Intra-abdominal testicular torsion in a horse without signs of colic.

A 5-year-old Quarter Horse stallion was admitted for cryptorchidectomy. Abnormalities were not found on physical examination, except for an undescended left testis. Cryptorchidectomy was performed, using an inguinal approach. The tail of the epididymis was in the inguinal canal, and the testis was adjacent to the internal inguinal ring. The testis was dark reddish purple to black, resulting from torsion at the level of the body of the epididymis. On histologic examination, the left testis was necrotic, except for the tunica albuginea and tunica vaginalis visceralis covering the testis. Intra-abdominal testicular torsion developed without signs of abdominal pain and resulted in necrosis of the affected testis. If cryptorchidectomy had not been performed, it is likely that the horse would have been found to be monorchid. Unrecognized intra-abdominal testicular torsion may be the cause of monorchidism in some horses.