shunts cause serious and sometimes fatal outcomes in dogs. A liver
shunt, or a portosystemic shunt, is a normal fetal blood vessel that
in the womb bypasses liver tissue, allowing the mother's system to
filter out toxins for the developing baby. In some animals however,
the shunt remains open after the animal is born compromising its
liver function, slowing growth, and eventually resulting in death of
many affected animals. Congenital portosystemic shunts may be
repaired with traditional surgical approaches but a technique
developed at the University of Tennessee several years ago implants
an ameroid constrictor, a tiny C-shaped piece of metal ring. The
constrictor fits around the shunt causing it to slowly shut down
over several weeks. Dogs receiving this method of surgical repair
generally have a shorter surgery and fewer postoperative
complications than traditional methods.
What is a
In animals with a
portosystemic shunt (PPS) there is abnormal blood flow in the liver.
Blood should flow from the digestive tract to the liver via the
portal system into the blood vessels of the liver and then to the
caudal vena cava which is the large blood vessel carrying blood back
to the heart. In a portosystemic shunt, as the name implies,
portal blood by-passes the liver and goes directly to the
systemic venous circulation (caudal vena cava). One important
function of the liver is to clear toxins, many of which are
by-products of protein digestion, from the blood. In PSS these
toxins are not cleared, and circulate in the body. This causes the
clinical signs associated with PSS, many of which are neurological.
The complex of neurological and behavioral signs caused by liver
dysfunction is called hepatic encephalopathy.
shunts may be acquired secondary to another disease, or they may be
congenital, that is the animal is born with a shunt. A congenital
shunt usually occurs as a single abnormal blood vessel that is a
remnant of normal embryonic development. These shunts are defined as
intra-hepatic or extra-hepatic depending on the location of the
blood vessel in relation to the liver.
Most animals with
congenital portosystemic shunts show clinical signs before 6 months
of age. Where signs are subtle, the condition may not be diagnosed
until much later.
How are congenital
portosystemic shunts inherited?
The mode of
inheritance is not known.
What breeds are
affected by congenital portosystemic shunts?
There is a breed
predisposition to congenital PSS in the following breeds:
small breeds, especially the Yorkshire Terrier, Miniature Schnauzer
and less commonly, Cairn Terriers and Maltese.
large and giant breeds, especially the Irish Wolfhound and less
commonly, Australian Cattle Dogs, Golden Retrievers, and Labrador
Retrievers. Approximately one third of large dogs with shunts have
For many breeds and
many disorders the studies to determine the mode of inheritance or
the frequency in the breed have not been carried out or are
inconclusive. We have listed breeds for which there is a general
consensus among those investigating in this field and among
veterinary practitioners that the condition is significant in this
What does a
congenital portosystemic shunt mean to your dog and you?
If your dog has a
congenital portosystemic shunt you will likely see signs of this
while he or she is a young puppy. These signs are generally
associated with the central nervous system, the gastrointestinal
tract or the urinary tract. Most consistently there are signs of
hepatic encephalopathy, neurological and behavioral evidence of
diffuse brain disease due to liver dysfunction. These signs can be
quite vague and may include loss of appetite, depression, lethargy,
weakness, poor balance, disorientation, blindness, seizures and
coma. The signs may wax and wane and may worsen after eating a
protein rich meal.
Your pup may appear to be growing very slowly. Other non-specific
gastrointestinal signs can include intermittent loss of appetite,
vomiting and diarrhea.
the liver to clear ammonia means that there will be increased
excretion in the urine. This commonly leads to urolithiasis -kidney,
bladder or urethral calculi or stones due to the build up of mineral
salts. Your dog may have blood in the urine, or difficulty or pain
sign of PSS in a dog may be a prolonged recovery from anesthesia or
excessive sedation after treatment with some medications. This
occurs because the drugs are not metabolized as they would normally
be by the liver, but instead are re-circulated in the body.
How is a
congenital portosystemic shunt diagnosed?
diagnosis of congenital PSS is suspected based on the history,
clinical signs and laboratory features. Typically an affected dog is
young, of a breed with a predisposition for PSS, with clinical
signs and laboratory findings relating to liver dysfunction. A
special radiographic tool, contrast portal radiography, is the best
way to confirm the diagnosis. Contrast dye is injected into one of
the blood vessels going into the liver. In a normal liver, the
contrast material disperses into the many blood vessels in the
liver, but in congenital PSS, a large portion of the contrast
bypasses those vessels and goes directly to the caudal vena cava,
the large blood vessel that carries blood to the heart. Contrast
radiography also helps in assessing the chances of successfully
tying off the shunt surgically. The more contrast that is apparent
in the liver, the higher the likelihood of success. Contrast
radiography will also identify whether the shunt is intra- or
How is a
congenital portosystemic shunt treated?
Many of the
clinical signs associated with PSS can be improved by medical
management. Since circulating ammonia is one of the main causes of
hepatic encephalopathy, and ammonia is derived from eating meat, a
low-protein diet is an essential component of medical therapy for
treatment will improve the clinical signs temporarily, surgery to
tie off the shunt is required to correct the condition for the long
term. Ligation (tying off) of the shunt may be partial or complete.
An intra-hepatic shunt is generally technically more difficult to
correct than an extra-hepatic one. Your veterinarian may suggest
your dog go to a referral centre, both because the procedure is best
performed by an experienced surgeon and because close monitoring is
required post-operatively to watch for signs of portal hypertension.
This potentially serious complication may develop within 24 hours of
surgery, due to the increase in blood flow in the liver once the
blood is no longer moving through the shunt.
extra-hepatic shunts, there is a very good prognosis for a normal
life for your dog after surgery. Dogs with intra-hepatic shunts may
still have some biochemical abnormalities following surgery but in
general, clinically, show much improvement.
individuals and their parents should not be used for breeding.
Siblings should only be used after careful screening. If any
affected offspring are born, breeding of the parents should be