Liver shunts in Norwich terriers
A liver shunt is a blood vessel that carries blood around
the liver instead of through the liver. Thus blood
that would normally be filtered by the liver does not
get filtered which allows the build up of toxins in the
blood stream. Liver shunts are a polygenetic disease
for which we have no DNA test (). It seems
to have two forms in small dogs, which are suspected of
being genetically related - a mild form called portal vein
hypoplasia or microvasular disease (PVH-MVD), and a severe
form called a portosystemic shunt (PSS). It is thought that
the incidence of PVH-MVD is much higher that PSS, since most
dogs with PVH-MVD never show any signs and hence never
have their liver tested.
In a population of dogs seen at the UC-Davis Vet Hospital,
Norwich terriers were the second most likely breed to
have a liver shunt ().
Portal Vein Hypoplasia
An older name for portal vein hypoplasia (PVH) is
microvascular disease (MVD). In this form, very small
shunts are found throughout the liver. A PVH-MVD dog
usually does not show any signs. A bile-acid test (liver
function test) usually shows only mildly abnormal values.
A special "Protein C" blood test - done only at Cornell
- can be used to differentiate between PVH-MVD and PSS
(). Most dogs with PVH-MVD live a normal life without
any complications from PVH-MVD; however they may have
trouble metabolizing drugs that require rapid delivery
and extraction in the liver ().
A portosystemic shunt (PSS) is sometimes called a
portosystemic vascular anomoly (PSVA). In small dogs
this is a shunt outside the liver (extra-hepatic shunt).
In large dogs, it is typically a shunt inside the liver
(intra-hepatic shunt). This is most frequently found when
a dog shows signs such as lethargy, a routine blood test
points to the liver, then a bile-acid test (liver function
test) shows very high abnormal values. Some dogs survive
without surgery, but most need surgery.
Liver testing is recommended for all Norwich
Dr. Sharon Center - one the world's leading researchers
on canine liver shunts - recommends bile-acid testing
of all puppies in breeds affected with liver shunts.
(). You can do a bile-acid test on a dog as young
as four months old; earlier can give abnormal readings.
The purpose is to know a dog's liver status in case of some
medical problem later in life. You do not want a vet to be
surprised by abnormal bile acids results, which might make
the vet suspect and investigate the liver ... rather than
concentrating on the actual signs of the medical problem.
A bile-acid test is nothing more that a blood draw
("preprandial" i.e., fasting) followed by a meal, then two
hours later another blood draw ("postprandial"). A lab can
then analyze the blood and report on the bile acid levels
(which indicate liver function).
A compromised liver causes anesthesia risk; some Norwich
have died from anesthesia during routine dental exams.
Possibly a liver shunt was the cause of death of some of
these cases. Since the purpose of the liver is to filter
out toxins from the blood, if the liver is not working
correctly, it is possible for the dog to have seizures.
Idiopothic seizures (seizures of unknown origin) have been
reported in Norwich terriers; possibly a liver shunt was
the cause of some of these cases. Also "fading puppies"
have been noticed by Norwich breeders, again it is possible
that the cause is a liver shunt.
For further introductory information see references ,
, and . For more in-depth information see references
, , , ,  and .
There is a high message volume Liver_Shunt_And_MVD_Support yahoogroup.
Last updated 10 August 2016.
 Complex disease and phenotype mapping in the domestic dog Hayward et al., Nature Communications, 22 January 2016.
 Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995-2010), Bellumori et al., JAVMA Vol 242 No 11, June 2013.
 Cornell Comparative Coagulation Protein C Web Site.
 Help! My Dog was Diagnosed with a Liver Problem!, Dr. Karen Tobias, University of Tennessee College of Veterinary Medicine.
 Portosystemic Vascular Malformations in Small Animals, Merck Vet Manual, article by Dr. Sharon Center, last updated May 2015.
 Portosystemic Shunts, AKC/CHF web page.
 Hepatic Vascular Malformations In Small Dog Breeds: What the Textbooks Don't Tell You, Dr. Sharon Center, 2009.
 Medical Management: Portosystemic Vascular Anamalies (PSVA), Dr. Sharon Center, 2011.
 Diagnostic Approach: Portosystemic Vascular Anomalies (PSVA), Dr. Sharon Center, 2011.
 Inherited liver shunts in dogs elucidate pathways regulating embryonic development and clinical disorders of the portal vein, Frank G. van Steenbeek et al., Mamm Genome. 2012 Feb; 23(1-2): 76–84.
 Aberrant gene expression in dogs with portosystemic shunts, Frank G. van Steenbeek et al., Plos One, 25 February 2013.
 The inheritance of extra-hepatic portosystemic shunts and elevated bile acid concentrations in Maltese dogs, C. A. O'Leary et al., Journal of Small Animal Practice, 55: 14–21, January 2014.