Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 307
Fig. 3-67 A 5-year-old neutered
female domestic short-haired cat
had vomiting and jaundice. This is
the same case as seen in Fig. 3-41. An
oblique sonogram revealed a dilated
common bile duct containing two
calculi (arrows) near the duodenum.
Diagnosis: Choledocholithiasis with
bile duct obstruction.
Portosystemic Shunts. Several contrast procedures may be useful when portosystemic
shunts are suspected. Regardless of the method used, the portal vein should be seen
branching into several intrahepatic radicals (Figs. 3-68 and 3-69). After passing through
the liver, the contrast medium should enter the hepatic vein and then pass into the caudal
vena cava. Shunts may go from the portal vein to the azygous vein, perirenal veins,
perineal venous structures, or caudal vena cava (whether from posthepatic portal caval
shunts or a persistent patent ductus venosus) (Figs. 3-70 to 3-72). 291,292,294-302
Identification of the presence of portal radicals is important as a prognosticator for successful
surgical intervention in animals with shunts. The presence of intrahepatic portal
radicals suggests that partial or complete ligation of the shunt(s) probably will be helpful.
Portosystemic shunts can be detected using ultrasonography if the patient is cooperative
and the stomach is not too distended. 303-314 The portal vein and caudal vena cava must
be identified and traced cranially or caudally. The shunt vessel may be observed connecting
the portal vein and the vena cava. The portal vein and caudal vena cava are close
together in the porta hepatis, and caution must be used when examining this area to ensure
that a shunt is not diagnosed incorrectly. Failure to identify the shunt does not exclude the
diagnosis. Alteration in the course of the portal vein or tortuosity of the portal vein is suggestive
of a shunt, even though the communication is not obvious (Figs. 3-73 and 3-74).
The diagnosis should be confirmed by other studies, such as portovenography or technetium
transcolonic portography. 315-317 Other shunts, such as portal azygous or portal
renal, may be detected. At times, abnormally large or tortuous veins indicating the presence
of a portosystemic shunt may be identified, although establishing their exact course may be
difficult. In some cases direct evidence of a shunt may not be apparent, but indirect
evidence (e.g., small liver or a decreased number of portal veins within the liver or both)
may be observed. 311,314
Hepatic Venous Congestion. Enlargement of the hepatic veins can be identified during
an ultrasonographic examination. In most cases, this is the result of hepatic venous
congestion secondary to cardiac disease such as right heart failure, pericardial disease, or
an intracardiac mass, resulting in caudal vena caval dilation and lack of respiratory periodicity.
The veins will be large and many smaller branches will be visible extending to the
margin of the liver. The evaluation is subjective, but in most cases an experienced ultrasonographer
has little difficulty recognizing the abnormality (Fig. 3-75). 6