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 with biliarycystadenoma.

  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 University Student

-edited by Theresa Boulineau, ADDL    Graduate student

References

Adler, R., Wilson, D.W.: 1995.  Biliarycystadenomas of cats.  Vet Path 32: 415-418.

Nyland, T.G., Koblik, P.D., Tellyer, S.E.: 1999.  Ultrasonographic evaluation of biliarycystadenomas in cats.  Vet Radiology and Ultrasound  40: 300-306.

O’Brien, R.T.: 1998.  Ultrasound corner attenuation: The clinical utility of subjective sonographic assessment.   Vet Radiology and Ultrasound  39: 224-225

Peterson, S.L.: 1984.  Intradepaticbiliarycystadenoma in a cat.  Feline Practice  14: 29-32.

Trout, N.J.: 1997.  Surgical treatment of hepatobiliarycystadenomas in cats.  Seminars in Vet Med and Surg  12: 51-53.

Trout, N.J., et al:  1995.  Surgical treatment of hepatobiliarycystadenomas in cats: five cases (1988-1993).  JAVMA  206: 505-507.