Page 443 - Small Animal Internal Medicine, 6th Edition

CHAPTER 27 Diagnostic Tests for the Alimentary Tract 415

CYTOLOGIC EVALUATION OF FECES by abdominal palpation (e.g., gastric mass, foreign object,
splenic parenchymal mass). Plain radiographs should always
VetBooks.ir Fecal cytologic evaluations may identify etiologic agents be obtained before contrast-enhanced radiographs because
(1) the former may be diagnostic and eliminate the need
or inflammatory cells. In this method a thin, air-dried
smear is stained with Gram or a Romanowsky-type stain
be found to be contraindicated (e.g., evidence of GI tract
(e.g., Diff-Quik). The latter identifies cells better than Gram for contrast studies, (2) contrast-enhanced radiographs may
stain does. leakage), and (3) plain radiographs are needed to ensure a
Finding excessive numbers of spore-forming bacteria correct radiographic technique during the contrast proce-
(e.g., >3-4 per 1000× field) was once thought to strongly dure. Contrast-enhanced radiographs may be able to detect
suggest clostridial colitis (see Fig. 31.1). However, the pres- abnormalities (e.g., a gastric outflow tract obstruction) that
ence of spores is neither specific nor sensitive for clostridial plain radiographs cannot.
colitis. Finding that the bacterial population is relatively Radiographs are generally useful in the diagnostic workup
uniform morphologically is of uncertain value, other than to of animals with dysphagia, regurgitation, vomiting, abdomi-
show that the normal bacterial flora is disrupted. However, nal mass or distention, abdominal pain, or acute abdomen.
no comments can be made relative to cause or effect. They are occasionally helpful in animals with constipation,
Short, curved, gram-negative rods (i.e., “commas” or weight loss, or hyporexia of unknown cause, but other tests
“seagull wings”) are supposedly suggestive of campylobacte- are usually indicated first in such animals and often render
riosis, but the value of this test in dogs and cats is doubtful. radiographs unnecessary. Radiographic findings are rarely
The larger spirochetes, which are often plentiful in diarrheic diagnostic in dogs or cats with diarrhea or copious abdomi-
feces, are not C. jejuni and are of uncertain pathogenicity. nal effusion.
Fungal organisms (e.g., Histoplasma capsulatum, Cyniclomy-
ces guttulatus, Candida spp.) are rarely found by fecal exami-
nation; cytologic examination of mucosal scrapings or ULTRASONOGRAPHY OF THE
histologic examination of biopsy specimens is usually neces- ALIMENTARY TRACT
sary to diagnose histoplasmosis.
Leukocytes in feces indicate a transmural colonic inflam- Ultrasonography may be done in combination with or
mation instead of just superficial mucosal inflammation. instead of radiography. It is extremely operator dependent.
However, a definitive diagnosis of a particular cause is not It is often useful in animals with an acute abdomen, abdomi-
possible. nal effusion, vomiting, chronic diarrhea, weight loss, or
hyporexia of unknown cause and also in those with an
abdominal mass, distention, or pain. Ultrasonography often
ELECTRON MICROSCOPY identifies pancreatitis, infiltrations in various organs, and
intussusceptions that radiography misses. Furthermore,
Electron microscopy can be used to find various viral par- while effusions render radiographs useless, they enhance
ticles (e.g., coronavirus, parvovirus, astrovirus) in feces. ultrasonographic contrast. Ultrasonography is often more
Because ELISA is usually adequate for detecting parvovirus, informative than radiography for determining whether an
electron microscopy is rarely necessary. However, it is rea- animal with an acute abdomen requires surgery. Finally,
sonable to choose this technique if other test results are not ultrasonography can be used to guide percutaneous aspira-
diagnostic and there are epidemiologic considerations. Fecal tion and biopsy of intraabdominal lesions that would other-
samples for electron microscopy analysis should be obtained wise necessitate surgery or laparoscopy.
early in the disease because fecal viral concentrations may
decrease dramatically within 7 to 14 days after the onset of
signs. Furthermore, some delicate viruses (e.g., coronavirus) Techniques
degenerate quickly, and the feces from animals suspected of A 5-MHz probe is probably the most utilitarian. Hair is often
having such an infection must be handled appropriately if clipped so that there is no trapped air that could compromise
meaningful results are to be obtained. It is important that image quality.
clinicians contact their laboratory for instructions on sample
handling.
Findings
The thickness, echodensity, and homogeneity of organs (e.g.,
RADIOGRAPHY OF THE liver, spleen, intestine, stomach, mesenteric lymph nodes,
ALIMENTARY TRACT masses) may be assessed. Intraparenchymal infiltrates that
cannot be detected radiographically may also be found. The
Radiography allows evaluation of structures that cannot particular ultrasonographic findings seen in specific disor-
be adequately assessed during physical examination (e.g., ders of the alimentary tract are discussed in subsequent
esophagus, stomach) and may detect abnormalities missed chapters dealing with the disorders.