Male pseudohermaphroditism in a Labrador Retriever, and a review of mammalian sexual differentiation.

CASE HISTORY: An 8-month-old Labrador Retriever was referred with a history of ambiguous external genitalia. CLINICAL FINDINGS AND TREATMENT: Clitoromegaly within apparent vulval folds, and an adjacent subcutaneous mass were noticed on external examination. An intra-abdominal testicle, with epididymis and suspected vas deferens ducts, was found during exploratory celiotomy. Incision over the subcutaneous mass revealed the accompanying testicle. Clitoridectomy was performed and an os clitoris removed. Normal juvenile testes were diagnosed on histology of the gonads. Chromosomal studies revealed a normal 78, XY male chromosomal constitution. Due to the combination of a male karyotype (78, XY), the presence of testicular tissue in the gonads, and the appearance of the external genitalia, a diagnosis of male pseudohermaphroditism (MPH) was made. CLINICAL RELEVANCE: This case presents the first report of MPH in a Labrador Retriever, and highlights the diagnostic steps recommended when confronted with a dog with ambiguous external genitalia.