LORI.equine

Malignant dysgerminoma in a mare 

Keywords: dysgerminoma, mare, equine, ovary, seminoma, neoplasia

  

Images by Dr Rob Lofstedt and Dr Shannon Martinson; case description by Dr Shannon Martinson, dept pathology, AVC.

An 8 year old Appaloosa X mares lost weight over 6-8 weeks and was inappetent for the last 2 weeks. She was presented with acute colic that could not be managed with analgesics. She was euthanized. 

As shown below, a firm lobulated tan mass measuring approximately 8 - 10 cm x 5 -6 cm was present in the neck at the thoracic inlet and continued as a chain of firm nodular masses in the cranial mediastinum.  These masses occupied a space of ~ 15 cm x 7 x 7 cm in total.  The masses were solid with central regions of necrosis.

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A large mass (shown below) obliterated the left ovary. It measured approximately 36 x 26 cm with a roughened/ruptured brown and red surfaces.  

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On cut section (as shown above) the mass was solid and tan colored with extensive regions of hemorrhage and necrosis. There were scattered areas of osseous metaplasia in the mass. It also contained several pockets of viscous tan to yellow exudate.  The right ovary (circled above) was active containing numerous follicles.  The uterus was unremarkable.  

The morphologic and histological diagnosis was that of a malignant dysgerminoma (details available on request).

Dysgerminomas are rare tumors of the ovaries in mares. They are of germ cell origin; the counterpart to seminomas in males.  In mares, these tumors appear to be more aggressive than in other species and metastasis is not uncommon. Metastases may occur to the regional lymph nodes or transcoelomically.  Interestingly, mares with disseminated dysgerminoma may develop hypertrophic osteopathy. This was not evident grossly in this case.