Portosystemic Shunt

*The Basics*
A porto-systemic shunt is an abnormal vessel that allows blood to bypass the liver. As a result the blood
is not cleansed by one of the bodies filters: the liver.


Mode of inheritance:

Age of onset:
Under one (1) year of age.

Portosystemic shunting is a term used to describe abnormal blood flow between the liver and the body.
The liver is responsible for detoxifying the body, metabolizing nutrients and eliminating drugs. When the
body’s blood flow bypasses the liver, as is the case with portosystemic shunts  (PSS), a multitude of signs
may appear.
There are two types of shunting: intra hepatic (the vein is within the liver) and extra hepatic (not
attached). Since congenital shunts are believed to be hereditary, dog breeders need to be aware of early
signs of liver disease so that potential carriers of the problem can be identified and eliminated from the
breeding program.

In an affected dog the liver is not getting an adequate blood supply and this causes the dog to be smaller
than normal. The liver is also not able to properly rid itself of all the toxins that it does manage to take in
through the capillary system. Protein is the major culprit. Dogs with liver shunt are not able to assimilate
the protein from food. Therefore most often the shunt is found because the dog suffers seizures from the
build-up of toxins.

Clinical signs of PSS are generally noticed before 1 year of age however, it is not uncommon for
symptoms to appear at around 2 years of age.

Warning signs are: head pressing, thin and/or poorly grown (small) dogs, depression, vomiting, ataxia,
aimless walking or compulsive pacing, circling, disorientation (weaving and bobbing) and apparent
blindness. Seizures are another possible sign of this problem. Uncharacteristic aggression can also be a
sign. All these symptoms may be multiple or singular to this disease.

Animals that are showing signs of liver disease should have a complete blood count, serum  chemistry
screen, and urinalysis performed. If the test results are suggestive of a liver disorder, the animal's bile
acids should be measured.

Bile acids are considered to be the most sensitive screening test for portosystemic shunts. Two (2) blood
samples are drawn, the first after a twelve (12) hour fast, the second sample is drawn 2 hours after a high
protein meal. Elevation of bile acids (especially the second sample) is highly suggestive of a
portosystemic shunt (rather than any other cause of liver disease). These patients should have the
diagnosis of PSS confirmed.

Diagnostic tests include radiographs, ultrasonography and intravenous portovenography.
Portovenography involves anesthetizing the patient, injecting radio opaque dye intravenously, and taking
radiographs of the liver as the dye is circulating through the liver vasculature.

Treatment of choice is surgery to tie off the abnormal vessel or to place a metal band around it so it is
eventually occluded.( Ameroid Constrictor)

Prolonged recovery after anesthesia, or excessive sedation after administration of tranquilizer or
anticonvulsant., anorexia, lethargy, circling, pacing, behavioral changes, blindness, seizures, vomiting
(intermittent), diarrhea (intermittent), stunted growth or failure to gain weight.


Portosystemic Shunts
Info and animated diagram

The University of Tennesee Portosystemic Shunts


Dr. Karen Tobias

Liver Shunt Info

Liver Disease Signs Symptoms and Diagnosis

Blood Chemistry Levels Normal Ranges for Dogs

Understanding your Dogs Blood Work

The Ins and Outs of Pedigree Analysis, Genetic Diversity, and Genetic Disease Control by Jerold Bell,
DVM (Director of the Clinical Veterinary Genetics course for Tufts University School of Veterinary
Medicine and National Project Administrator for numerous genetic disease control programs of pure-
bred dogs).
The Ins and Outs of Pedigree Analysis, Genetic Diversity, and Genetic Disease Control


Control of Genetic Disease by Dr. George A. Padgett, DVM (Veterinary Pathologist at Michigan
State University with special interest in canine genetics and what role breed clubs play in the control of
the genetic diseases in their particular breed).
The Biewer has the potential to have the same genetic defects as the Yorkshire Terrier.  There
has been now more than 5 documented Liver Shunt Biewers imported into America from
Mind you... that is the Liver Shunt Biewers that we KNOW OF.     

As in any breed the need for strict breeding practices is paramount.  Honesty, integrity  and
ethical breeding practices ensures the health and longevity of our beloved breeds.  

One of my very good friends acquired one of these liver shunt babies from a breeder  in
Germany that promised her 2  healthy Biewers.  

All reputable breeders should have their vets preform a Liver profile done.   Good breeders will
supply buyers with proof of those tests.  The heartache of having a Liver Shunt baby will break
your heart not to mention your saving account.   A simple blood test given to your pup before
you buy it will give you peace of mind.  Make sure you ask for it!  Bile Acid tests at the age of
12 weeks are not definitive....Liver enzymes will show a problem enough that a breeder can
hold that pup and Bile Acid test when age appropriate.

Below you will see very graphic pictures of a precious Biewer pup having a liver shunt surgery.  
Sadly, YES... this is my friends supposedly healthy pup.  

Breeders ....
Test all pups and breeding pairs.  If you have a liver shunt pup don't hide it under the rug.  Be
forthcoming with information so that we can stop the lines that carry the gene.  Any breeder
can have a Liver Shunt pup.  It's what we do afterwards that counts.  
We are the protectors of the breed... it is up to US!
So far Cattia has done wonderfully and has turned into a beautiful girl thanks
to my friend having saved her life.  Isn't it a shame her breeder did not spend
the $100.00 on the Liver enzyme test?  Instead he sent her here sick and dying.   
My friends dreams for her are gone... as well as a lot of her savings.  She will
never be the lovely show girl she was meant to be.  She lives in the arms of a
very proud and greatful mom!  
This is Cattia...
Below there is a link to her and
her breeders  story... read it!
Dr. Sharon Center’s talk on PSVA and MVD
February, 2007

Current information regarding the heritability of PSVA and MVD substantiated that they
are related abnormalities, they are congenital, and are consistent with an ancient genetic
mutation that occurred as small dog breeds were evolving (because so many breeds are

The first thing to consider is that we are in the process of discovering the underlying genetic
cause and hoping to develop a useful test to help eliminate these traits:  Don’t do anything

Some dogs with PSVA may drink a lot of water, eat abnormal substances, drool, do head
pressing, have a cholesterol less than 150 mg/dl and microcytic (small red blood cells).
However, not all dogs with PSVA or MVD have symptoms or are ill; in fact up to 20% of
PSVA dogs may be asymptomatic which has resulted in some of these dogs being used for

Unlike dogs with PSVA, dogs with MVD usually do not manifest clinical signs, are not ill,
and do not require medical or dietary treatments.

The only test that is reliable for PSVA screening is bile acid testing because ammonia is so
labile. -Blood ammonia is not a good or reliable indicator of PSVA or MVD (lots of false
positives and the blood ammonia samples are very unstable). Ammonia measurements must
be evaluated immediately, cannot be frozen, and environmental variables can vastly alter
results.  Ammonia measurements cannot be done using samples mailed to a laboratory.  
Ammonia challenge with administration of ammonium chloride given orally or per rectum
optimizes the use of ammonia as a diagnostic test for shunting but can cause
encephalopathic signs.  In contrast, serum bile acids are stable, can be mailed, can be
measured after extended refrigeration or sample freezing.  A recent veterinary clinical
publication touted the use of ammonia to detect shunts over bile acids; the study was biased
by several confounding factors and compared ammonia concentrations only to fasting bile
acids: DO NOT USE SINGLE BILE ACID VALUES to rule out shunting- that has
long been established by rigorous investigation in our hospital and published in 5 peer
reviewed scientific manuscripts.

Serum bile acids should be collected Before and 2-hours After a meal (this serves as a
provocative challenge initiating bile acid release from the gallbladder, intestinal
reabsorption, passage into the portal vein to the liver, and rapid liver extraction from the
portal blood).  The term Postprandial refers to the after meal sample.  Dogs DO NOTneed
to be fasted for 12-hours to conduct this test.  The important issue is to test BEFORE and 2-
Hrs after FEEDING to fully evaluate the dogs ability to extract bile acids from the portal
circulation.  Spilling of portal blood contents into the systemic blood is reflected by finding
high Serum Bile Acid values > 25 umol/L in a sample collected from a leg vein or jugular

About 15-20% of dogs have a higher fasting than post-prandial bile acid values so using a
random bile acid sample or a single bile acid sample is not optimal. ALWAYS: USE

The cut-off for abnormal results used by Dr. Center fasting AND for Postpprandial values
is greater than or equal to 25 micromole/L (normal dogs do not have bile acid values > 15
micromole/L at either interval).  To avoid calling normal outliers abnormal, an indisputable
cutoff was mathematically determined based on samples from hundreds of healthy dogs and
dogs with liver disease in Dr. Center’s laboratory.

Both PSVA and MVD dogs have increased serum bile acid values; BUT you can’t tell if a
dog has PSVA or MVD based on bile acid results alone.  It is true that dogs with PSVA
often have at least one bile acid value > 200 umol/L, but not always.  Some MVD dogs can
develop bile acids at high as 200 umol/L also.

The bile acid test is very reliable but the red blood cells MUST be separated from plasma
(the clear part of blood) before they are sent to lab for analysis (centrifuged or spun to allow
plasma separation from blood cells).  Results can be falsely abnormal if the bile acid samples
are lipemic (lots of fat IF the fat is not adequately removed by the laboratory analyzing the
sample) or if hemolysis (burst red blood cells, makes the plasma red) occurs.  The red color
interferes with the color of the end point dye in the bile acid test.  A clinician can tell if the
sample is hemolyzed when they centrifuge the sample to separate the red blood cells from
the plasma.  If it is hemolyzed they should collect another sample.  Drawing blood with a
vacutainer needle into a vacutainer (suction of the tube facilitates the collection) may be too
traumatic for some red blood cells augmenting hemolysis.  Using a syringe and needle or
syringe and butterfly needle appears to collect the best samples.  After the blood is collected,
the needle should be removed from the syringe and the top removed from the vacutainer so
that the blood may be gently transferred to the vial.  Results of the bile acid test should
state if the samples were lipemic or if hemolysis occurred.  In this case, the tests should be

Most dogs with PSVA will have Ammonia Biurate Crystals in their urine detected if 3
urine samples collected at different intervals are evaluated.  Urine from these dogs has a
peculiar light orange-brown color observed if the dogs urinate on a white surface.  The color
is derived from the gold-brown color of the tiny ammonium biurate crystals. A laboratory
technician can check for these crystals on a sample of urine.  MVD dogs will not have Urine-
Ammonia Biurate Crystalluria so when the crystals are found you likely have a shunt in a
Cairn Terrier.  Unfortunately, any cause of severe liver disease can lead to the development
of multiple portosystemic shunts and ammonium biurate crystalluria.  Thus, in older dogs
where finding the crystals is a new event, we will need to make sure what the underlying
cause is.  Ultrasound and liver biopsy may be necessary.

If a dog has elevated bile acid values (either fasting or postprandial), determination of
Protein C activity can help differentiate between PSVA and MVD (local vet can collect a
citrate anticoagulated blood sample, separate the plasma for mailing, and send it to Cornell
for analysis).  This sample collected in a special citrate anticoagulated vial.  Specifics of the
test can be clarified by calling the Cornell Diagnostic Laboratory at 607-253-3900; the test is
conducted by the Comparative Hematology / Coagulation Laboratory [Dr. Marjory Brooks].

MVD dogs usually are not ill and do not require a special diet.  Rarely, some of these dogs
have had a problem with drug metabolism (e.g. antihistamines, certain anesthetics)

Pursuing an asymptomatic dog with high bile acids and normal Protein C can result in
costly and invasive testing; thus some MVD dogs are subjected to rigorous evaluations that
may not be practically useful.  Most of these dogs require no treatment yet often, a diet
modification and even antioxidants are sometimes recommended.  In most cases, these are
unnecessary for the MVD dog based on Dr. Center’s extensive experience with MVD.

In the very large pedigree of Cairn Terrier’s studied so far (>600 dogs) there is a 31%
affectation rate of vascular malformations INCLUDING dogs with PSVA and dogs with
MVD.  Our data and linkage analyses support that these disorders represent two
manifestations of the same genetic trait.

PSVA dogs should not be bred until we gather more information on the genetic basis of the
disorder.  We do not know yet whether MVD represents a heterozygous situation or just a
less severe trait manifestation.  It is too early to start culling all dogs with high bile acids-
read the next paragraph to convince yourself why this may be ineffectual:.

We know that some parents with normal bile acids have produced dogs with PSVA and
MVD. Since we believe that PSVA and MVD represent disorders of angiogenesis, it is
quite possible that not all dogs carrying the trait will have liver or portal vein involvement.  
Consider for example, that we have documented dogs with vascular malformations between
the spleen and vena cava that have not influenced portal venous blood flow and thus did not
cause high bile acid values.  So, the trait may exist in some dogs with normal bile acid
values.  We also have some evidence that we may only see a subset of dogs with PSVA; we
suspect there are embryonic deaths in severely affected dogs likely related to abnormal
vasculature involving the placenta.  

At present we recommend that all Cairn puppies undergo paired bile acid tests before they
are adopted into homes (15 weeks or so).  Why? Because you do not want a veterinarian to
surprisingly find high bile acids when a dog is presented for illness.  This results in
aggressive testing that may include an expensive abdominal ultrasound and even a liver
biopsy in a dog with MVD- consider for example a dog presented for vomiting after eating
garbage.  A high bile acid test would implicate the liver as being severely affected, and the
clinician would be obligated to inform the client that the liver should be investigated.  If they
already knew the dog had high bile acids as a pup, consistent with MVD, then the medical
investigations would be judiciously focused on the vomiting.
Liver Portosytemic Vascular Anomaly (PSVA)
Microvascular Dyplasia (MVD)
This new information was added on
February 21, 2008