Maternal placenta-like endometrial hyperplasia in a beagle dog (Canine deciduoma).

Three thumb-sized segmental swellings were found in both uterine horns of a 15 month-old, non-pregnant and non-pseudopregnant female beagle dog. Histopathological examination of the uterus revealed a marked proliferation of the endometrium that was characterized by two distinct parts, an inner tightly-folded banded layer and an outer dilated spongy layer, quite similar to the maternal placenta except for the fetus and chorion in the lumen. Because the plasma level of progesterone was unusually high at autopsy, this hormonal disorder might be related to the pathogenesis of the endometrial hyperplasia in the present case.