Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

280 Small Animal Radiolo g y and Ultrasono graphy
Often lesions of the stomach will be seen clearly on the ventrodorsal or dorsoventral
view and not on the lateral view. The paramount principle in evaluating a GI series is the
repeatability of viewing a lesion at least on multiple radiographs, if not in multiple positions.
Thus a study that has a limited number of radiographs may be nondiagnostic. If a
structure appears abnormal on one film but does not remain constant in appearance on at
least the same view throughout the series, it should be regarded as spurious and the study
findings should be considered normal. The GI series is a poor evaluator of physiologic
function and is a more accurate evaluator of gross anatomical change. The large intestine
should not be evaluated with the GI series. This is because of the lack of colon distention.
To evaluate the colon radiographically a pneumocolon, barium enema, or double-contrast
enema should be performed.
Double-Contrast Gastrogram. In most instances the stomach can be evaluated adequately
by the combination of survey radiography and a GI series. The double-contrast
gastrogram is recommended for those conditions requiring evaluation of relatively minor
anatomical changes. 12,108-110 Because of the use of glucagon, this procedure may be contraindicated
in animals with diabetes mellitus. Fluoroscopy is recommended, but not
required, to perform this procedure. The patient should be anesthetized or heavily tranquilized.
Immediately prior to the procedure, glucagon is injected intravenously (0.1 mg
for small dogs to 0.35 mg for large dogs) after which a 100% weight-to-volume barium suspension
is administered via a stomach tube at a dosage of 1.5 to 3.0 ml/kg. Following this,
the stomach is distended with air until it is tympanitic (approximately 20 ml/kg) upon percussion.
Immediately after the contrast agents have been administered, a minimum of four
views, ventrodorsal, dorsoventral, left lateral, and right lateral, are taken and additional
oblique views may be needed to ensure that every gastric surface is fully evaluated.
Pneumocolon. The easiest radiographic special procedure for the evaluation of the colon
is the pneumocolon. 12,111 Preparation of the abdomen is not as important as it is for the
GI series. The procedure is performed by inserting a catheter or syringe tip through the rectal
sphincter and injecting 1 to 3 ml of air per kg of body weight. Lateral and ventrodorsal
views are then exposed. Based on the appearance of the radiographs, more air may be
added as needed. The technique is useful for evaluating the colon and rectum for intraluminal,
intramural, and extraluminal lesions. It can be used to demonstrate the cranial
extent of a mass or stricture that narrows the lumen of the colon too much for passage of
an endoscope. It is also useful for identifying the location of the colon and distinguishing
it from distended small intestine.
Barium Enema and Double-Contrast Enema. Evaluation of the colon also may be accomplished
by the barium or double-contrast enema. Preparation of the colon using multiple
enemas or laxatives is essential, because the colon must be emptied prior to the study. Fecal
material within the lumen of the colon may mimic or obscure a lesion. This contrast technique
rarely is used, because evaluation of the colon using a rigid or flexible colonoscope or
proctoscope is relatively easy. Colonoscopy has the advantage of directly visualizing lesions,
determining their extent, and potentially obtaining a biopsy or cytologic specimen. If the
lesion is not accessible with the equipment available and a pneumocolon will not provide
sufficient information, a contrast enema is indicated. The patient must be anesthetized. A
15% to 20% weight-to-volume barium suspension is instilled at a dosage of 22.2 ml/kg via
a cuffed enema tube. 12,112 Lateral and ventrodorsal views should be taken. The barium is
then drained from the colon, which is then insufflated with an equal volume of air to create
a double-contrast enema. Lateral and ventrodorsal radiographs are taken.
ABNORMAL FINDINGS
G E N E R A L A B D O M E N
Body Wall. Radiographic changes in the size or shape of the body wall are limited to either
increases or decreases in thickness or disruption of continuity. Increases in body wall thickness
may be focal or diffuse. In focal thickening, the diagnosis may be suggested by the den-