Diagnostic ultrasound ( PDFDrive )

CHAPTER 8 The Gastrointestinal Tract 269
Classic Features
Gut Wall Thickening
Gut wall thickening is the most frequently observed abnormality
in patients with Crohn disease and varies in proportion to disease
severity. Its identiication comprises the basis for initial disease
detection, for detection of recurrence, 24 and for determining the
extent of disease. In a meta-analysis on the accuracy of sonography
in detecting Crohn disease, Fraquelli et al. 25 showed sensitivity
and speciicity of 88% and 93%, respectively, when a bowel wall
thickness threshold greater than 3 mm was used, and 75% and
97% with a threshold greater than 4 mm.
Gut wall thickening in Crohn disease is most frequently
concentric and may be marked. 26,27 Wall echogenicity varies
depending on the degree of inlammatory iniltration and ibrosis.
Stratiication with retention of the gut layers is typical (Fig. 8.13A
and B; also see Fig. 8.2, Videos 8.2 and 8.3). A target or pseudokidney
appearance is possible in acute disease or long-standing
ibrotic or subacute inlammatory disease as the gut wall layering
is progressively lost (Fig. 8.13C and D). Long-standing and oten
burnt-out disease may also show wall thickening with fat deposition
in the submucosa, which appears as increased echogenicity
of this layer (Fig. 8.13E and F). Actively involved gut typically
appears rigid and ixed, with decreased or absent peristalsis (Video
8.4). Involvement of the serosal border of the bowel may result
in spiculation of the border of the bowel (Fig. 8.14). Skip areas
are frequent. Involved segments vary in length from a few millimeters
to many centimeters. Bowel wall thickening may be
caused by acute inlammatory change or related to chronic ibrosis
and smooth muscle hypertrophy.
Inlammatory Fat
Mesenteric edema and inlammation of the mesenteric fat are
also characteristic of Crohn disease, producing a mass in the
mesentery adjacent to the diseased gut that may creep over the
border of the abnormal gut or completely engulf it, the so-called
creeping fat. Fat creeping onto the margins of the involved gut
creates a uniform echogenic halo around the mesenteric border
of the gut, with a thyroidlike appearance in cross section (Fig.
8.15). It may become more heterogeneous and even hypoechoic
in long-standing disease. Creeping fat is the most common cause
of gut loop separation seen on GI contrast studies. 21 It is also
the most striking and detectable abnormality on sonography of
patients with perienteric inlammatory processes. herefore
detection of creeping fat should lead to a detailed evaluation of
the regional gut.
Lymphadenopathy
Tender and enlarged mesenteric and perienteric nodes are
common features of the active phase of inlammation with
Crohn disease (Fig. 8.16). Lymphadenopathy may persist in the
inactive phase. he nodes appear as focal hypoechoic masses
circumferentially surrounding the gut and in the expected
location of the mesenteric attachment. Nodes are frequently
quite round, are of moderate size, and typically lose the normal
linear echogenic streak from the nodal hilum. Similar to the
gut, the lymph nodes show hyperemia as a relection of their
inlammation.
Hyperemia
Mesenteric vascularization and neoangiogenesis are recognized
components of the inlammatory process, and evaluation of blood
low is a useful tool for monitoring inlammatory activity and
response to therapy. Disease activity correlates with hyperemia,
as seen on color Doppler evaluation 28 (Fig. 8.17, Video 8.5).
Although subjective, this addition of color Doppler to gray-scale
sonography can provide valuable supportive evidence of inlammatory
change in the gut and adjacent inlamed fat 21 (see Fig.
8.6B, D, and F). However, color Doppler shows blood low in
major blood vessels with relatively fast-moving blood and does
not show blood low at the perfusion level. To overcome this
limitation of activity assessment, there has been increasing interest
over recent years in the use of CEUS of the bowel, performed
with the injection of microbubble contrast agents. Using ultrasound
quantitative techniques, CEUS allows for objective measurement
of blood low at the perfusion level as a relection of activity.
On observation, we look for transmural enhancement of the
bowel wall and also a “comb sign,” relective of blood low within
the mesenteric vasculature (Fig. 8.18, Videos 8.6 and 8.7).
Generation of time intensity curves allows for measurement of
the peak enhancement and the area under the curve. Studies
have shown a direct correlation between the level of bowel wall
enhancement and active inlammatory disease, as assessed on
colonoscopy. 29,30 Further, Ripollés et al. 29 show that CEUS measurements
perform better than wall thickness in prediction of disease
severity at colonoscopy. In our own laboratory, we have integrated
the objective measurements of blood low on CEUS with the
baseline gray-scale assessments of wall thickness and inlammatory
fat to improve the objectivity of activity assessments on
ultrasound. 23
Mucosal Abnormalities
Although endoscopy remains the major tool for evaluating
mucosal and luminal abnormality, ultrasound may on occasion
show luminal polypoid masses, such as inlammatory polyps,
and deep ulcerations with pockets of echogenic air projecting
within the gut wall. Ultrasound may also show intramural
sinus tracts with air dissecting within the layers of the bowel
wall (Fig. 8.19), as a complication of both Crohn disease and
diverticulitis.
Conglomerate Masses
Conglomerate masses may be related to clumps of matted bowel,
inlamed edematous mesentery, increased fat deposition in the
mesentery, or, infrequently, mesenteric lymphadenopathy. Involved
loops may demonstrate angulation and ixation resulting from
retraction of the thickened ibrotic mesentery.
COMPLICATIONS
Strictures
Strictures are the most common complication of Crohn disease
requiring surgical intervention. hese are due to rigid narrowing
of the gut lumen, contributed to by mural inlammation, ibrosis,
and smooth muscle hypertrophy. he luminal surfaces of involved