Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 323
ographically but can cause outflow obstruction. 333 Mucosal hypertrophy may be symmetric
or asymmetric and may be evident only when a wave of peristalsis pushes the contrast
material into the pylorus. When this occurs, the normal pylorus should be convex on both
the cranial and caudal aspects. Mucosal hypertrophy may produce a concavity or flattening
on one side. This should be evident in more than one radiograph during the GI series.
Double-Contrast Gastrography
Ulcers. The double-contrast gastrogram is most helpful in evaluating the stomach for
benign ulcers, but it is also useful in evaluating some mass lesions. 110,193 Benign gastric
ulcers, which may be difficult to detect on a standard GI series, may become more readily
apparent in the double-contrast study. When evaluating this study, the effects of gravity on
the contrast medium and the normal gastric anatomy must be considered (Fig. 3-89). If
located on a nondependent surface, the ulcers will be seen as lines running in directions
other than the normal gastric rugal folds. On dependent projections, the barium will puddle
in the ulcer crater (Fig. 3-90).
Intramural and Intraluminal Lesions. The double-contrast gastrogram may be
helpful in evaluating some cases of gastric carcinoma or other gastric wall masses, particularly
if the masses are small or not located on one of the surfaces that is seen clearly
on the regular GI series (Fig. 3-91). The contrast or air can be used to highlight the lesion
by positioning the patient so that the lesion is dependent (surrounded by barium) or up
(surrounded by air). The position of a filling defect during a double-contrast gastrogram
is helpful in distinguishing between intramural and intraluminal objects. Intraluminal
objects will move freely within the gastric lumen and will therefore move with the barium
during the double-contrast examination. Intramural objects will remain fixed in
location and will therefore be outlined with air on one view and with barium on the
opposite view.
Abnormal Gastric Ultrasonography. The stomach can be evaluated from left to right in a
systematic fashion in both the longitudinal and transverse planes. Gastric wall symmetry
can be observed and wall thickness can be measured, wall layers can be identified, extent of
a wall lesion can be determined, and peristaltic activity can be observed. 18,334-336 The
lumen of the stomach also can be evaluated provided the stomach contains fluid without
a large amount of air or ingesta. In some animals, it may be necessary to fill the stomach
with fluid to facilitate the ultrasonographic examination. This is rarely necessary but can
be accomplished easily without sedation of the patient.
Thickening of the gastric wall is the most common sonographic abnormality
seen. 336 It must be interpreted cautiously because false-positive examinations have
occurred. 337 Gastric wall thickening may be local or diffuse and symmetric or asymmetric.
338-343 Both tumors and granulomas produce local asymmetric thickening with
disruption of the layers of the gastric wall (Fig. 3-92). Generalized thickening may occur
with either inflammatory disease or infiltrative neoplasia (Fig. 3-93). Infiltrative neoplasia
may disrupt the gastric wall and interfere with identification of the wall layers to
a greater extent than inflammatory disease. 336 Gastric lymphoma has various manifestations.
However, in cats a transmural circumferential lesion with disruption of the
normal gastric wall architecture, decreased echogenicity, and local interference with
peristalsis was the most common form observed. 338,339 Lymph node involvement was
commonly identified.
Intramural masses may be detected and may produce discrete rounded or lobulated
lesions, which may be outlined by fluid within the gastric lumen. Localizing the mass to a
distinct layer of the stomach is difficult. Most gastric masses are heteroechoic, and characterizing
the mass as neoplastic or inflammatory is not possible. Observing the motion of
the mass with change in position of the patient or gastric peristalsis is useful in determining
whether the mass is intramural or intraluminal. Intramural lesions will be fixed in position
despite peristalsis or changes in patient position. Intramural masses may also interfere
with normal wall movement during peristalsis.
It is more difficult to recognize diffuse gastric wall thickening. If the gastric wall diameter
exceeds the normal range of 3 to 5 mm, the wall layers should be examined to see if they