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Portosystemic shunts in veterinary medicine | VETgirl Veterinary Continuing Education Videos

In this VETgirl online veterinary CE video, we discuss portosystemic shunts (PSS) in dogs and cats in veterinary medicine. Portosystemic shunts (PSS)  are abnormal vessels, typically at the level of the portal system to the caudal vena cava or azygus vein, that allow normal portal blood draining from the gastrointestinal tract, pancreas, and spleen to flow directly into the systemic circulation. PSS can  be either extrahepatic or intrahepatic, but other underlying disease such as congenital portal vein hypoplasia or microvascular dysplasia can also occur, with the latter not being surgically correctible. With a PSS, the abnormal hepatic blood flow allows for toxic metabolites to travel systemically without being cleared by the liver first, resulting in hepatic encephalopathy.  Clinical signs of a PSS include a stunted nature, poor weight gain, poor recovery from anesthesia, hypersalivation (more in cats than dogs), star-gazing, blindness, ataxia, decreased mentation, seizures (commonly seen in cats!) and urinary obstruction (secondary to urate calculi). The diagnostic workup for PSS includes appropriately fasted pre- and post-prandial bile acids and ultrasound, although portograms and nuclear scintigraphy may sometimes be necessary. Treatment includes stabilization, surgical correction (if amenable), and treatment for hepatic encephalopathy and seizures.

In this VETgirl video,  a 9-month-old male neutered Domestic Short Hair presented with a history of seizures.  Diagnostics revealed elevated bile acids, and an extra-hepatic PSS and concurrent urate cystoliths on abdominal ultrasound. The patient was medically treated with antibiotics, lactulose (to decreases ammonia production and absorption), levetiracetam, and a low protein diet.  Tip:  Avoid phenobarbital in patients with shunts, as it will be very slowly metabolized and has a higher likelihood of reaching potentially toxic levels. Keep in mind that approximately 30% of patients can be successfully treated medically, but the median survival time is only about 2 years. Due to the severity of this cat’s symptoms despite medical management, surgical placement of an ameroid constrictor and a cystotomy were performed. Gradual occlusive devices, such as cellophane or ameroid constrictors, are the most common methods of surgical correction.  Although up to 3/4 of patients have successful outcomes following surgery, up to 1/4 of cases can have persistent shunting and neurologic symptoms, potentially resulting in death.

Post-operative management of a PSS includes fluid therapy (avoiding LRS if possible), blood glucose monitoring (and supplementation, if indicated), neurologic support (e.g., anticonvulsant therapy, hepatic encephalopathy treatment, etc.), and supportive care.  Post-operatively, this cat developed head tremors and subsequent seizures which were managed with pharmacological intervention. The prognosis for treatment of PSS is excellent, with 85% of dogs becoming clinically normal after 4 months (post-operatively). However, dogs with intrahepatic shunts have a higher surgical mortality rate. Owners should be warned that recurrence of clinical signs can occur in up to 50% of cases with shunts that achieve partial closure. In cats, the long term prognosis is poor in 25% of cats, particularly if uncontrollable seizures occur.

Reference:
1. Tobias KM. Portosystemic shunts. Accessed https://vetmed.illinois.edu/wp-content/uploads/2015/09/54.-Portosystemic-Shunts.pdf.

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