Clinical and Histological Findings of Male Uterus (Uterus Masculinus) in Three Dogs (2014–2018)

SIMPLE SUMMARY: In this study, we report the clinical and histopathologic diagnostic workup of three cases of uterus masculinus, the Müllerian duct remnant, in dogs. In the literature, single case reports describe this pathology in the canine species and, among other domestic mammals, in the horse. Its definitive diagnosis requires a specialized approach by integrating diagnostic imaging, surgery and histopathology analysis; furthermore, inflammation of uterus masculinus in the dog should be listed as a differential cause of abdominal pain. ABSTRACT: Data from three cases of uterus masculinus were retrieved from 2014 to 2018. Two out of three cases presented clinical signs compatible with systemic infection, as observed in bitches with pyometra. Ultrasound examination revealed a tubular fluid-filled structure with a thin irregular wall located cranially to the prostate and in continuity with the cranial part of the gland. In two cases, two other tubular fluid-filled structures were visualized in the caudal part of the abdominal cavity, ventrally to the prostate gland and urinary bladder. After surgical removal of these, histological examination revealed the presence of a uterine structure morphologically similar to the female counterpart. Various types of epithelial cell lining were found, including simple columnar, simple stratified and squamous epithelium associated with glands in the underlying stroma. Immunohistochemistry to anti-Müllerian hormone (AMH) produced a positive result on glands, while multifocal expression was found in the lining epithelium. AMH seems involved in the pathogenesis of uterus masculinus, but its role is not fully understood. Thorough clinical and ultrasonographical examinations, followed by a histological confirmation, are necessary to properly diagnose uterus masculinus in dogs.