Persistent Müllerian Duct Syndrome Associated with a Sertoli Cell Tumor in a Male Schnauzer Dog

Persistent Müllerian duct syndrome (PMDS) is a rare disorder of sex development characterized by the persistence of Müllerian duct derivatives in genetically and phenotypically male animals. This report describes the clinical presentation, diagnostic work-up, surgical management, histopathological findings, and cytogenetic characterization of a 9-year-old intact male Schnauzer dog presented with a 3-day history of progressively worsening vomiting, diarrhea, unilateral testicular enlargement, oliguria, and dysuria. Diagnostic evaluation included abdominal radiography, ultrasonography, exploratory laparotomy, histopathology, and cytogenetic analysis using R-replicative banding after bromodeoxyuridine incorporation. Imaging and surgical exploration revealed cryptorchidism, persistent Müllerian duct derivatives, including uterine horn-like structures, and an abnormal gonadal structure. Histopathological examination confirmed severe seminiferous tubular atrophy, persistence of Müllerian-derived tissues, and a unilateral Sertoli cell tumor. Cytogenetic analysis demonstrated a normal male karyotype (78,XY) without evidence of chromosomal mosaicism or structural abnormalities, supporting the diagnosis of a 78,XY disorder of sex development and excluding major chromosomal defects. This case highlights the importance of integrating clinical evaluation, diagnostic imaging, histopathology, and cytogenetic analysis to identify findings compatible with PMDS and emphasizes that this condition should be considered in the differential diagnosis of cryptorchid male dogs presenting with reproductive tract abnormalities or associated testicular neoplasia.