How to perform gastrointestinal ultrasound: Anatomy and normal findings

Abstract

Gastrointestinal ultrasound is a practical, safe, cheap and reproducible diagnostic tool in inflammatory bowel disease gaining global prominence amongst clinicians. Understanding the embryological processes of the intestinal tract assists in the interpretation of abnormal sonographic findings. In general terms, the examination principally comprises interrogation of the colon, mesentery and small intestine using both lowfrequency and high-frequency probes. Interpretation of findings on GIUS includes assessment of bowel wall thickness, symmetry of this thickness, evidence of transmural changes, assessment of vascularity using Doppler imaging and assessment of other specific features including lymph nodes, mesentery and luminal motility. In addition to B-mode imaging, transperineal ultrasonography, elastography and contrast-enhanced ultrasonography are useful adjuncts. This supplement expands upon these features in more depth. © The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.

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World Journal of
Gastroenterology
World J Gastroenterol 2017 October 14; 23(38): 6923-7058
ISSN 1007-9327 (print)
ISSN 2219-2840 (online)
Published by Baishideng Publishing Group Inc

S
EDITORIAL
6923 Evolving role of FDG-PET/CT in prognostic evaluation of resectable gastric cancer
De Raffele E, Mirarchi M, Cuicchi D, Lecce F, Cola B
6927 Staging chronic pancreatitis with exocrine function tests: Are we better?
Sperti C, Moletta L
MINIREVIEWS
6931 How to perform gastrointestinal ultrasound: Anatomy and normal ndings
Atkinson NSS, Bryant RV, Dong Y, Maaser C, Kucharzik T, Maconi G, Asthana AK, Blaivas M, Goudie A, Gilja OH,
Nuernberg D, Schreiber-Dietrich D, Dietrich CF
6942 Dysphagia: Thinking outside the box
Philpott H, Garg M, Tomic D, Balasubramanian S, Sweis R
6952 Role of endoscopic ultrasound in idiopathic pancreatitis
Somani P, Sunkara T, Sharma M
ORIGINAL ARTICLE
Basic Study
6962 Delayed and short course of rapamycin prevents organ rejection after allogeneic liver transplantation in
rats
Hamdani S, Thiolat A, Naserian S, Grondin C, Moutereau S, Hulin A, Calderaro J, Grimbert P, Cohen JL, Azoulay D,
Pilon C
6973 Adipose-derived stromal cells resemble bone marrow stromal cells in hepatocyte differentiation potential
in vitro
and
in
vivo
Xu LJ, Wang SF, Wang DQ, Ma LJ, Chen Z, Chen QQ, Wang J, Yan L
6983 Fecal microbiota transplantation prevents hepatic encephalopathy in rats with carbon tetrachloride-
induced acute hepatic dysfunction
Wang WW, Zhang Y, Huang XB, You N, Zheng L, Li J
6995 Mitofusin-2 mediated mitochondrial Ca2+ uptake 1/2 induced liver injury in rat remote ischemic
perconditioning liver transplantation and alpha mouse liver-12 hypoxia cell line models
Liang RP, Jia JJ, Li JH, He N, Zhou YF, Jiang L, Bai T, Xie HY, Zhou L, Sun YL
Contents Weekly Volume 23 Number 38 October 14, 2017
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Contents World Journal of Gastroenterology
Volume 23 Number 38 October 14, 2017
7009 Expression of annexin II in gastric carcinoma and its role in gastric cancer metastasis
Han F, Shrestha S, Huang H, Lv HY, Nie C, Lin L, Lu ML
Retrospective Study
7016 Risk factors for postoperative recurrence after primary bowel resection in patients with Crohn’s disease
Yang KM, Yu CS, Lee JL, Kim CW, Yoon YS, Park IJ, Lim SB, Park SH, Ye BD, Yang SK, Kim JC
7025 Trends and outcomes of pancreaticoduodenectomy for periampullary tumors: A 25-year single-center
study of 1000 consecutive cases
EI Nakeeb A, Askar W, Atef E, Hanafy EE, Sultan AM, Salah T, Shehta A, Sorogy ME, Hamdy E, Hemly ME, El-Geidi AA,
Kandil T, El Shobari M, Allah TA, Fouad A, Zeid MA, El Eneen AA, El-Hak NG, El Ebidy G, Fathy O, Sultan A, Wahab MA
Prospective Study
7037 Testing for hepatitis B virus alone does not increase vaccine coverage in non-immunized persons
Boyd A, Bottero J, Carrat F, Gozlan J, Rougier H, Girard PM, Lacombe K
CASE REPORT
7047 Gastric adenocarcinoma of fundic gland type spreading to heterotopic gastric glands
Manabe S, Mukaisho K, Yasuoka T, Usui F, Matsuyama T, Hirata I, Boku Y, Takahashi S
7054 High-grade myobroblastic sarcoma in the liver: A case report
Wen J, Zhao W, Li C, Shen JY, Wen TF
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NAME OF JOURNAL
World Journal of Gastroenterology
ISSN
ISSN 1007-9327 (print)
ISSN 2219-2840 (online)
LAUNCH DATE
October 1, 1995
FREQUENCY
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EDITORS-IN-CHIEF
Damian Garcia-Olmo, MD, PhD, Doctor, Profes-
sor, Surgeon, Department of Surgery, Universidad
Autonoma de Madrid; Department of General Sur-
gery, Fundacion Jimenez Diaz University Hospital,
Madrid 28040, Spain
Stephen C Strom, PhD, Professor, Department of
Laboratory Medicine, Division of Pathology, Karo-
linska Institutet, Stockholm 141-86, Sweden
Andrzej S Tarnawski, MD, P hD, DSc (Med),
Professor of Medicine, Chief Gastroenterology, VA
Long Beach Health Care System, University of Cali-
fornia, Irvine, CA, 5901 E. Seventh Str., Long Beach,
CA 90822, United States
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World Journal of Gastroenterology (World J Gastroenterol, WJG, print ISSN 1007-9327, online
ISSN 2219-2840, DOI: 10.3748) is a peer-reviewed open access journal. WJG was estab-
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How to perform gastrointestinal ultrasound: Anatomy and
normal ndings
Nathan S S Atkinson, Robert V Bryant, Yi Dong, Christian Maaser, Torsten Kucharzik, Giovanni Maconi, Anil
K Asthana, Michael Blaivas, Adrian Goudie, Odd Helge Gilja, Dieter Nuernberg, Dagmar Schreiber-Dietrich,
Christoph F Dietrich
Nathan S S Atkinson, Translational Gastroenterology Unit,
Oxford University Hospitals NHS Foundation Trust, Oxford OX3
9DU, United Kingdom
Robert V Bryant, School of Medicine, University of Adelaide,
Adelaide, South Australia, 5005, Australia
Robert V Brya nt, Department of Gastroenterology and
Hepatology, Royal Adelaide Hospital, Adelaide 5000, Australia
Yi Dong, Department of Ultrasound, Zhongshan Hospital, Fudan
University, Shanghai 200032, China
Christian Maaser, Ambulanzzentrum Gastroenterologie,
Klinikum Lüneburg, 21339 Lüneburg, Germany
Torsten Kucharzik, Department of Gastroenterology, Städtisches
Klinikum Luneburg gGmbH, 21339 Lüneburg, Germany
Giovanni Maconi, Gastrointestinal Unit, Department of Biomedical
and Clinical Sciences, “L.Sacco” University Hospital, 20157
Milan, Italy
Anil K Asthana, Department of Gastroenterology and Hepato-
logy, The Alfred Hospital, Melbourne, Vic, Australia; Monash
University, Melbourne 3004 Vic, Australia
Michael Blaivas, Piedmont Hospital, Department of Emergency
Medicine, Atlanta, GA 30076, United States
Adrian Goudie , Fremantle Hospital and Health Service,
Emergency Department, Fremantle, WA 6160, United States
Odd Helge Gilja, National Centre for Ultrasound in Gastro-
enterology, Haukeland University Hospital, Bergen N-5021,
Norway
Odd Helge Gilja, Department of Clinical Medicine, University
of Bergen, 5021 Bergen, Norway
Dieter Nuernberg, Department of Gastroenterology, Brandenburg
Medical School, 16816 Neuruppin, Germany
Dagmar Schreiber-Dietrich, Christoph F Dietrich, Med.
Klinik 2, Caritas-Krankenhaus Bad Mergentheim, D-97980 Bad
Mergentheim, Germany
Author contributions: All authors contributed to this manuscript.
Conflict-of-interest statement: No potential conflicts of
interest. No nancial support.
Open-Access: 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/
Manuscript source: Invited manuscript
Correspondence to: Christoph F Dietrich, MD, PhD, Med.
Klinik 2, Caritas-Krankenhaus Bad Mergentheim, Uhlandstr. 7,
D-97980 Bad Mergentheim, Germany. christoph.dietrich@ckbm.de
Telephone: +49-7931-582201-2200
Fax: +49-7931-582290
Received: February 9, 2017
Peer-review started: February 11, 2017
First decision: April 25, 2017
Revised: May 30, 2017
Accepted: June 18, 2017
Article in press: June 19, 2017
Published online: October 14, 2017
Abstract
Gastrointestinal ultrasound is a practical, safe, cheap
and reproducible diagnostic tool in inflammatory
MINIREVIEWS
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Submit a Manuscript: http://www.f6publishing.com
DOI: 10.3748/wjg.v23.i38.6931
World J Gastroenterol 2017 October 14; 23(38): 6931-6941
ISSN 1007-9327 (print) ISSN 2219-2840 (online)

bowel disease gaining global prominence amongst
clinicians. Understanding the embryological processes
of the intestinal tract assists in the interpretation of
abnormal sonographic findings. In general terms, the
examination principally comprises interrogation of the
colon, mesentery and small intestine using both low-
frequency and high-frequency probes. Interpretation
of ndings on GIUS includes assessment of bowel wall
thickness, symmetry of this thickness, evidence of
transmural changes, assessment of vascularity using
Doppler imaging and assessment of other specific
features including lymph nodes, mesentery and luminal
motility. In addition to B-mode imaging, transperineal
ultrasonography, elastography and contrast-enhanced
ultrasonography are useful adjuncts. This supplement
expands upon these features in more depth.
Key words: Ultrasound; Intestinal; Inammatory bowel
disease; Guidelines; Teaching
Core tip: In general terms, gastrointestinal ultrasound
examination principally comprises interrogation of the
colon, mesentery and small intestine using both low-
frequency and high-frequency probes. In addition
to B-mode imaging, transperineal ultrasonography,
elastography and contrast-enhanced ultrasonography
are useful adjuncts.
Atkinson NSS, Bryant RV, Dong Y, Maaser C, Kucharzik
T, Maconi G, Asthana AK, Blaivas M, Goudie A, Gilja OH,
Nuernberg D, Schreiber-Dietrich D, Dietrich CF. How to perform
gastrointestinal ultrasound: Anatomy and normal ndings. World
J Gastroenterol 2017; 23(38): 6931-6941 Available from: URL:
http://www.wjgnet.com/1007-9327/full/v23/i38/6931.htm DOI:
http://dx.doi.org/10.3748/wjg.v23.i38.6931
INTRODUCTION
Gastrointestinal ultrasound (GIUS) is an accurate
diagnostic imaging tool for inflammatory bowel
disease[1-3]. Utilisation has steadily increased in different
global regions including Asia-Pacific[4]. To correctly
interpret GIUS ndings, it is necessary to have a rm
grounding in intestinal anatomy, the fundamentals of
ultrasonography, as well as the examination techniques
and approach. The indications for intestinal ultrasound
are wide-ranging including inflammatory bowel
disease, assessment of functional aspects and general
gastroenterological conditions such as diverticular
disease. Various educational theories are relevant in the
process of learning intestinal ultrasonography including
the learning process itself, using formative assessments
such as DOPS (direct observation of procedural skills),
adopting the apprenticeship or core competencies
model and formulation of a GIUS curriculum. These
principles and a process of learning GIUS have been
recently proposed[1].
The purpose of this paper is to review our know
ledge of intestinal embryology relevant to GIUS.
Understanding the origins and evolution of abdominal
structures during the embryological process can assist
in highlighting the reasoning behind abnormalities
found on GIUS. We then expand upon examination
techniques relevant to different segments of and
structures around the intestine, including an overview
of transperineal ultrasonography. We describe specic
intestinal luminal parameters to be assessed in GIUS
including special techniques such as contrastenhanced
ultrasound.
REVIEW OF INTESTINAL EMBRYOLOGY
In the 6th and 8th week of intrauterine life, the primitive
mid-gut intestinal tube elongates on the mesentery
around the superior mesenteric artery (SMA), her
niating into the umbilical cord. As the gut grows
and returns into the peritoneal cavity, it eventually
rotates 270 degrees counterclockwise, such that
the duodenum rests behind the SMA[1]. The caecum,
initially in the upper abdomen, descends to the right
lower quadrant. Thus the mesentery attachment of the
small bowel takes an oblique course from the duodeno
jejunal junction at the level of the left L2 process,
over the 3rd part of the duodenum, down to the level
of the right sacroiliac joint[5]. Though the mesentery
attachment is only 1520 cm long, it supplies a length
of small intestine approximately 40 times its length, a
feat achieved through progressive fanlike rufes. Seen
with traditional barium enterography, each curve of the
intestine has a concave and convex aspect, the concave
generally pointing towards the mesentery whilst
the convex aspect representing the antimesenteric
border[6]. These can be viewed in real time with GIUS.
Towards the end of the first trimester, the
peritoneum of the newly forming ascending colon
and the hindgut derived left colonic segments, begin
to fuse with the posterior abdominal wall. Although
traditionally described as retroperitoneal structures,
modern postmortem studies have found that two
thirds of the ascending and a third of the descending
colonic segments have mobile portions of elongated
mesentery[7]. Nonetheless, peritoneal attachments
have significance for the flow of free fluid within the
abdomen as uid tends to ow caudally, medial to the
ascending colon towards the ileocaecal junction and
thus metastatic deposits may become lodged in the
mesenteric rufes en route.
Relative thickenings of the mesocolon provide liga
mental support to the colonic exures; the nephrocolic
ligament runs from the inferior aspect of the right
kidney to the hepatic flexure which then becomes
intimately related to the descending duodenum before
the transverse mesocolon begins; the splenic exure is
suspended by (1) the phrenicocolic ligament which runs
from the diaphragm and also supports the spleen; (2)
the splenocolic; and (3) the pancreaticocolic ligaments
which are essentially extensions of the transverse
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Atkinson NSS
et al
. How to perform gastrointestinal ultrasound

mesocolon[5,7]. These attachments provide xed points
for ultrasound evaluation of the colon, which can at
times, be highly mobile within the abdomen.
The taenia coli, thickenings of the longitudinal
muscle layer grow from diffuse sheets at the caudal
end of the bowel, become more dened in the proximal
colon until they encase the caecum[6]. The taeniae
are one sixth shorter than the colon[5], forming the
haustrae. The muscle fibres in the longitudinal layer
end by turning at right angles to merge with the
circular bres and thereby acting as xed linkage points
for contraction. Contractions can occur asymmetrically
obliterating some haustrae, giving the false impression
of smallbowellike semicircular folds and bowel wall
thickening.
Vascular supply of the colon flows from the me-
senteric border, vessels spreading around the colon.
The vasa recta penetrate through oblique connective
tissue clefts in the bowel wall, the site of diverticular
protrusion, but importantly enter these clefts on the
antimesenteric aspect. In practice, diverticula are
rare on the anti-mesenteric border between the taenia
omonetalis and taenia libera. A vasa recta vessel
runs over the long aspect of each diverticulum before
entering the submucosa at the antimesenteric border[6].
EXAMINATION TECHNIQUE
General considerations and examination technique
An optimal environment for United States is within a
dedicated space or consulting room, offering indirect
low light sources and facilitating patient comfort. Prior
cross-sectional imaging and endoscopy reports should
be available to inform of postsurgical and anatomical
variants.
In most scenarios patient preparation is not re-
quired but specific measures can be used. Fasting
for 4-6 h decreases bowel motility whilst two cups
of water can be used to improve visualisation of the
duodenum[8]. Negative oral contrast may improve
detection of jejunal and proximal ileal stenosis, par
ticularly where examination findings are negative;
250-800 mL of polyethylene glycol solution generally
reaches the terminal ileum after an average duration
of 30 min[9]. Once contrast is seen to flow into the
caecum, retrograde examination of the small bowel can
be performed.
Examination of the intestinal tract begins with a
comfortable patient, relaxed in a supine position so as
not to tense the abdominal wall. The transducer is held
maintaining contact with the patient’s skin to gauge
pressure, whilst the left hand is free to optimize image
characteristics on the machine. A systematic approach
in examining the whole intestine is encouraged (Figure
1). Firstly, the low frequency 38 MHz (multifrequency)
curvilinear probe initially allows orientation to the
anatomy and detection of gross changes, whilst high
frequency linear probes (717 MHz) are preferable for
interrogating specic regions of interest in depth.
Colonic examination
Beginning at the right anterior superior iliac crest and
moving medially to the edge of the rectus muscles in
a sagittal plane, the common iliac (iliacal) vessels are
identied. Rotating anticlockwise to a transverse plane
and moving cranially, the rst bowel loop crossing from
medial to lateral is identified as the terminal ileum.
This is followed to the ileocaecal (Bauhin’s) valve and
caecum. The base of the appendix can be identified
at the deep margin of the caecum where the colonic
taenia meet before the ascending colon is followed
up towards the hepatic exure. The rest of the colon
can be followed via the transverse segment distally
towards the rectum. Alternatively, the same technique
can be used on the left side identifying the sigmoid
colon as the first loop of bowel crossing the left iliac
vessels, which can be followed to the descending colon
and towards the spleen as far as the rib margin allows.
The iliopsoas muscle can be used as an alternative
landmark for identification of the terminal ileum
and sigmoid colonic segments in the right and left
iliac fossae respectively. Intercostal imaging may be
required to visualise the left or splenic exure where
it has attachment to the spleen; elevating the left arm
and rotating to a partial right decubitus position with
a straight left leg can spread the ribs and improve
image acquisition (Figure 1C). Placing the probe in the
epigastric region in sagittal orientation demonstrates
the liver and stomach; one can then follow the
gastrocolic ligament to the transverse colon. Although
the transverse colon can be followed on ultrasound,
it may not be reliably viewed in its entirety. Be aware
that the rectum and distal parts of the colon cannot
always be displayed satisfactorily by transabdominal
United States. Transperineal imaging, in such cases,
can be useful to evaluate the distal rectum and perianal
tissues.
Mesentery and small intestine examination
Mesenteric fat is evident sonographically and is
considered to be abnormal if it extends over more
than half the circumference of the bowel loop, if it is
thickened beyond 56 mm or consistently greater than
the normal bowel wall thickness[10].
Examination of the mesentery begins in the
epigastrium at the duodenojejunal flexure which
then runs obliquely towards the right iliac fossa. To
aid visualization, the patient is asked to breath in
deeply and as they exhale, pressure is applied to the
transducer following which excellent views of the small
bowel mesentery sheets and abnormalities can be
achieved. A systematic scanning of the small bowel
may start in the right iliac fossa by dening the terminal
ileum and following its course in a proximal direction
as far as possible. Finally, a systematic overlapping
“Lawn Mowing” strategy is used, sweeping up and
down the abdomen to provide an overview of the small
bowel. This is performed with the probe in horizontal,
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Perineal ultrasound
TPUS allows visualisation of the perianal tissues, anal
canal, sphincters, the distal 57 cm section of the
rectum, vagina and a part of urinary bladder. A point
for orientation is the symphysis. Knowledge of the
pelvic anatomy is essential[12,13] (EFSUMB Case of the
Month). No specific patient preparation is required.
sagittal and oblique (parallel to the mesenteric
attachment) orientations in order to allow one’s eye to
follow structures and detect abnormalities. A full video
explanation of abdominal and intestinal ultrasound
examination technique is freely available on the
EFSUMB website[11] (www.efsumb.org/education/cfd-
videos001.asp).
A
B
Rectus
TI
IAV
Pelvic
wall
Rectus
Sigmoid
IAV
C
Rectus
Spleen SF
D
Rectus
SMA
Aorta
Figure 1 A systematic approach in examining the whole intestine. A: Examination begins in a relaxed ventral position; B: Beginning medial to the right anterior
superior iliac spine, the iliacal vessels (IAV) are identied and the rst bowel loop crossing medial-to-lateral is the terminal ileum (TI). The same technique on the right
identies the sigmoid colon; C: Elevating the arm spreads the rib spaces to improve visualisation of the splenic exure (SF); D: Gentle pressure as the patient breaths
out improves visualization of the mesentery and superior mesenteric artery (SMA) to exclude lymphadenopathy. The videos can be accessed via the efsumb website
[www.efsumb.org/education/cfd-videos001.asp].
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The patient is placed in the left lateral position as for
a digital rectal examination. The probe is covered in
either a sterile cover or an examination glove with
ultrasound gel between the layers.
Examination begins in the midline just above the
anus with the probe in a sagittal plane. The ultrasound
probe can be moved laterally, however angulated
views have reduced sensitivity for identification of
pathology. Fistulous tracts can be followed by first
placing the probe over the external opening. If
necessary, the probe can be placed in a coronal angle,
although this is usually less comfortable for the patient.
It is useful to start with an abdominal convex probe
(lower frequency) for the deeper structures and then
continue with a higher frequency probe (715 MHz).
Examination is also possible after rectal amputation
(e.g., QuénuOperation).
The anal canal, sphincter complexes, hemorrhoidal
plexus (Figure 2), rectovaginal plus anovaginal
septums, the walls of the vagina and distal rectum
can be defined. Fistulae should be classified as per
Parks’ classification[14] although TPUS has reduced
sensitivities for sphincteric relationships and therefore
the American Gastroenterological Association (AGA)[15]
distinction of “simple” from “complex” is of more clinical
utility; the former including low fistulae (superficial,
intersphincteric or intrasphincteric) below the dentate
line, with a single external opening and without
perianal complications or active proctitis[16]. Fistula and
abscesses visibility can be improved with ultrasound
contrast agents (UCA) using contrast enhanced ultra-
sound techniques[17,18]. Colour Doppler improves the
differentiation of inammatory reactions.
INTESTINAL LUMINAL FEATURES
Bowel wall thickness
Bowel wall thickness (BWT) is the measure most
consistently reported in diagnostic and activity
trials. Wall thickness of the alimentary tract differs
by region and depends on the degree of distension
and contraction[19,20]. The overall thickness should be
measured under mild compression from just above
an air-mucosal interface to the outside of the outer
muscularis propria layer border, including the whole
bowel wall[21]. Under these standardised conditions, the
stomach wall thickness measures 36 mm; terminal
ileum 13 mm; and colon 0.52 mm. In fact, the
normal range is likely to be even lower than this[22].
Values in children can be reliably obtained without the
need for sedation[22] but bear in mind that values do
increase over childhood[23] whilst still remaining < 2
mm. The optimal threshold for abnormal thickness is
debatable, as specicity improves with increasing wall
thickness at the cost of sensitivity (Figures 3 and 4).
Bowel wall layers
The GI wall has five layers that usually can be
visualized with ultrasound. The sonographic layers
are a combination of interface echoes and the echo
characteristics of the histological layers[24-26]. When
imaged in the anterior wall of a bowel loop starting
from the lumen the hyperechoic layer 1 corresponds to
the interface between the mucosa and the lumen and
is not a part of the actual GI wall. The hypoechoic layer
2 corresponds to the mucosa without the interface
between the submucosa and mucosa, the hyperechoic
layer 3 to the submucosa including this interface echo,
the hypoechoic layer 4 to most of the proper muscle
and layer 5 to the hyperechoic interface echo between
the proper muscle and the serosa.
Interface echoes are always hyperechoic and
located distally to the actual tissue interface. Therefore,
the correspondence between histology and sonographic
layers differ slightly in the dorsal wall. Specifically,
the interface between lumen and mucosa (layer 1)
is a part of the actual mucosa and layer 2 represents
the rest of the mucosa without muscularis mucosae,
which normally is covered by an interface echo and add
thickness to layer 3. Moreover, the interface between
submucosa and the proper muscle adds thickness to
layer 3 and reduces the thickness of layer 4. Finally, the
interface between the proper muscle and serosa (layer
5) extends beyond the actual serosa[27,28].
The interface from the serosa is hard to delineate.
Accordingly, the measurement should be made
from the start of the hypoechoic layer of the proper
muscle to the end of the hypoechoic layer of the
mucosa. Transducer-compression of the bowel wall
will reduce thickness and can make it challenging to
distinguish wall layers[29,30]. However, some operators
practice mild compression suggesting that this
improves reproducibility of measurements[21,22,3133].
The examiner should also be aware of interpretation
difculties due to mucosal folds and haustrations and
to keep the probe angle perpendicular to the bowel
wall to avoid tangential measurements. In conclusion,
dosed compression is a prerequisite for a reproducible
examination for some authors whereas others use it
with caution.
Figure 2 Example on the use of color doppler imaging and continous
duplex scanning. Perineal ultrasound showing the hemorrhoidal pleaxus using
color doppler imaging and continous duplex scanning with the typical spectrum
of the hemorrhoids.
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The layered wall structure changes with disease[34].
In severe disease the stratification may disappear
due to deep mural ulcers, increasing inflammatory
infiltrate and neovascularisation. In chronic inactive
disease, accentuated wall layers are more common.
The distinctions are less apparent with milder disease
phenotypes.
Symmetry
The symmetrical nature of changes is relevant. Asym
metry has been assumed to correspond to endoscopic
signs of focal ulceration or polypoid mucosal changes,
whilst diffuse thickening is evident with ulcerative colitis
(UC) or infectious colitis. The differential diagnoses for
chronic inflammatory bowel findings, with or without
asymmetry are listed in Tables 1 and 2.
Luminal diameter and motility
The small and large bowel can usually be distinguished
by scanning the haustrae of the colon and/or the
circular folds of Kerckring in the small intestine. In
unclear cases, scanning of the intestine during various
stages of lling may be helpful. Changes in Kerckring’s
folds and luminal uid quantity can be associated with
disease[35]. The small bowel diameter varies widely
depending on recent meals and activity, but dilatation
beyond 25 mm should be regarded as abnormal,
particularly when motility is reduced[36]. Assessment of
peristaltic activity and lumen compressibility are two
advantages of ultrasound over other imaging modalities.
Strictures may be identified by the coexistence of
thickened and stiffened bowel wall with narrowing of
the intestinal lumen, particularly if less than 10 mm[9].
The presence of proximal loop dilatation with fluid or
echogenic content is not required for the diagnosis[36]
but may carry clinical signicance.
Dilatation of the proximal small bowel loops with
hypo- or hyperperistalsis can be caused not only by
chronic brotic strictures but also by acute inammatory
stenosis or passenger invagination. Functional ultra
sonography is helpful in differentiation[37-40].
Extent of disease
Evaluating the length and extent of involved bowel
segments is performed by estimated longitudinal
AB
Mu SM
Lumen
Figure 3 Measurement of the bowel wall. The measurements are best taken ventrally since posterior artefacts occur (A) and the measurements (B) are not reliable.
Mu: Mucosa; SM: Submucosa.
Figure 4 Measurement of the bowel wall. In a patient with Crohn’s disease
of the small intestine, ultrasound was applied to evaluate disease extension
and wall thickness. B-mode image shows moderate wall thickening in the
ileum with well-preserved layer structure. Be aware the marked thickening
of the submucosal layer in white, often seen in IBD. The crosses mark the
wall thickness in the anterior and posterior wall denoting a slight difference in
thickening.
Crohn’s disease
Actinomycoses
Mycobacteria tuberculosis
Lymphoma
Neoplasia
NSAID enteropathy
Table 1 Differential diagnosis of asymmetrical terminal ileal
thickening with chronic symptoms
Inammatory bowel disease
Mycobacterium tuberculosis
Sarcoidosis
Diverticulitis
Neoplasia
Lymphoma
Ischemia
Tab le 2 Differential dia gnos is of c hron ic inflammatory
diseases of the bowel
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measurement and taking note of skip lesions. Bowel
wall thickening, luminal diameter for stenosis or
dilatation > 25 mm, and motility should be noted in
each region. Chronic inflammation tends to produce
an isolated, fixed segment without peristalsis and
abnormal angulation due to the brofatty proliferation
of the mesentery[41,42].
Transmural reactions
Transmural inammation and brosis may result in an
asymmetrically thickened, stratied bowel wall, which
are the typical findings of Crohn’s disease (CD). A
hypoechoic extension through the normal bowel wall
stratification correlates with cellular and oedematous
tissue inltration. Even though the extent of the bro
fatty proliferate correlates with the degree of intestinal
inammation in CD, there is no standardized method
to date to quantify the mesenteric fat by using GIUS.
Note should be made if the reaction extends beyond
the muscularis propria layer, and whether it does
so into the mesenteric or anti-mesenteric border.
Fistulae are identied as hypoechoic tracts extending
through the bowel wall, often with reverberations
(circumscribed bright air echoes) within them (Figure
5). Rounded hypoechoic areas (non-contrast imaging)
within the mesentry are suspicious for abscesses or
inflammatory phlegmons often with an irregular wall
or internal echoes (Figure 6). The occurrence of free
peritoneal fluid is important to note, though clinical
data corroborating its signicance are scant[21].
Fistulae and abscesses
Two prospective studies suggest a sensitivity and
specificity for the GIUS detection of fistulae of
72%87% and 90%96%, respectively[43]. This
performance is equivalent to CT/MR studies in meta
analysis[44], whilst small intestine contrast ultrasound
(SICUS) may have a sensitivity as high as 96%.
Estimates of the sensitivity and specicity for detecting
abscesses have been reported in a somewhat higher
range; 71%100% and 77%94% respectively[21,4549].
The direct application of contrast agents into the orice
of the stula may be helpful in determining the route
and connection(s)[12,13,50].
SECONDARY MESENTERIC FEATURES
Mesenteric lymph nodes
Lymph node enlargement is a frequent sonographic
finding in CD[10], however their interpretation and
clinical implications remain to be further clarified in
the literature. It has been suggested that they may
represent a very early manifestation of CD in children
for example[22]. They are correlated with duration
of disease and the presence of fistulae but more
importantly, for the ultrasound learner, they provide a
Airbubbles
ABC
Figure 5 Typical complications in Crohn’s disease, stula. Typical ultrasound ndings in Crohn’s disease include transmural inammation, stula and abscess
formation. A-C: The typical sign of stula is hypoechoic transmural inammation with (moving) air bubbles outside of the bowel lumen. The air bubbles are best
visualised using a real-time examination or video. Here we demonstrate single images of a video to demonstrate the changes within one second.
AB
Figure 6 Typical complications in Crohn’s disease, abscess. Typical ultrasound ndings in Crohn’s disease include transmural inammation, stula and abscess
formation. Contrast enhanced ultrasound allows to better delineate larger (A) and smaller abscess formation (B) not clearly suspected using B mode ultrasound.
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marker of procedural competence and interpretation. B
mode characteristics of lymph nodes to consider include
their length and particularly for those < 15 mm; their
short axis dimension should be less than half their
longitudinal diameter. Furthermore, the normal lymph
node architecture and hilum should be preserved in
normal or inammatory nodes[51].
Mesenteric inammation, oedema and vascularity
The supporting structures of the intestine run within
the sheets of mesentery, seen as layers of mixed
echogenicity with hyperechoic serosal layers on either
side, which does not have peristaltic movement
and appears similar in both transverse and sagittal
planes. Fat wrapping has long been recognised by
surgeons as a common and specic feature of CD. So
called (creeping) fat, extending from the mesenteric
attachment to partially cover the small or large
intestine resulting in loss of bowel mesentery angle,
is seen as an early event in the disease course and
plausibly plays a role in the inflammatory milieu[52].
In practical terms the serosal planes on either side
of the mesentery may be detected and should cover
less than half of the bowel circumference. It is also
the most common cause of bowel loop separation[41].
A subjective impression of increased thickening and
echogenicity has been applied in the literature[10],
correlating with clinical severity and primary luminal
findings; although in long standing disease it can
become more heterogeneous and hypoechoic[41].
TECHNIQUES FOR INTERROGATION OF
FEATURES OF INTEREST
Doppler imaging of tissue and SMA parameters
Colour Doppler imaging of the bowel wall is part of
standard assessment of the intestine and mesenterial
vessels (Figure 7). Hyperaemia is associated with
inflammation, usually seen in the submucosal layer
and the penetrating vessels of the muscularis propria.
Use of Doppler evaluation increases the sensitivity of
US for evaluating disease activity[33,39,5359]. The degree
of vascularity can be graded by the Limberg scale, a
semiquantitative assessment[60] that lacks routine
practical relevance. Other more complex quantitative
measurements of Doppler parameters have been
proposed, however a standardised protocol to com
pensate for confounders has not yet become widely
used. Power Doppler assessment of the arterial inow,
in particular the inferior mesenteric artery (IMA) for left
sided colonic disease and SMA for proximal colon and
small bowel activity, can be assessed in the majority of
patients and correlates with other ultrasound markers
of disease activity. It should therefore be interpreted
in the overall context of ultrasound findings[61]. A
prognostic role for Doppler parameters was previously
proposed[62] but awaits further study and validation.
Contrast-enhanced US
Second generation contrast agents such as SonoVue®,
produce harmonic frequencies from microbubbles
approximately the size of a single red blood cell,
and are stable within the circulation[17,63]. Imaging
systems thereafter allow visualisation of individual
blood vessels through a tissue and thereby improve
the accuracy of Doppler US in evaluating bowel wall
vascularity. This technique has been shown to be
useful in the assessment of disease activity in CD, in
particular differentiating inflammatory masses from
abscesses and may help to distinguish inflammatory
from brotic strictures in certain situations[64-66]. Use of
Contrast-Enhanced US (CEUS) during GIUS has been
standardized, does not requires specic expertise, and
its use in IBD presently is increasing[67].
Elastography
Similar to palpation, the elastic properties of a tissue
can be evaluated by assessing the speed of a sheer
wave through tissue or the amount of deformity
created by the sheer stress (strain imaging). Various
sonographic approaches to generating and measuring
these parameters are available[68], which may com
pliment standard B-mode assessment of a lesion.
Fibrotic lesions may appear stiff and inflammatory
lesions soft using elastography, which can help to
characterise intestinal lesions and has been correlated
with endoscopic ndings (Figure 8)[69,70].
CONCLUSION
Understanding the anatomy and embryology of the
intestinal tract is highly relevant in identifying sono
graphic abnormalities relevant to GIUS. The general
principles of examination involve specic interrogation of
the colon, small intestine and mesentery. Further work
is required to validate and understand the signicance
of certain sonographic parameters where understanding
is limited; this includes further evaluation of abnormal
wall thicknesses and quantifying this to a higher degree
of accuracy, understanding the signicance of peritoneal
fluid present as a reflection of transmural reactions,
Figure 7 Complications of inammatory bowel disease. Thrombosis of the
superior mesenteric vein. Partial recanalisation is shown by the markers.
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and the accurate interpretation and implications of
lymph nodes. Despite the presence of semiquantitative
measures, such as the Limberg score, they lack practical
relevance and so there is a need for further multicentre
prospective studies.
Various sonographic abnormalities can be detected
and interpreted currently but a standardized scoring
system for GIUS in inammatory bowel disease, akin
to validated endoscopic scores (such as the Ulcerative
Colitis Endoscopic Index of Severity) is lacking.
Ultimately, formulating a reproducible and validated
scoring system integrating different sonographic
parameters to reect severity will be highly relevant;
this will require agreement amongst GIUS experts and
validation in multicentre prospective studies. Finally, a
standardized method of documentation, including how
to capture images, needs to be developed.
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P- Reviewer: Capasso R S- Editor: Ma YJ L- Editor: A
E- Editor: Li D
Atkinson NSS
et al
. How to perform gastrointestinal ultrasound

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