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Cryptorchidism is a condition in which one or both testicles of your pet fail to descend into its scrotum. It is a very common problem in dogs and cats and is probably the most common birth defect that veterinarians encounter. It is seen more commonly in purebred than random-bred (crossbred,moggy) pets.
I see about three dogs with this problem for every cat. This is probably because so many ordinary family cats in the United States have a rich genetic pool.
We know this problem is genetic because it runs in families or lines. Miniature schnauzers, cocker spaniels, Chihuahuas and Persian cats have more than their fair share of cryptorchidism but any breed can be affected.
Dog and cats in which both testicles fail to make their journey to the scrotum are usually sterile. When testicles remain in the pet's abdomen the 4-5 degree higher temperature there usually prevents the production of viable (functional) sperm. It does not, however, affect the production of testosterone, so these pets exhibit typical male behavior. When one testicle does descend into the scrotum the pet will be fertile. When two missing testicle are under the skin near the scrotum, the pet may be fertile. But it is a very bad idea to breed dogs and cats that are cryptorchid because their descendants will carry the same defective genes.
Cryptorchid dogs and cats have a higher rate of developing a certain cancer call a Sertoli cell tumor. The Sertoli cells, which are located in the testicles, provide nourishment to the sperm cells. They also produce feminizing hormones (estrogens). These tumors often cause thin skin, sparse hair coat, aplastic anemia, enlarged breasts and sexual attractiveness to other male dogs. The hair loss in these cases is very specific in that it is identical on both sides of the pet's body (bilaterally symmetrical). You veterinarian may need to do ultrasound examination of the retained testicle as well as a plasma estrogen level to confirm the diagnosis.
Ten to twenty percent of these tumors are malignant and can metastasize (move) to other parts of the body. If the tumor has spread it can usually be treated successfully with chemotherapy. To avoid this debilitating treatment, your veterinarian will probably suggest that the cryptorchid testicle be located and removed before it has an opportunity to become cancerous. I let the pet's body fully mature before depriving it of the important androgens that testicles produce. Another problem that occurs in rare instances in cryptorchid pets is torsion (twisting) of the spermatic cord , the sperm duct that is attached to each testicle.
Cryptorchidism in dogs over twelve weeks of age is easy to see if the scrotal area of your pet is examined. It is a bit harder to detect in cats this young. An experienced person needs only pass the scrotum through pinched fingers to notice that only one or none of the testicles are present. The younger the pet, the smaller the testicles will be; so examination of small puppies and kittens has to be thorough and performed by an experienced individual.
In more than half of the cases, veterinarians can palpate (locate with their fingers) the missing testicle just forward of the scrotum or in the fat located in the animals groin. In these case, testicles have been relocated into the scrotum. Sometimes, testosterone therapy allows the retained testicle to descend into the scrotum when it is not quite there.
I do not feel that either of those procedures should ever be done. Doing so, or breeding your cryptorchid pet, perpetuates the disease in future generations of dogs and cats. Instead, have your pet neutered so that both testicles are removed and it can not pass this defective trait on to future generations. If you did not intend to neuter your pet, have the undescended testicle removed to preserve your pet's future health. Living with a sexually intact male cat is a challenge. But not every male dog needs to be neutered and none of them need to be neutered before they are sexually mature. You can read my thought on that here.
A special problem comes up when an adult dog or cat of either sex appears to be castrated or spayed but still exhibits male or female sexual behavior. In those instances, veterinarians can be uncertain if they are dealing with a castrated male cat or dog with other health issues, a cryptorchid pet whose undescended testicle was not located and removed, or a pet with a hormone imbalance of some other kind. In those cases, more tests will need to be run. Sometimes the retained testicle can be visualized in the abdomen through ultrasound. When this is not the case, the pet can be given an injection of chorionic gonadotropin. If this hormone causes a rise in serum testosterone level one hour after injection, we are most likely dealing with a cryptorchid pet. When this question occurs in a cat, we can examine the penis for spines. Spines are much smaller in castrated cats than in cats that still have their testicles – cryptorchid or not.
Testicles migrate from the abdomen to to the scrotum through two small holes in the groin called the inguinal rings. When the missing testicle or testicles have not passed through the inguinal rings and are still located in the abdomen, the surgery is much more complicated than when they have moved farther along on their journey to the scrotum.
In those cases, your veterinarian must, in effect, neuter and "spay" the same animal. The missing testicle can be anywhere between the rear (posterior) pole of the kidney and the inguinal ring and it can be nerve-racking to find and remove it - particularly if your pet is overweight. These testicles are much smaller and softer than the descended ones and are extremely difficult to locate in the fat that occupies the posterior abdominal (retroperitoneal) space. What usually allows me to find them is the epididymis or sperm collecting tubules that retain their distinctive appearance and "bumpy" feel through my gloves.
Dogs and cats that are cryptorchid have a slightly higher incidence of other genetic defects such as inguinal and umbilical hernias, abnormally formed penises and sheaths, as well as patellar luxations (trick knees).
Some authorities suggest waiting up to six months before deciding that the testicle(s) are not going to descend. I have never seen a case where the testicle(s) were not descended at twelve weeks of age but descended later. Late descent, during the first year of life, is common in humans - but humans stand erect and gravity probably helps move human testicles down.