Normally, a male puppy's testicles descend from his abdomen into his scrotum by the time he's 2 weeks old. Sometimes, one or both of his testicles don't drop, remaining somewhere in between his abdomen and the scrotal sac. That retained testicle must be surgically removed, because leaving it inside the dog's body can have unfortunate long-term consequences.
Dogs with only one descended testicle are unilaterally cryptorchid, while if both don't drop they are bilaterally cryptorchid. A vet can't just remove the dropped testicle and consider the dog neutered, nor can you figure your dog is essentially neutered if both testicles are absent. The vet finds the retained testicle beforehand either by palpation, if it's close to the scrotum or locating it via ultrasound. Since abdominal surgery is necessary to retrieve the testicle, the recovery period for your male dog is a couple of weeks.
Dogs with retained testicles face a far greater risk of testicular cancer than intact males with both testicles descended. If the retained testicle isn't removed by the dog's third birthday, he runs a 50 percent risk of it becoming malignant, with the cancer metastasizing throughout his body. Intact male dogs also run the risk of testicular cancer, but owners usually notice the enlargement and changes in the testicles and seek veterinary assistance. Usually, neutering solves the problem if the cancer hasn't spread. If the testicular tumor grows inside the dog, fatal issues can arise even before metastasizing. The tumor could burst, causing a septic reaction.
One early sign of cancer in a dog's retained testicle is feminizing. The tumor can secrete estrogen, causing changes in your dog's appearance and behavior. You might notice your dog's teats swelling, or he could start peeing like a girl. Intact male dogs might appear sexually interested in him. Other physical changes include hair loss and skin darkening.
While testicular torsion rarely occurs in intact male dogs, it's common in those with a retained testicle. The undescended testicle attaches to a ligament that in turn attaches to the dog's body wall. Testicular torsion occurs when the testicle become entangled in the ligament. The twisting cuts off the blood supply to the testicle, causing intense pain. Torsion and testicular cancer can be related, as the tumor in the testicle causes enlargement and subsequent tangling in the ligament. Surgical removal is the only treatment for testicular torsion.