What is carval liver shunt disease? Is it only in daushounds? Is it very common? Thanks:)

A liver shunt is a condition where one or more blood vessels that should deliver blood to the liver cells somehow bypasses the liver. Shunts can be outside the liver (extrahepatic) or within the liver (intrahepatic). They can be severe enough to cause symptoms in very young puppies, or so mild that they are never detected.
One of the liver's major jobs is to remove waste products from the blood, so if there is a large shunt or many smaller ones, the wastes just zip on by and never get removed. Eventually enough toxins can build up to cause jaundice, vomiting, neurologic problems and other symptoms.
Some shunts can be surgically corrected, although they generally require a surgical specialist, often at a university.
I'm not sure what "carval" is, unless it supposed to be "caval", which would refer to a shunt that comes directly off the vena cava--the body's largest vein.
They are not limited to Dachshunds, but they do seem to be more common in the smaller breeds.