Ovarian teratoma in a Swiss mountain dog.

A Swiss mountain dog, ~3 y old, was brought to a veterinary clinic because of a progressive enlargement of the abdomen. Upon clinical examination, a large mass was detected. After surgical extraction, the mass was confirmed to be a large ovarian teratoma. The weight of the tumor was > 16% of the dog's overall body weight. The dog recovered fully after surgery. The observations from this case suggest that, although teratomas are rare, prompt and accurate diagnosis is necessary to prevent further growth of these masses and to ensure positive outcomes.