Intrahepatic Shunts: Treatment Options and Critical Evaluation of Coil Embolization

Portosystemic shunts are anomalous blood vessels that result in an alteration of the normal flow of blood after delivery to the portal vein. When a portosystemic shunt (PSS) is present, blood that should normally be delivered to the liver via the portal vein is redirected, or “shunted”, into the systemic circulation. This shunting of blood prevents the liver from being able to perform several critical functions and results in the clinical signs that many of these patients manifest.

The clinical signs noted most commonly with PSS generally involve three major organ systems: the gastrointestinal tract, the urinary tract and the nervous system. Dogs and cats with PSS can be presented for evaluation secondary to non-descript signs such as vomiting, diarrhea, lethargy and anorexia, or more specific findings like seizures, “star-gazing”, disorientation, mental dullness or urolithiasis.

PSS can be either congenital or acquired. Congenital PSS are categorized into extrahepatic portosystemic shunts (EHPSS) and intrahepatic portosystemic shunts (IHPSS). EHPSS are shunts that are located outside of the hepatic parenchyma and cause blood to flow from the portal vein directly to the systemic circulation, into either the vena cava or the azygous vein. IHPSS are less common then EHPSS and are a communication between one of the major branches of the portal vein (left, right or central) and the vena cava via a hepatic vein. Acquired PSS generally occur from primary liver disorders such as hepatic cirrhosis, non- cirrhotic portal hypertension, and portal vein hypoplasia.

The diagnostic approach to the PSS patient can be extensive, although, characteristic changes on the bloodwork such as decreased liver function parameters (eg. glucose, albumin, cholesterol, BUN) and microcytic, normochromic nonregenerative anemia are often seen. In addition to a complete blood count and biochemical profile, the use of liver function testing (eg. serum bile acids and/or plasma ammonia levels) is often pursued. Diagnostic imaging is considered the gold-standard means of diagnosing PSS and various modalities including ultrasound, nuclear scintigraphy, computed tomography- angiography (CT-A) and magnetic resonance-angiography can all be pursued.  [...]