinic, noninvasive, painless, requiring no preparation from the patient, and not exposing the patient to ionizing radiation. IUS has been used for monitoring disease activity for many years in Europe and is now being rapidly adopted in the United States.

IUS Features of Intestinal Inflammation

IUS is generally performed using a high-frequency linear transducer to visualize the intestinal wall and surrounding structures in real-time and a curvilinear low-frequency transducer to assess for disease complications, often located in the pelvis. The thickness of the bowel wall, which comprises layers such as the mucosa, submucosa, and muscularis, measures under 3mm in healthy adults, but this measurement increases in the setting of inflammation.⁶ Bowel layers can be distinct or more disturbed depending on disease severity. Other important features include the presence of abnormal increased Doppler signals in and along the bowel wall, which are usually absent in healthy patients and progressively more prominent in diseased bowel. Furthermore, peri-intestinal fat can be increased in the presence of disease. Examples of these IUS features are illustrated in Figure 1.

Screening With IUS

One of the key advantages of IUS in IBD management is its ability to screen for the presence of disease in patients with nonspecific symptoms that could be due to IBD. By visualizing the thickness of the intestinal wall, the presence of bowel wall edema, and the extent of inflammation, ultrasound can help identify active disease and assess its severity. Indeed, a study demonstrated that IUS could distinguish between patients with Irritable Bowel Syndrome (IBS) or functional symptoms and patients with new or flaring IBD.^7,8 The use of IUS by trained providers can help with resource allocation and expedite invasive testing in the right patient without delays, and avoid unnecessary invasive investigation in patients who do not require it.

Monitoring Disease Progression and Treatment Response

In addition to screening, IUS can have a central role in monitoring response to treatment. Although there is a growing armamentarium of treatments for IBD, no single treatment has led to endoscopic remission rates higher than about 40–50%.⁹ Repeat ultrasound examinations can track changes in the thickness of the intestinal wall and complications over time. This real-time feedback allows for the timely optimization of treatment strategies, with subsequent improvement in patient outcomes. This proactive approach to objective evaluation of disease activity and continuous optimization of therapies, named the treat-to-target approach, has been demonstrated to improve long-term complication-free remission.^5,10 Moreover, ultrasound can detect complications such as strictures, abscesses, and fistulas, guiding treatment decisions and surgical planning.

Advantages of IUS

Several factors contribute to the growing popularity of IUS in IBD management:

1. Noninvasive: IUS does not require the insertion of instruments into the body, minimizing patient discomfort and reducing the risk of complications.
2. Radiation-free: Unlike CT scans, which involve ionizing radiation, ultrasound uses harmless sound waves, making it safe for repeated examinations by professionals, including in pregnant women and children.
3. Real-time imaging: IUS provides immediate feedback, allowing healthcare providers to assess disease activity and complications on the spot.
4. Cost-effective: Compared to other imaging modalities, IUS is relatively affordable, potentially increasing patient accessibility in various healthcare settings.

Conclusion

Intestinal ultrasound (IUS) has emerged as a valuable tool in the screening and monitoring of inflammatory bowel disease. Its noninvasive nature, lack of radiation exposure, real-time imaging capabilities, and cost-effectiveness make it an attractive option for healthcare providers and patients alike. By incorporating IUS into the diagnostic algorithm for IBD, clinicians can improve the accuracy of diagnosis, optimize treatment strategies, and enhance patient outcomes.

In the ever-evolving landscape of IBD management, IUS stands out as a versatile and effective imaging modality, offering valuable insights into disease activity and treatment response. As research continues to elucidate its utility and refine its techniques, IUS is poised to play an increasingly prominent role in the personalized care of individuals living with IBD.

References:

1. Lewis JD, Parlett LE, Jonsson Funk ML, et al. Incidence, prevalence, and racial and ethnic distribution of inflammatory bowel disease in the United States. Gastroenterology 2023 Nov; 165(5):1197–1205.e2. doi: 10.1053/j.gastro.2023.07.003. Epub 2023 Jul 20. PMID: 37481117; PMCID: PMC10592313.
2. Abraham BP, Mehta S, El-Serag HB. Natural history of pediatric-onset inflammatory bowel disease: a systematic review. J Clin Gastroenterol 2012; 46:581–589.
3. Modigliani R, Mary JY, Simon JF, et al. Clinical, biological, and endoscopic picture of attacks of Crohn’s disease. Evolution on prednisolone. Groupe d’Etude Thérapeutique des Affections Inflammatoires Digestives. Gastroenterology 1990; 98:811–818. doi: 10.1016/0016-5085(90)90002-i. PMID: 2179031.
4. Jharap B, Sandborn WJ, Reinisch W, et al. Randomised clinical study: discrepancies between patient-reported outcomes and endoscopic appearance in moderate to severe ulcerative colitis. Aliment Pharmacol Ther 2015; 42:1082–1092. doi: 10.1111/apt.13387
5. Ungaro RC, Yzet C, Bossuyt P, et al. Deep remission at 1 year prevents progression of early Crohn’s disease. Gastroenterology 2020 Jul; 159(1):139–147. doi: 10.1053/j.gastro.2020.03.039. Epub 2020 Mar 26. PMID: 32224129; PMCID: PMC7751802.
6. Novak KL, Nylund K, Maaser C, et al. Expert consensus on optimal acquisition and development of the international bowel ultrasound segmental activity score [IBUS-SAS]: a reliability and inter-rater variability study on intestinal ultrasonography in Crohn’s disease. J Crohns Colitis 2021; 15:609–616. doi: 10.1093/ecco-jcc/jjaa216. PMID: 33098642; PMCID: PMC8023841.
7. Novak KL, Jacob D, Kaplan GG, et al. Point of care ultrasound accurately distinguishes inflammatory from noninflammatory disease in patients presenting with abdominal pain and diarrhea. Can J Gastroenterol Hepatol 2016; 2016:4023065. doi: 10.1155/2016/4023065. Epub 2016 Apr 20. PMID: 27446838; PMCID: PMC4904691.
8. St-Pierre J, Delisle M, Kheirkhahrahimabadi H, et al. Bedside intestinal ultrasound performed in an inflammatory bowel disease urgent assessment clinic improves clinical decision-making and resource utilization. Crohns Colitis 360 2023 Sep 21; 5(4):otad050. doi: 10.1093/crocol/otad050. PMID: 37809033; PMCID: PMC10558199.
9. Cholapranee A, Hazlewood GS, Kaplan GG, Peyrin-Biroulet L, Ananthakrishnan AN. Systematic review with meta-analysis: comparative efficacy of biologics for induction and maintenance of mucosal healing in Crohn’s disease and ulcerative colitis controlled trials. Aliment Pharmacol Ther 2017 May; 45(10):1291–1302. doi: 10.1111/apt.14030. Epub 2017 Mar 22. PMID: 28326566; PMCID: PMC5395316.
10. Colombel JF, Panaccione R, Bossuyt P, et al. Effect of tight control management on Crohn’s disease (CALM): a multicentre, randomised, controlled phase 3 trial. Lancet 2017 Dec 23; 390(10114):2779–2789. doi: 10.1016/S0140-6736(17)32641-7. Epub 2017 Oct 31. Erratum in: Lancet 2018 Dec 23; 390(10114):2768. PMID: 29096949.

Mallory Chavannes, MD, MHSc, is an Assistant Professor of Pediatrics in the Division of Gastroenterology, Hepatology, & Nutrition, and is Medical Director of the Inflammatory Bowel Disease Program, at Children’s Hospital Los Angeles.