Pseudo-placentational endometrial hyperplasia in a dog.

Ovariohysterectomy in a healthy, nonpregnant, non-pseudopregnant, 9.5-month-old female dog revealed a 3 cm in diameter, swollen segmental portion of the uterus. A large amount of mucoserous fluid was present in the segmental portion, and the mucous membrane was covered by many yellowish-white villi protruding into the lumen. Histopathologic examination revealed endometrial hyperplasia associated with dilatation of the uterine glands in the segmental portion. The morphological findings were quite similar to those of a maternal placenta of pregnancy without the fetus and fetal membrane. Accordingly, this young female dog was diagnosed with spontaneous pseudo-placentational endometrial hyperplasia.