Congenital Portosystemic Shunts in Dogs and Cats: Classification, Pathophysiology, Clinical Presentation and Diagnosis

SIMPLE SUMMARY: Congenital portosystemic shunts (CPSS) are abnormal vessels allowing communication between the splanchnic and systemic circulations. They are either extrahepatic (ECPSS) or intrahepatic (ICPSS), single or multiple. ECPSS is most commonly diagnosed in small and toy-breed dogs and cats, while ICPSS is most commonly seen in large-breed dogs. The clinical signs associated with CPSS, are due to hepatic encephalopathy (HE), and commonly involve the nervous system, gastrointestinal tract, and urinary tract. Neurological signs include depression, listlessness, ataxia, pacing, circling, head pressing, cortical blindness, seizures, and coma. Gastrointestinal signs, such as vomiting, diarrhea, anorexia, and ptyalism, occur in about 30% of dogs with CPSS. In cats with CPSS, ptyalism is a very common clinical sign, present in the vast majority of cases. Urinary signs include dysuria, stranguria, pollakiuria, and haematuria, and are associated with ammonium urate uroliths. The most common clinical pathology findings in dogs and cats with CPSS are mild to moderate microcytic normochromic nonregenerative anemia, elevated liver enzymes activities, hypoalbuminemia, decreased blood urea nitrogen (BUN), hypocholesterolemia, and hypoglycemia. Coagulation times are frequently found prolonged in affected dogs, but usually, they are not clinically significant. Urinalysis abnormalities include decreased urine specific gravity and ammonium biurate crystalluria. Liver function is evaluated by measurement of serum bile acids (BA) and fasting plasma ammonia (FA) concentrations. Both pre- and postprandial serum BA should be evaluated. Liver biopsy results include atrophy, decreased numbers of portal tributaries, and proliferation of arterioles and bile ductules. Survey radiographs are of limited value in the diagnosis of CPSS. Ultrasound is widely used for CPSS diagnosis due to its availability, but it is an operator-dependent technique. Computed tomographic angiography (CTA) has become the gold-standard technique for CPSS detection and characterization, as it is non-invasive, more accurate than ultrasound, and offers great surgical planning. ABSTRACT: Congenital portosystemic shunts (CPSS) are abnormal vascular communications between the portal and the systemic circulation, bypassing the hepatic parenchyma and resulting in liver hypoplasia and hepatic insufficiency. Such connections develop in utero and persist postnatally. CPSS are among the two most common congenital vascular anomalies of the liver in small animals, along with primary hypoplasia of the portal vein without portal hypertension (PHPV without PH). CPSS can be extrahepatic (ECPSS), most commonly diagnosed in small and toy breed dogs and cats, or intrahepatic (ICPSS), most commonly seen in large breed dogs. Single ECPSS is the most common type encountered in both dogs and cats. Clinical signs of CPSS are non-specific and may wax and wane, while laboratory findings can raise clinical suspicion for CPSS, but they are also not specific. Definitive diagnosis will be established by evaluation of liver function tests, such as determination of fasting plasma ammonia (FA) levels, and pre- and postprandial serum bile acids concentrations, and diagnostic imaging. The purpose of this article is to review the definition, classification, pathogenesis, clinical presentation, and diagnosis of CPSS in dogs and cats, highlighted by the authors’ clinical experience.