Page 328 - Feline diagnostic imaging

336 21 Normal Gastrointestinal Anatomy

(a) measure gastric emptying and intestinal transit times.
Retention of the larger spheres in the stomach is consistent
with a pyloric outflow obstruction or obstruction in the
proximal small intestine. Bunching at other locations with
dilation of the associated bowel is consistent with obstruc-
tion more distally. In a study evaluating gastric emptying,
the smaller spheres were seen to collect in the pyloric
region of the stomach at three hours. In half of the cats in
this study, food was seen to leave the stomach faster than
the small spheres [12].

21.2.2 Esophagography
(b)
Air does not normally stay in the esophagus but a small
amount may be seen as it is being swallowed. Persistent gas
or visible dilation may signal a problem and occasionally
gas can outline a fluid‐opaque foreign body that would oth-
erwise not be seen. Survey radiographs should always be
obtained prior to contrast radiography to document change
or possibly reveal preexisting abnormalities.
Routine esophagography is quick and easy to perform
and no preparation or sedation is required (Figure 21.6).
In order to be useful, the chosen contrast medium must
coat the esophageal mucosa to provide residual contrast
that can be seen on the radiographs. Barium paste is used
for most esophagrams but should not be given if aspiration
is likely to occur. The thick paste could plug small bron-
chioles. A small amount of aspirated barium will usually
be tolerated but barium that reaches the alveoli will
Figure 21.3 (a) Barium can be seen in the trachea and
bronchial tree (arrows) of this cat. (b) Most of the barium was remain. Nonionic contrast medium that is isotonic to
coughed up but some reached the alveoli. A small amount of blood may also be safe. If perforation of the esophagus is
barium is usually well tolerated but can be seen years following suspected, iodinated liquid contrast medium should be
aspiration. If a stomach tube is used to administer barium, care given first. Alternatively, endoscopy could be performed.
must be taken to ensure proper placement. Aspiration of a large
amount of barium is fatal. Lateral and ventrodorsal oblique radiographs should be
exposed immediately after the paste or other contrast is
Air is usually used as a negative contrast agent; carbon swallowed.
dioxide is less commonly used. Double‐contrast radiog- In a normal esophagram, the mucosa should be coated
raphy refers to the use of both positive and negative but there should not be retention of much barium. Contrast
contrast. Contrast procedures of the GIT include esoph- should not be visible in the pyriform recesses, nasophar-
agography (using paste or a barium burger), upper GI ynx, larynx, or trachea but a small amount of contrast in
series, pneumogastrogram, barium enema, and pneumo- the esophagus immediately distal to the cranial esophageal
colography. A contrast procedure is appropriate when sphincter is normal. Fine linear striations should be seen
diagnosis or determination of the course of therapy can- running longitudinally from the cricopharyngeus caudally
not be made from survey radiographs and other clinical along the proximal two‐thirds of the esophagus. The distal
information. It is important to always expose survey one‐third of the esophagus presents with transverse stria-
films first because they provide a baseline and might tions referred to as a herring bone or fish bone pattern
even provide a diagnosis. (Figure 21.4b). In a single radiograph, a small dilated area
Barium‐impregnated polyethylene spheres (BIPS) have may represent a bolus being swallowed but the exposure
been proposed as an alternative for a conventional upper should be repeated to ensure that a lesion is not present. If
GI series [11]. BIPS come in two sizes, 5 and 1.5 mm, and no abnormalities are seen with barium paste, esophagogra-
are dispensed in capsules (Figure 21.5). The larger spheres phy can be repeated with liquid barium suspension mixed
are intended to detect obstruction while the smaller spheres with canned cat food.