Biliary Cystadenoma in the Cat
Biliarycystadenomas are uncommon, benign hepatic tumors.
Most feline cases have been reported in cats greater than
ten years of age. Biliarycystadenomas may be unilocular or
multilocular and consist of thin-walled cysts that contain
clear, watery to slightly viscous fluid. The tumor is often
raised above the capsular surface and may involve more than
one liver lobe. The cysts vary in size from 1-15 mm and may
be arranged in masses as large as 12.5 cm. The tumor is usually
intrahepatic, but may rarely occur in extrahepatic ducts.
This neoplasm in man shows a predilection for females,
but no sex predilection has been found in cats. Although
at least one report claims it is more common in domestic shorthair
cats, there is no confirmed breed predilection. In humans,
biliarycystadenomas can undergo malignant transformation.
It is unclear, however, whether this occurs in the feline
species. Metastasis is not a reported feature of this neoplasm.
Abdominal pain is the most common sign in humans with this
tumor, but does not appear to be common in cats. The most
common signs in cats are anorexia, lethargy and weakness.
Patients may present with a cranial abdominal mass on palpation.
The tumor can also be demonstrated by radiography, ultrasonography,
computed tomography, or may be an incidental finding on necropsy
or exploratory laparotomy. In any case, signs associated
with the tumor seem to be related to impingement on other
organs rather than to the tumor itself. Blood abnormalities
are often present due to the age of the patient and the aforementioned
adjacent organ impingement, but there is no evidence of serum
biochemical or hematologic abnormalities directly associated
Radiographically, this lesion may be seen as a cranial
abdominal mass. Association
with the liver is often difficult to demonstrate. Ultrasound
is the diagnostic tool of choice since the cystic nature and
association with the liver are more apparent with this modality.
The cyst walls are thin and smooth. The contents of these
cysts are anechoic, but may occasionally contain internal
echoes. The ultrasonographic features alone are not enough
to definitively diagnose this tumor. Other differentials
include hematoma, abscess, parasitic cyst, biliary cyst or
tortuous biliary structures, cystadenocarcinoma, hemangiosarcoma,
feline polycystic disease of the liver and kidney, or metastatic
pancreatic and ovarian adenocarcinoma.
Final diagnosis is by histopathology. The lining of the
cyst is cuboidal to attenuated epithelium with occasional
papilla formation. The epithelium is histologically, immunologically
and electron microscopically similar to typical biliary epithelium.
The fibrovascularstroma surrounding the epithelium may contain
frequent islands of entrapped hepatocytes and occasional muscle
fibers and inflammatory cells. The cysts contain proteinaceous
fluid and varying amounts of mucin. The cyst contents help
to differentiate biliarycystadenoma from a biliary cyst, abscess,
or hematoma. Those would contain bile, pus or blood, respectively.
Aspiration and fluid cytology of the cyst contents are not
adequate for final diagnosis.
The origins of this tumor are obscure, but there is some
evidence that this slow-growing tumor may sometimes be congenital.
There is excessive production of the embryonic bile ducts
that may not be continuous with the biliary tree. These areas
would normally involute but may be retained as cysts or hamartomas
and may be the source of this tumor. It has also been shown
that these tumors can be acquired, as they have been experimentally
induced in rats.
The treatment of choice for biliarycystadenoma is complete
surgical excision with 1 cm margins. This may require complete
lobectomy in the cat. Cholecystectomy may also be required.
If complete removal is not possible, partial excision may
be adequate for good prognosis due to the slow-growing nature
of this tumor. Recurrence appears to be extremely rare, but
has been reported in at least one case. Other treatments,
such as aspiration, marsupialization, and partial excision
have met with limited success and are not recommended since
there may be a possibility of malignant transformation.
-by Mark Funk, Ross
-edited by Theresa Boulineau, ADDL Graduate student
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