A Case of Vanishing Testis in a Dog

SUMMARY Castration surgery was conducted on a 16-month-old Chihuahua diagnosed with bilateral cryptorchidism. Gross examination of the intra-abdominal and inguinal subcutaneous tissue revealed an atrophic testis in the subcutis of the right inguinal region, while only the spermatic cord, with its distal end being blind, was observed on the left side. Histopathologic examination revealed the presence of the epididymis, pampiniform plexus, and atrophic testicular parenchyma with a reduced number of seminiferous tubules that did not contain germ cells on the right side. In the left spermatic cord, only the vas deferens was histologically identified; testicular parenchyma or epididymis was undetectable. From these results, this case was diagnosed as vanishing testis, the term used for classification of monorchid testis in humans.