Portosystemic shunts (PSS) are anomalous 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. Congenital shunts can typically be divided into two main categories (intrahepatic and extrahepatic) based on where the shunting vessel occurs. Intrahepatic portosystemic shunts occur within the liver and are typically found in large breed dogs. Extrahepatic shunts occur outside the liver and are most common in small breeds.
Signs and consequences of PSS
When portal blood bypasses the liver, toxins that are normally deactivated by the liver are circulated to the rest of the body, the results may affect many body systems, most seriously the nervous system. Due to several factors associated with PSS, neurologic dysfunction ranging from severe sedation to blindness and uncontrollable seizures may occur in affected dogs. This is referred to 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:
Dogs with PSS often have characteristic blood work typical of a small poorly functioning liver. Glucose, protein and blood clotting factors (all produced in the liver) are often low. Evaluation of urine often shows typical ammonium biurate crystals. Liver function testing (measuring bile acid levels before and after eating) is very helpful. Portosystemic shunts can often be found during an abdominal ultrasound. 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, without surgical correction, the prognosis is guarded with a median survival of approximately 2 years. Surgical closure of the shunt is the treatment of choice and may allow for a normal life span without the need for further treatment. Since most dogs with PSS have small livers unable to handle the normal portal blood flow, shunt attenuation must be performed gradually to prevent 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, age of animal and clinical signs prior to 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.