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Bovine Granulosa Cell Tumors

Granulosa cell tumors are the most common neoplasm involving the ovaries of cattle.  Even though they are the most common ovarian neoplasm, the incidence has been reported to be approximately 0.5 per cent.  Granulosa cell tumors affect all breeds of cattle but appear to occur more often in dairy cattle rather than beef cattle.  Of the dairy breeds, Guernseys and Holsteins are most frequently affected; however, these breeds also represent the majority of the dairy breeds in absolute numbers.

  The higher incidence of these neoplasms occurring in dairy cows may also be partially due to more intense reproductive management practiced on most dairy operations compared to beef cattle operations.  The reproductive status of a cow on a dairy farm is evaluated more frequently through repeated rectal examinations than beef cattle on average.  It has been proposed that this intense management results in a higher percentage of these tumors being diagnosed rather than dairy cattle being predisposed to developing them.  These tumors have been diagnosed in every age of cow, ranging from virgin heifers to very old cows.  Granulosa cell tumors have also been reported in pregnant cows, but the occurrence is rare.

  These tumors vary in size and structure and are rarely malignant.  They have been reported to range from 11.9 grams – 12.3 kilograms.  Granulosa cell tumors are most often unilateral and may suppress the function of the contralateral ovary.  When this occurs, the contralateral ovary becomes atretic while the ovary with the tumor may continue to grow.  These tumors vary in size from relatively small, solid, yellow to white structures to large structures composed of multiple cysts (some being as large as 7.5 cm in diameter), a single large cystic structure, or a combination of solid and cystic structures.  The surface of these tumors may be smooth or lobulated.  They may be so highly vascularized that one can palpate fremitus in the middle uterine artery.  The occurrence of malignant granulosa cell tumors is rare and metastasis is even more rare.  It has been reported, however, that an aged cow experienced metastases to the liver.

  Cows with granulosa cell tumors may present with a variety of clinical signs ranging from anestrus to nymphomania to male-like behavior.  Other clinical signs that may be present include abnormal estrous cycles, deepening of the voice, virilism, and mammary gland development.  Mammary gland development and colostrum-like secretions have been reported in virgin heifers.  The presence of vaginal discharge and enlargement of the vulva and clitoris may also be present.  Cows have also been presented for chronic weight loss due to persistent heat or male-like behavior.  These cows may be noticed constantly riding other cows within the herd expressing bull-like behavior.  The presence of each of the above clinical signs depends on how much functional luteal tissue is present within the tumor.  The amount of functional tissue relates to the dominant hormone being produced within the tumor.  In the majority of cases, the tumor continues to grow and may cause affected cows to progress through a series of various stages beginning with nymphomania and ending with virilism.

  Diagnosis of granulosa cell tumors is most frequently made through rectal palpation.  Most often one will palpate one ovary that is abnormally enlarged while the contralateral ovary will be small.  As a rule, granulosa cell tumors should be suspected when the affected ovary is greater than 10 cm in diameter.  In some cases, due to the size and/or weight of these tumors, it may be impossible to palpate  if located deep in the abdominal cavity.  Using a board to pry the abdomen from ventral to dorsal may be one way to make rectal palpation possible.  The use of cervical forceps may also be an option to retract the uterus and ovaries to make rectal palpation effective.  Ultrasound examination is another means of diagnosing granulosa cell tumors.  Upon ultrasound examination the affected ovary may appear to have a honeycomb appearance.  If the majority of the tumor tissue is solid the tumor will appear solid and may be misdiagnosed as a large corpus luteum.  A granulosa cell tumor should also be suspected when a chronic cystic structure does not respond to conventional treatment regimens.  Cystic ovaries may produce the same clinical signs as a granulosa cell tumor.  Monitoring a cow’s response to exogenous hormones or prostaglandins may aid in differentiating between the two conditions.  Another more practical way to differentiate between a granulosa cell tumor and cystic ovaries is serial rectal palpations.  Most often a granulosa cell tumor will continue to enlarge, whereas cystic ovaries tend to be more static.  However, the only way to have a definitive diagnosis for a granulosa cell tumor is through histopathological examination of the tumor sections.

  Treatment of granulosa cell tumors is limited.  Unilateral ovariectomy is the only treatment option available.  Most often, this is only used in valuable breeding stock.  It is not recommended to perform this on animals that exhibit changes in secondary sexual characteristics such as enlargement of the vulva and clitoris.  Animals showing these changes have a reduced fertility post surgical removal of the tumor.  It has also been reported that removing the ovary in cows exhibiting these changes resulted in cystic follicles on the contralateral ovary.  As a rule, cattle have reduced fertility after a unilateral ovariectomy when compared to the mare.  Economically it is often not feasible to perform surgery to remove the tumor on animals with average genetics.  The surgical approach for removing the ovary depends on the size and location of the ovary and the demeanor of the cow.  Most dairy cows will stand for the procedure, whereas beef cattle often need to be cast into lateral or dorsal recumbency.  If the ovary fits in the palm of one’s hand, most often the ovariectomy via colpotomy approach is successful.  In order to safely remove large tumors the surgical approach recommended is through a laparotomy incision in the paralumbarfossa or on ventral midline. 

Whichever technique is used, special care should be taken to avoid damaging the vasculature of the tumor to prevent hemorrhage.

 - by Brandon Brackenbury, Class of 2002

 -edited by Marlon Rebelatto, ADDL    Graduate Student

References

Amstutz, H.E.: 1980. Bovine Medicine and Surgery.American Veterinary Publications.Santa BarbaraCA

Carlton, William W., McGavin, M.D.: (1995). Thomson’s Special Veterinary Pathology, 2^nd edition.

Jones, Thomas C., Hunt, Ronald D., King, Norval W.: 1996. Veterinary Pathology.

Radostits, Otto M., Gay, Clive C., Blood, Douglas C., Hinchcliff, Kenneth W. : 2001.  Veterinary Medicine, 9^th edition.

Smith, Bradford P.: 2001.  Large Animal Medicine, 3^rd edition.

Youngquist, Robert E.: 1997.  Current Therapy in Large Animal Theriogenology

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