Soft Tissue Surgery
Learn more about portosystemic shunts below.
Portosystemic shunts (PSS) are abnormal vessels that allow normal portal blood drainage from the stomach, intestines, pancreas, and spleen to bypass the liver and flow directly into the systemic circulation. Depending on where the shunting vessels occur, congenital shunts can be classified into two main categories: intrahepatic and extrahepatic. Intrahepatic portosystemic shunts typically occur within the liver of large breed dogs. Extrahepatic shunts, however, are more common in the livers of small breed dogs.
Signs and consequences of PSS
When portal blood bypasses the liver, toxins that the liver would otherwise neutralize are circulated throughout the body. These toxins can then negatively affect many of the body’s systems, such as the central nervous system. Neurologic dysfunction associated with PSS can range in severity from extreme sedation to blindness, and uncontrollable seizures may occur in affected dogs, also known as hepatic encephalopathy. These signs are often seen following a high-protein meal. Urinary disorders can also occur from urinary stone formation.
Diagnosis of PSS:
PSS in dogs often produces blood work that is typically characteristic of a poorly functioning liver. Noticeably, there are low levels of glucose, protein, and blood clotting factors which are all produced in the liver. Evaluation of urine often shows typical ammonium biurate crystals. Liver function testing (measuring bile acid levels before and after eating) can also be beneficial. Portosystemic shunts can be found during abdominal ultrasounds. In the hands of an experienced ultrasonographer, ultrasound with color flow doppler is diagnostic of a shunt 95% of the time.
Portosystemic Shunt Treatment
Though it is possible to manage shunts medically, the prognosis is guarded, with a median survival of approximately 2 years without surgical correction. Surgical closure of the shunt is the recommended go-to treatment since it may allow for an average life span without requiring further treatment. Since most dogs with PSS have small livers that are unable to handle the normal portal blood flow, shunt attenuation must be performed over time to mitigate fatal portal hypertension (increased blood pressure within the portal system). Multiple surgical techniques exist to allow for gradual occlusion of a PSS and are often dependent on the type (intrahepatic or extrahepatic) and size of the shunting vessel. The prognosis for surgical correction of PSS varies depending on the type of shunt, animal age, and clinical signs before shunt occlusion. In general, a good-to-excellent outcome can be achieved in 80-95% of patients. Potential postoperative complications include hemorrhage, portal hypertension, the development of multiple acquired shunts, seizures, and possible death.