Dr. Arnold Plotnick is the found-
er of Manhattan Cat Specialists,
a feline-exclusive veterinary
practice on Manhattan’s upper
west side. He is also an author
of The Original Cat Fancy Cat Bible. Dr.
Plotnick is a frequent contributor to feline
publications and websites, including his
own blog, Cat Man Do. He lives in New
York City with his cats, Mittens and Glitter.
Here are the basics
The spleen is a dark red organ that
looks like a giant tongue. It is longer than it is wide and is covered
by a thick fibrous capsule. Located
near the stomach, it’s on the left
side of the body. However, the
exact location of the spleen isn’t
fixed. Depending on its size and
shape and the size of the surrounding organs, the spleen can migrate
around the abdomen and visit the
right side of the body.
The spleen performs a surprisingly large number of functions.
Here are the four most important:
Production of red blood cells
The bone marrow is the primary site
of red blood cell production, and
the spleen is the next major site.
Storage of red blood cells.
The spleen holds a fair amount of
blood. If the body was suddenly in
need of extra red blood cells, the
spleen can contract, releasing red
blood cells into the bloodstream.
Filtration. Think of the spleen
as a giant filter that traps and
removes old or abnormal blood
cells from the circulation.
Immunity. The spleen traps
bacteria, foreign proteins, and other
microbes and presents them to
cells in the immune system, so an
immune response can be initiated.
With all of these important roles,
you’d think the spleen would be
essential for life. Surprisingly, it can be
surgically removed if necessary, and
most animals will be fine. However,
it’s better to have one than to not.
When things go amiss
Disorders of the spleen are much
more common in dogs than in cats.
Splenic disorders can be generally
categorized as either primary or
secondary. A primary splenic disorder is one in which the spleen itself
is the site of the illness. The spleen
can also be affected secondarily by
a systemic disease that is occurring
somewhere else in the body.
When things go awry, spleen-
wise, the spleen usually grows
bigger. Enlargement of the spleen
is called splenomegaly. This is not
something a cat owner would be
able to detect. Splenomegaly is
usually found during the physical
examination, at the part of the
exam where the veterinarian care-
fully presses on the abdomen to
feel the internal organs.
Once splenomegaly is discovered on examination, your veterinarian will recommend diagnostic
tests to help determine the cause.
Blood tests and X-rays may provide
important information. Abdominal
ultrasound, however, is an excellent,
non-invasive procedure to distinguish localized versus generalized
splenomegaly and to further define
In most cases, however, a definitive diagnosis can only be achieved
by obtaining a sample of cells from
the spleen for analysis. The sample
is usually acquired via fine needle
aspiration, a procedure in which
a needle, attached to a syringe, is
gently inserted into the spleen.
Material is then aspirated into the
hub of the needle, and the con-
tents sprayed onto a microscope
slide. The slide is evaluated by a
clinical pathologist. If this does not
yield a diagnosis, abdominal explor-
atory surgery may be warranted.
Sadly, infiltration of the spleen
with cancer cells is the most com-
mon cause of splenomegaly in cats.
The most common cancer affect-
ing the feline spleen is mast cell
tumor. Hemangiosarcoma (a very
bad tumor; my cat Crispy died from
this) is the next most common, fol-
lowed by lymphosarcoma.
Fortunately, disorders of the
spleen are much less common in
cats, compared to dogs. When they
do occur, the prognosis will vary,
depending on the cause.
Splenomegaly occurs in two
forms: localized and generalized.
Where one focal area of the
spleen is enlarged, called a “splen-
ic mass.” More common in dogs.
Generalized splenomegaly: A
diffuse enlargement of the entire
spleen. More common in cats.