Transabdominal intestinal ultrasound and its parameters used in the assessment of pediatric inflammatory bowel disease

Abstract

This article extends on the use of transabdominal intestinal ultrasound in diagnosing pediatric inflammatory bowel disease. Some of the more essential features used in assessing bowel inflammation, such as hyperemia and wall thickness on ultrasound, are expanded upon from the publication on imaging and endoscopic tools in pediatric inflammatory bowel disease.

Key Words: Inflammatory bowel disease; Intestinal ultrasound; Limberg score; Hyperemia; Bowel wall thickness

Core Tip: This letter to the editor discusses some of the most important parameters of intestinal ultrasound used in assessing inflammatory bowel disease in children.

TO THE EDITOR

I read with interest an important focused review by Hudson et al[1] that mentioned the use of intestinal ultrasound (IUS) and some of its characteristics in assessing pediatric inflammatory bowel disease (IBD). Items used to assess bowel inflammation on IUS include echostratification, motility, hyperemia, and bowel wall thickness (BWT)[1,2]. Of these, BWT and hyperemia are of the most significance.

BWT

BWT is considered the most important characteristic of IUS because bowel wall swelling indicates inflammation[3,4]. In healthy children, BWT ranges from approximately 0.8 mm to 1.9 mm in the small bowel and 1.0 mm to 1.9 mm in the colon, according to a pooled meta-analysis (Table 1)[5]. In children with IBD, cutoff values range from 2.5 mm to 3 mm; however, a consensus value is yet to be established by the scientific community[6]. Another study by Chiorean et al[7] revealed that children with Chron’s disease had an increased thickness of the ileocecal bowel wall (> 3 mm) compared to healthy age-matched controls. With these existing data, the optimal cutoff value may be defined at 2–2.5 mm.

Table 1 Mean bowel wall thickness modified from van Wassenaer et al[5].

Age in years	Jejunum	Ileum	Cecum	Ascending colon	Transverse colon	Descending colon
0–4	1.0 [0.4]	1.3 [0.2]	1.1 [0.2]	1.1 [0.2]	1.0 [0.2]	1.1 [0.2]
5–9	0.8 [0.1]	0.9 [0.1]	1.1 [0.1]	1.1 [0.2]	1.2 [0.2]	1.2 [0.2]
10–14	0.8 [0.1]	1.0 [0.2]	1.4 [0.2]	1.3 [0.3]	1.3 [0.2]	1.3 [0.2]
15–19	0.9 [0.1]	1.1 [0.1]	1.6 [0.2]	1.4 [0.2]	1.4 [0.2]	1.4 [0.2]

Data are mm [standard deviation].

For the most accurate value of BWT, it is recommended to begin measurement at the lumen-mucosa interface and stop at the hypo-hyperechoic interface between the muscularis propria and the serosa[8]. BWT should always be measured by IUS in clinical suspicion of IBD as it predicts the severity of disease activity by visualizing all five layers of the bowel wall[6,8,9]. It is important to note that despite the importance of BWT, it is not pathognomonic for IBD[7,8]. A large spectrum of other diseases, such as vascular, neoplastic, or infectious conditions, should also be considered. Physicians should use clinical correlation in conjunction with imaging findings to arrive at the correct diagnosis.

HYPEREMIA

Hyperemia is a sign of active disease in an inflamed intestine and is the second most common parameter used to evaluate bowel wall vascularity[9,10]. It is measured with Doppler sonography, which shows increased vascular signals in the submucosa that penetrate the muscularis propria in the clinical context of IBD[11,12]. An increased signal on Doppler predicts disease severity in both pediatric and adult populations[5,11,12].

Hyperemia can be scored semi-quantitatively or dichotomously using the modified Limberg score (Table 2), which measures vascularity[13,14]. This score differentiates four grades of hyperemia with an abnormal score of 2 or above[15]. Getting a Limberg value on IUS is recommended as it correlates well with endoscopic and histopathologic disease severity[16]. Given the semi-quantitative nature of the scoring system, there is a potential for inter-rater variability[17]. Additionally, Doppler sonography can be compromised by occasional tissue motion artifacts[18]. Due to the combination of these events, other advanced quantitative measurements have been proposed. It is recommended to set the color Doppler pulse repetition frequency to 5–7 cm/s to maximize the capture of flow in small vessels/capillaries with a set gain to remove motion artifacts[2]. Although there is no standard protocol for the measurement of color Doppler in children, it is important and should be measured given its ability to predict disease severity.

Table 2 Limberg classification of bowel wall vascularity in inflammatory bowel disease.

Grade	Description
0	Normal bowel wall with no thickening, well-delineated mural stratification, no color Doppler signal
1	Wall thickening (hypoechoic wall thickening and partially obscured mural stratification) and absent mural flow
2 (hypo-flow)	Wall thickening with intermittent (or spot) increases in vascularity
3 (hyper-flow)	Wall thickening with protracted regions of increased vascularity
4 (hyper-flow)	Color Doppler flow signals in both the bowel wall and surrounding mesenteric fat

CONCLUSION

IUS has revolutionized the way physicians assess and monitor pediatric IBD. It is less expensive and invasive than endoscopic procedures and is a valuable tool to evaluate disease activity, complications, and response to therapy. BWT and hyperemia are the two most important features used in assessing bowel inflammation on ultrasound. Emerging research in the field suggests comparable specificity and sensitivity regarding IUS and colonoscopy. Although more extensive prospective data are needed, IUS is expected to provide a shift away from invasive procedures used in the assessment and management of pediatric IBD.