A 7-year-old female Yorkshire terrier dog presented with anorexia and fever due to pyometra; ovariohysterectomy was therefore performed. Histopathological examination showed multiple cysts of variable sizes with hyperplasticity of luteal cells, and the patient was diagnosed with cystic ovarian disease. An abnormal growth and infiltration of adipocytes in the uterus, especially at the border between the endometrium and myometrium, was accidentally identified. Based on the clinical features and histopathological findings, a diagnosis of pure uterine lipoma along with ovarian cystic disease was made. Further immunohistochemical study revealed that the lipomatous tissue was positive for the protein S-100, vimentin, and desmin, as well as estrogen receptors alpha and beta, which is in contrast to humans. Our results suggest a possible role of estrogen receptor signaling in abnormal lipomatous tissue changes in the canine female genital tract. We present here the first case of pure uterine lipoma in a dog and describe its characteristics.

Key words: Adipocyte, Canine, ER-α, ER-β, Pure uterine lipoma