Diagnostic ultrasound ( PDFDrive )

CHAPTER 8 The Gastrointestinal Tract 281
A
B
FIG. 8.28 Perianal Inlammatory Crohn Disease. (A) Axial image of the anal canal shows an internal opening (arrow) posteriorly at 6 o’clock.
A transsphincteric istula runs to a large, horseshoe-shaped posterior abscess more optimally shown in (B), which also shows deeper collections
in the left buttock.
air) or retroperitoneal, and its presence should suggest either
hollow viscus perforation or infection with gas-forming organisms
40 (Fig. 8.29). Nonluminal gas may be easily overlooked,
particularly if the collection is large. Gas in the wall of the GI
tract, pneumatosis intestinalis, with or without gas in the portal
veins, raises the possibility of ischemic gut.
he likelihood of gas artifacts between the abdominal wall
and the underlying liver to be related to free intraperitoneal gas
was well described by Lee et al. 40 In my group’s work, we have
found that the peritoneal stripe appears as a bright, continuous,
echogenic line, and that air adjacent to the peritoneal stripe
produces enhancement of this layer, because the gas has a higher
acoustic impedance to sound waves than does the peritoneum
itself. Careful peritoneal assessment is best done with a 5-MHz
probe or even a 7.5-MHz probe, with the focal zone set at the
expected level of the peritoneum. In a clinical situation, enhancement
of the peritoneal stripe is a highly speciic but insensitive
sign to detect pneumoperitoneum. 41
Loculated luid collections can mimic portions of the GI
tract. Let upper quadrant and pelvic collections suggestive of
the stomach and rectum may be clariied by adding luid orally
and rectally. Assessing peristaltic activity and wall morphology
also helps in distinguishing luminal from extraluminal collections.
Interloop and lank collections are aperistaltic and tend to correspond
in contour to the adjacent abdominal wall or intestinal
loops, frequently forming acute angles, which are rarely seen
with intraluminal luid.
he appearance of the perienteric sot tissues is frequently
the irst and most obvious clue to abdominal pathology on
abdominal sonograms. Inlammation of the perienteric fat shows
as a hyperechoic mass efect (see Fig. 8.15), oten without the
usual appearance of normal gut and its contained small pockets
of gas. Neoplastic iniltration of the perienteric fat is oten
Acute Abdomen: Sonographic Approach
GAS
Intraluminal
Extraluminal
Intraperitoneal
Retroperitoneal
Gut wall
Gallbladder/biliary ducts
Portal veins
FLUID
Intraluminal
Normal caliber gut
Dilated gut
Extraluminal
Free
Loculated
MASSES
Neoplastic
Inlammatory
Perienteric Soft Tissues
Inlamed fat
Lymph nodes
Gut
Wall
Caliber
Peristalsis
Clinical Interaction
Palpable mass
Maximal tenderness
Sonographic Murphy sign
Sonographic McBurney sign