Todayโs path rounds are on ๐ ๐ซ๐๐ง๐ฎ๐ฅ๐จ๐ฌ๐ ๐๐๐ฅ๐ฅ ๐ญ๐ฎ๐ฆ๐จ๐ฎ๐ซ๐ฌ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐ซ๐๐ง๐ฎ๐ฅ๐จ๐ฌ๐ ๐๐๐ฅ๐ฅ ๐ญ๐ฎ๐ฆ๐จ๐ฎ๐ซ๐ฌ are tumours of granulosa cells, which are the cells of the ovary that produce hormones, primarily estrogen and progesterone. These tumours are often huge by the time they are detected, frequently replacing the whole ovary!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Any species can get this, but we most commonly see it in mares.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Because the tumour is derived from cells that produce hormones, the tumour cells are often also able to produce hormones. This leads to three possible outcomes for the mare: ๐๐ง๐๐ฌ๐ญ๐ซ๐ฎ๐ฌ, ๐๐จ๐ง๐ญ๐ข๐ง๐ฎ๐จ๐ฎ๐ฌ ๐๐ฌ๐ญ๐ซ๐ฎ๐ฌ and ๐ฆ๐๐ฅ๐ ๐๐๐ก๐๐ฏ๐ข๐จ๐ฎ๐ซ.
Anestrus means that the mare is not cycling at all. One of the hormones that granulosa cells can produce is ๐ข๐ง๐ก๐ข๐๐ข๐ง, which prevents release of ๐๐จ๐ฅ๐ฅ๐ข๐๐ฅ๐-๐ฌ๐ญ๐ข๐ฆ๐ฎ๐ฅ๐๐ญ๐ข๐ง๐ ๐ก๐จ๐ซ๐ฆ๐จ๐ง๐. Follicle-stimulating hormone is the main hormone from the pituitary gland, and its main job is to stimulate cycling within the ovary. Therefore, if the tumour produces high levels of inhibin, the mare will not cycle appropriately.
Conversely, if the tumour produces high levels of estrogen and progesterone, then the mare may cycle continuously. Being in โheatโ is often uncomfortable for mares, so this can frequently cause behavioural issues.
Finally, depending on the tumour, sometimes they can produce lots of testosterone. This is because testosterone is actually the precursor to estrogen, so the granulosa cells normally would make testosterone, then convert it to estrogen. If the tumour cells arenโt correctly converting the testosterone, then testosterone will accumulate, leading to stallion-like behaviours in these mares.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Often, these mares present with behavioural issues, or even not cycling and difficulty getting pregnant. Based on suspicion, the veterinarian may ultrasound them to look for an enlarged, cystic (looks like Swiss cheese) ovary characteristic of these tumours. The opposite ovary will also likely be small and non-functional.
At necropsy, granulosa cell tumours are quite characteristic, being large, cystic masses filled with fluid. Occasionally they can have solid areas that are occasionally yellow from testosterone accumulation.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
The only treatment available for these tumours is surgical removal. Usually, mares return to normal cycling within 6-8 months, and have normal fertility.
๐๐ก๐จ๐ญ๐จ๐ฌ
1-5) Various photos of granulosa cell tumours! Major Swiss cheese vibes 
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 3. Sixth Edition.
Photos 1-5 courtesy of Noahโs Arkive.
