Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 257
portal veins should be approximately the same size in any given liver region. The intrahepatic
biliary ducts, extrahepatic bile ducts, and hepatic arteries are not evident on a general
ultrasonographic examination unless they are enlarged. The common bile duct may be seen
coursing ventral, but parallel, to the portal vein. It should be less than 3 mm in diameter. The
gallbladder varies considerably in size; however, its ovoid shape is easily recognized and distinguished
from the hepatic vein and caudal vena cava. 10-13 Usually the gallbladder wall is
poorly visualized or not identified. When visible, the gallbladder wall is normally 2 to 3 mm
thick. Wall thickness and visibility vary with transducer frequency and placement. High-frequency
transducers directed perpendicular to the gallbladder wall are recommended when
gallbladder wall measurements are desired. Measurement of the wall closest to the transducer
is recommended. 13 A small amount of biliary sediment may be identified in a normal
fasting animal. A double gallbladder has been reported as an incidental finding in cats. This
produces a bilobed appearance (Fig. 3-9). The gallbladder may be bilobed, attached at the
neck, or arise from separate cystic ducts. 14
In obese animals, the falciform fat may interfere with attempts to obtain a good image of
the liver and, unless the sonographer is careful, may even be confused with the liver. The
echogenicity of the falciform fat in comparison to the liver can vary from being hyperechoic,
to hypoechoic, or isoechoic. The architecture of the falciform fat is usually more uniform than
that of the liver. It also contains numerous hyperechoic linear streaks, which are closer together
than the hyperechoic walls of portal veins. Liver lobes are more moveable during respiration
while the falciform fat is more stationary. A hyperechoic line may be visible at the interface
between the liver and falciform fat when the axis of the scan beam is perpendicular to the liver
surface. Identifying the architecture of the liver adjacent to the diaphragm and scanning caudally
toward the falciform fat are usually helpful in recognizing the difference in architecture
between the falciform fat and the liver, even when the liver is small.
Slice thickness artifacts are encountered frequently when examining the liver. The right
kidney, gallbladder, and fat in the porta hepatis can create the illusion of hepatic masses. 15
Careful examination by moving the transducer to several positions within the standard
sagittal or transverse planes will facilitate recognition of these artifacts.
Stomach. The stomach can be divided into four parts. The cardia is the point where the
esophagus joins the stomach, the fundus is the portion of the stomach to the left and
dorsal to the cardia, the major portion of the stomach is the body, and the pylorus, which
Fig. 3-8 Longitudinal sonograms of
the liver of a 4-year-old castrated
male Basset Hound with a history of
abdominal pain of 2 days duration.
The liver is normal. The gallbladder
is slightly distended, most likely
because the animal has not eaten
recently. The diaphragm can be seen
as a hyperechoic curved line. The
walls of the portal veins are hyperechoic.
Diagnosis: Normal liver.