Diagnostic ultrasound ( PDFDrive )

CHAPTER 8 The Gastrointestinal Tract 257
Recent years have shown growing interest in the use of ultrasound
for surveillance of patients with inlammatory bowel disease.
Further, endosonography, performed with high-frequency
transducers in the gut lumen, is an increasingly popular technique
for assessing the esophagus, stomach, and rectum.
ANATOMY AND SONOGRAPHIC
TECHNIQUE
The Gut Signature
he gut is a continuous hollow tube with four concentric layers
(Fig. 8.1). From the lumen outward, these layers are (1) mucosa,
which consists of an epithelial lining, loose connective tissue (or
lamina propria), and muscularis mucosa; (2) submucosa; (3)
muscularis propria, with inner circular and outer longitudinal
ibers; and (4) serosa or adventitia. hese histologic layers correspond
with the sonographic appearance 1-3 (Table 8.1) and are
referred to as the gut signature, where up to ive layers may be
visualized (Fig. 8.2).
he sonographic layers appear alternately echogenic and
hypoechoic; the irst, third, and ith layers are echogenic, and
the second and fourth layers are hypoechoic. his relationship
TABLE 8.1 Gut Signature: Histologic-
Sonographic Correlation
Histology
Supericial mucosa/interface (epithelium
and lamina propria)
Muscularis mucosa
Submucosa
Muscularis propria (inner circular and
outer longitudinal ibers)
Serosa/interface
Submucosa
Mucosa
Epithelium
Lamina propria
Muscularis mucosa
Muscularis
propria
Sonography
Echogenic
Hypoechoic
Echogenic
Hypoechoic
Echogenic
FIG. 8.1 Schematic Depiction of the Histologic Layers of the Gut
Wall.
of the histologic layering with the sonographic layering is best
remembered by recognition that the muscular components of
the gut wall—the muscularis mucosa and the muscularis
propria—constitute the hypoechoic layers on sonography.
On routine sonograms, the gut signature may vary from a
“bull’s-eye” in cross section, with an echogenic central area and
a hypoechoic rim, to full depiction of the ive sonographic layers.
he quality of the scan and the resolution of the transducer
determine the degree of layer diferentiation. Ultrasound is
superior to both computed tomography (CT) and magnetic
resonance imaging (MRI) for resolution of the gut wall layers.
he normal gut wall is uniform and compliant, with an average
thickness of 3 mm if distended and 5 mm if not. Other morphologic
features that allow recognition of speciic portions of
the gut include the gastric rugae (in the stomach), valvulae
conniventes (plicae circulares in the small intestines), and haustra
(in the colon) (Fig. 8.3).
Real-time sonography allows assessment of the content and
diameter of the GI lumen and the motility of the gut. Hypersecretion,
mechanical obstruction, and ileus are implicated when gut
luid is excessive. Peristalsis is normally seen in the small bowel
and stomach. Activity may be increased with mechanical obstruction
and inlammatory enteritides. Decreased activity is seen
with paralytic ileus and in the end stages of mechanical bowel
obstruction.
Gut Wall Pathology
Evaluation of thickened gut on sonography is far superior to the
evaluation of normal gut for two important reasons. hick gut,
particularly if associated with abnormality of the perienteric sot
tissues, creates a mass efect, which is easily seen on sonography.
In addition, thickened gut is frequently relatively gasless, improving
its sonographic evaluation. Gut wall pathology creates
characteristic sonographic patterns (Fig. 8.4). he most familiar,
the target pattern, was irst described by Lutz and Petzoldt 4 in
1976 and later by Bluth et al., 5 who referred to the pattern as a
“pseudokidney,” noting that a pathologically signiicant lesion
was found in more than 90% of patients with this pattern. In
both descriptions the hypoechoic external rim corresponds to
thickened gut wall, whereas the echogenic center relates to residual
gut lumen or mucosal ulceration.
Identiication of thickened gut on sonographic examination
may be related to a variety of diseases. Diagnostic possibilities
are predicted by determining the (1) extent and location of
disease, (2) preservation or destruction of wall layering, and (3)
concentricity or eccentricity of wall involvement. Benignancy is
favored by long segment involvement with concentric thickening
and wall layer preservation. he classic benign pathology showing
gut wall thickening is Crohn disease. Malignancy is favored by
short segment involvement with eccentric disease and wall layer
destruction. he classic malignant pathology showing gut wall
thickening is adenocarcinoma of the stomach or colon. hese
are guidelines rather than rules, because chronically thickened
gut in Crohn disease may show layer destruction related to
ibrotic and subacute inlammatory change, and iniltrative
adenocarcinoma may show some wall layer preservation.
Lymphadenopathy and hyperemia of the thickened gut wall