Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

298 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-50 A 10-year-old neutered
female domestic short-haired cat with
a slight lump and mass on the left
elbow. Physical examination revealed
a palpably irregular cranial abdominal
mass. The lateral radiograph revealed
moderate hepatomegaly and clearly
irregular ventral borders of the liver
(open black arrows). Laparotomy
revealed multiple hepatic masses.
Diagnosis: Hepatic cystadenoma.
caudal lung lobes it will be almost totally inaccessible to ultrasonographic examination.
This does not indicate that the liver is small. Radiography is preferred to ultrasonography
for determining liver size.
Shape Changes. Alterations in contour of the liver can be recognized using ultrasonography.
These changes can be observed if the margins of the liver are examined carefully.
Oblique or off-axis views may be helpful in evaluating the contour of the liver. Minor
irregularities can be detected and any irregularity should be considered abnormal.
Rounded liver margins may be observed when the liver is enlarged. Although a common
cause of these irregularities is tumor, this also can occur with cirrhosis and nodular
regeneration.
Changes in Echo Intensity and Pattern. The echo intensity and pattern of the liver
parenchyma are the most important features of the liver examination. The liver is usually
hypoechoic when compared with the spleen and slightly hyperechoic when compared with
the kidney. This relative echogenicity can be used provided the spleen and kidney are normal.
With experience, a subjective impression of the “brightness” of the liver may be
gained; however, this subjective impression is not totally reliable. The alteration in
echogenicity of the liver may be diffuse or focal. Focal changes are easier to detect because
the surrounding hepatic parenchyma will be normal. Diffuse changes are not detected
easily and may be artifactual. 265 A diffuse increase in echogenicity of the liver is nonspecific
and may occur as a result of lymphosarcoma, fatty infiltration, fibrosis (cirrhosis), or
steroid hepatopathy (Figs. 3-51 and 3-52). 266 A diffuse decrease in echogenicity may be
associated with diffuse neoplasia (i.e., lymphoma) and hepatic congestion. 267,268 Hepatitis
may be hyperechoic, hypoechoic, or heteroechoic, depending on the stage or severity of the
disease. Focal changes in hepatic echo intensity may result in lesions that are hyper- or
hypoechoic, or a combination of the two. 265,269
If it is mild, a fatty infiltration of the liver may not produce radiographic changes. In
some patients, diffusely increased echogenicity with liver enlargement may be recognized.
An increased attenuation of the sound beam may be associated with fatty infiltration
of the liver and may create a false impression that the liver is hypoechoic in its
deeper portion. In cats, the ultrasonographic finding of a liver that was hyperechoic
when compared with the echo intensity of the falciform fat was identified as a criterion
for diagnosis of severe hepatic lipidosis. 270,271 However, further studies revealed that it is