This
much-discussed disorder is most
commonly the result of improper
fetal development of the
circulatory system. To thoroughly
understand liver shunts, it is
important to have an understanding
of the development of blood
vessels in the fetus. The fetus,
through the placenta, umbilical
vein and artery, is connected to
the mother's circulatory system
(bloodstream). Therefore, the
liquid portion of the blood of the
fetus can move into the mother's
bloodstream, but the cells cannot.
The mother's
liver then performs the
important liver functions, such as
eliminating wastes, for the fetus.
The mother's liver is necessary
for this, since the fetal liver is
just developing and is not yet
capable of many functions
including removing metabolic
wastes from the fetal bloodstream,
storing minerals, and enzyme
production. Because the fetal
liver is underdeveloped, the fetus
possesses blood vessels which
transport blood around the
developing liver rather than to
and through it. This is necessary,
since the small developing fetal
liver cannot filter or handle the
full quantity of blood that needs
to be filtered. When the fetus is
born, the placenta, umbilical vein
and artery (jointly referred to as
the umbilical cord) are severed
and are no longer functional. Once
the umbilical cord is cut at
birth, there is no longer this
connection between the mother and
the just-born puppy. At this
point, the puppy must rely on his
own liver functions and not that
of his mother.
At or
about the time of birthing
(whelping), the blood vessels
within the fetus, which allowed
blood to bypass the developing
fetal liver, must close. Once
these vessels close, the puppy's
blood is forced to pass through
the puppy's now developed liver.
If these fetal vessels fail to
close, then blood is allowed to
abnormally be shunted around the
liver, hence the name liver shunt.
When blood is shunted around the
liver rather than to and through
it, the liver is not able to
filter all of the blood, and
therefore, toxic metabolic wastes
such as ammonia are not adequately
removed from the bloodstream. The
degree to which blood is shunted
around the liver is dependent on
the extent to which shunting
vessels persist. Liver shunts may
be large allowing much blood to
bypass the liver, or they may be
partially closed allowing only
small amounts of blood to shunt
around the liver. The extent of
blood shunting varies with every
dog.
What are the
symptoms?
The
symptoms of liver shunts vary and
are directly related to the extent
of blood shunting. If the liver is
receiving and processing 95
percent of the puppy's blood, the
symptoms may be few, if any. More
severe shunts are life threatening
with many symptoms. Symptoms may
be evident in these puppies at
only a few weeks of age and may
include low growth rates,
vomiting, diarrhea, constipation,
salivation, increased urination,
seizures, and death. Dogs with
less severe liver shunts may not
exhibit any clinical signs until
the puppy is much older, even up
to a year of age.
What are the
risks?
All liver
shunts, whether mild or severe,
are considered serious and life
threatening. Even mild liver
shunts generally exhibit greater
symptoms as the puppy increases in
body size. The larger the puppy
the more metabolic wastes
produced, and therefore, the more
the liver is needed. Most affected
dogs will not live a normal life
expectancy unless the abnormality
is corrected.
What is the
management?
Management techniques for liver
shunts have improved. The best and
preferred treatment is to identify
the abnormal blood vessels and
surgically close them, eliminating
the shunt. This will require
sophisticated testing and may
include radiographs (x-rays),
laboratory blood analysis,
ultrasound,
and intravenous
dye studies. The expense and
results are variable depending on
the degree of shunting, age, and
symptoms. In addition to surgery,
alterations in diet, and
administration of medications are
often beneficial. Restricted
protein diets help reduce the
production of the toxic waste,
ammonia, and will therefore help
lessen the need for liver
detoxification. Owners and
veterinarians should thoroughly
discuss the seriousness, expense,
and expected outcome associated
with the management of all
individuals suspected of having a
liver shunt.
