Barium sulfate suspension is used routinely for evaluation of the small intestines (upper GI series). Non-ionic, water-soluble
contrast agents with low osmolality have been shown to provide adequate opacification of the GI tract and may be used, especially
in smaller patients such as cats and pediatric patients.
Contrast studies and digital imaging
Digital imaging is being more commonly used in veterinary medicine. Early versions of digital radiography were limited in
spatial resolution; however, newer versions have overcome this problem. The advantages of digital radiography for contrast
radiography are much more rapid image acquisition, lower patient dose and high-contrast resolution. To maximize diagnostic
accuracy and efficiency of digital images, dedicated viewing work stations should be used with good monitor resolution and
Gastric diseases, outflow obstructions
Mechanical or functional (pyloric spasm) disorders often contribute to chronic vomiting. Differential diagnoses to consider
are hypertrophic pyloric stenosis, chronic hypertrophic gastropathy and inflammatory conditions, including inflammatory polyps
and neoplastic infiltrates. If available, digital fluoroscopy is an excellent tool to observe gastric motility after barium
sulfate administration. Gastric contractions against a spastic or narrowed pylorus result in typical radiographic appearance
of a "beak-sign" or "teat-sign" with a narrow contrast column entering the pyloric canal, whereas the antrum is distended.
Positioning will greatly influence gastric motility and pyloric outflow, right lateral recumbency facilitates emptying.
Delay of gastric emptying may be diagnosed with liquid barium. Normal emptying should begin within 15 minutes after barium
administration and should be complete within one to four hours in dogs and one to two hours in cats.
Because liquid barium better delineates lesions of the gastric wall, it usually is administered first. In some instances,
a barium meal (barium sulphate mixed with food) has to be administered as well, to reflect more closely the physiologic conditions,
followed by observation of gastric motility under fluoroscopy or by taking serial radiographs.
Gastric emptying time is difficult to evaluate, because addition of food significantly prolongs emptying and a wide normal
range exists (seven to 15 hours). Radiographic signs to look for are filling defects and narrowing of the pyloric lumen. Intraluminal
filling defects are caused by gastric foreign bodies, which can be moved to different gastric compartments by repositioning
the patient. Intramural filling defects result in focal wall thickening and are consistent with inflammatory lesions, severe
mucosal hypertrophy and, in some cases, neoplastic infiltrates. Diffuse, circumferential filling defects are seen with hypertrophic
pyloric stenosis, pyloric spasm, inflammatory or scar lesions of the pylorus and some neoplastic infiltrates.
Pedunculated gastric masses that protrude into the lumen can be delineated with negative contrast gastrography. The sensitivity
of double-contrast studies is much higher than simple contrast studies for mass recognition.
A small-sized mass often is completely obliterated by the contrast medium on simple positive contrast studies and often becomes
visible only on double-contrast studies. Nevertheless, the diagnosis is not always straightforward even on double-contrast
studies because artifacts caused by rugal folds or peristaltic activity can mimic gastric masses. A lesion should always be
confirmed on different projections.
Contrast studies (simple contrast gastrography or, preferably, double contrast gastrography) may be necessary to detect non-radiopaque
gastric foreign bodies, because they cannot always be differentiated from food on plain radiographs or abdominal ultrasound.
An upper GI study is a good choice of diagnostic work-up in a suspected gastric foreign body. Imaging findings include a filling
defect initially if the foreign body is large enough. Different patient positioning will determine in most cases if a filling
defect is freely moveable within the stomach (foreign body) or if it represents a rugal fold, wave of peristalsis or pedunculated
intramural gastric mass.
Smaller foreign bodies usually are obscured initially. A delay in gastric emptying may be observed. Since most foreign bodies
absorb some barium sulfate, a late post-contrast radiograph (after 12 hours) is often the diagnostic view because it shows
persistent barium within the stomach.