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PEER REVIEWED 64 JULY/AUGUST 2018 seen in dogs than in cats. A congenital shunt can be intrahepatic or extrahepatic. A complete description and review of this material are beyond the scope of this article, so only the essentials are discussed here. Intrahepatic congenital PSSs occur predominantly in large-breed dogs and are often attributable to a patent ductus venosus, originating from the intrahepatic left division of the portal vein and connecting to the left hepatic vein. 16,17 If originating from the right branch of the portal vein, these shunts drain directly into the caudal vena cava. Extrahepatic congenital PSSs in dogs are connections between the portal system (either the portal vein or any of its afferents, such as the left gastric vein, splenic vein, or gastroduodenal vein) and the systemic venous circulation (either the caudal vena cava or the azygos vein). Cats may have intrahepatic or extrahepatic shunts; the morphology of extrahepatic shunts varies widely depending on their origin, course, and termination. 18,19 FIGURE 7. Short-axis view of the portal vein, represented by the anechoic structure in the near field, and caudal vena cava, represented by the anechoic structure in the far field, at the level of the porta hepatis in an adult dog with hypercoagulopathy (A). Note the ovoid, echogenic structure in the lumen of the portal vein (A) and the disrupted color flow Doppler signal with a filling defect within the lumen corresponding to a portal vein thrombus (B). A B FIGURE 8. Short-axis view of the liver (A) without and (B) with color Doppler at the level of the portal vein and caudal vena cava in a 2-month-old mixed-breed puppy with a portocaval intrahepatic shunt. Note the turbulent blood flow, denoted by the aliasing artifact, in the lumen of the anomalous shunting vessel and the portal vein. This turbulence is consistent with an extrahepatic portocaval shunt. A B Congenital PSSs are single, large, anomalous connections between the portal and systemic veins that allow portal blood from the gastrointestinal tract to bypass the liver.

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