The testicles can be retained within the abdomen, or within the inguinal canal. They also can have passed through the inguinal canal and just not be lying within the scrotum. Testicles that have passed through the inguinal canal, but are carried high in the flank rather than within the scrotum, are not considered retained. This can often be accomplished with the use of sedation. Sedation helps the horse relax, and the testicle often can be more easily palpated if it has descended through the inguinal canal.
Veterinarians also can use ultrasound to look for a retained testicle.
An ultrasound examination performed per rectum can determine if a testicle is retained within the abdomen. Furthermore, the inguinal area can be examined via ultrasound to determine if there is a testicle within or just outside the inguinal canal. In this way, a veterinarian can determine prior to anesthetizing a horse if a testicle is retained within the abdomen. Cryptorchid testicles cannot be removed in the same fashion as normally descended testicles, so to avoid unnecessary anesthesia and expense, it is better to know before surgery. Unfortunately, sometimes the descended testicle is removed and the cryptorchid testicle is left.