Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

354 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-128 A 10-year-old female
Standard Poodle with dyschezia for 4
months and hematochezia for 1
week. On the survey radiographs
there was a suspicious tissue density
in the distal descending large intestine
and marked distention proximal
to this. The lateral view of the pneumocolon
revealed that the rectum is
normal. There is a tissue-dense mass
involving the descending large intestine
with a small defect in its middle,
suggestive of a residual lumen (open
white arrow). Proximal to the mass,
the large intestine is severely dilated.
Differential diagnoses include neoplasia
(adenocarcinoma) or granuloma.
Diagnosis: Adenocarcinoma
of the distal large intestine.
mass adjacent to the colon or cecum. Some degree of small intestinal obstruction also may
occur. The mass will not alter the smooth mucosal surface of the cecum or colon. Perirectal
tumors (perianal masses or metastases) may affect the colon but usually are apparent without
contrast studies.
Ultrasonography of Colonic and Cecal Abnormalities. The colon does not lend itself to
ultrasonographic examination very well because it usually contains air. The colon wall can
be evaluated by ultrasonography, although the layers described for the stomach and small
bowel cannot be delineated as clearly. The bright mucosal-submucosal stripe is still identifiable.
The thickness of the wall also can be determined, with the thickness limits approximately
the same as those of the small bowel. Diffuse thickening of the colon wall may be
observed in inflammatory and infiltrative disease such as infectious or lymphocytic plasmacytic
colitis (Figs. 3-129 and 3-130). The ultrasonographic findings are nonspecific.
Focal areas of thickening and heteroechoic masses also may be detected. These may be neoplasms
or granulomas. The terminal colon and rectum are hidden from ultrasonographic
examination by the pelvic canal. Transrectal ultrasonography may be used to evaluate the
rectum; however, the information that can be gained about the colon wall is minimal and
diagnosticians are better served by endoscopic or radiographic techniques.
In rare cases, the cecum can be identified separately from the colon. Cecal inversion
may produce a structure within the colon that is similar to an intussusception. In long-axis
views, linear streaks of hyperechoic and hypoechoic tissue will be seen, and in transverse
views a series of concentric rings may be observed. The length of the cecal inversion will be
shorter than most intussusceptions.
A B D O M I N A L LY M P H A D E N O PAT H Y
The normal mesenteric, portal, and related lymph nodes are not visible radiographically.
Lymph nodes can be imaged sonographically, but they are not usually conspicuous. 9,61
These appear sonographically as ovoid and uniform bodies with a grainy echo texture
somewhat similar to spleen or testicle. Any mass not specifically part of an abdominal
organ may be an enlarged lymph node as well as a neoplasm, a granuloma, or a hamartoma.
Lymph node enlargement may be the result of stimulation (e.g., reactive lymph
node) or it may be due to infiltration (e.g., multifocal origin or nodal extension from a
primary site of disease). The latter process is usually from neoplastic sites. Abdominal
lymphadenopathy, particularly of the nodes associated with gut and liver, may be the first