A. DEVELOPMENT

Embryologically the testes form caudal to the kidneys. A gelatinous tissue, the gubernaculum, pulls the testes through the abdomen, through the inguinal canal in the groin, and down into the scrotum. The pulling action occurs as the gubernaculum is stimulated first to grow and then to shrink. Factors that promote growth and shrinkage of the gubernaculum are poorly defined. Testosterone is necessary, as is physical presence of the testis. Genetic factors play a role. Physical changes in the abdomen of the developing pup also are involved. In all male puppies, testes should be descended into the scrotum and readily palpable by 8 weeks of age.

Because the inguinal canal does not close until dogs are about 6 months of age, movement of testes from the scrotum back up into the inguinal region and abdomen may occur until that time. The timing of the closure of the inguinal ring varies with size of the dog. The inguinal ring may close earlier than 6 months in toy breeds and may close later than 6 months in giant breeds. Because average time of closure is 6 months, dogs are considered to have abnormal testicular descent if both testes are not easily palpable in the scrotum at 6 months of age.

Monorchidism (birth of a dog with only one testis) and anorchidism (birth of a dog with no testes) are extremely rare in dogs. Any male dog without two palpable scrotal testes at 6 months of age is considered cryptorchid. There is no diagnostic test that allows veterinarians to differentiate dogs with a hereditary cause of cryptorchidism from dogs with a nonhereditary, developmental cause of cryptorchidism, but the latter is considered rare compared with the former.

B. SIGNALMENT

Cryptorchidism is a hereditary defect. As a general rule, purebred dogs are at greater risk than are mixed-breed dogs, and the smaller variant within a breed is at greater risk than is the larger variant (for example, miniature poodles are at higher risk than are standard poodles). For a listing of breeds predisposed to cryptorchidism, see Appendix I. Mode of inheritance is not known. This is a sex-limited trait that is carried on one or more autosomes, which means that even though only males can exhibit the trait, it can be carried and passed on by either males or females.

C. HISTORY AND CLINICAL SIGNS

Affected dogs may or may not have come from a line of dogs known to have exhibited cryptorchidism in the past. Because the defect can be carried by females, they may throw the defect when bred to one male but not when bred to another.

When young, dogs exhibit no clinical signs associated with cryptorchidism. Other hereditary defects often occur in cryptorchid animals, however; these include luxating patella (dislocating kneecap), hip dysplasia, defects of the penis and prepuce, and umbilical hernias. Retained testes cannot make spermatozoa but do continue to make testosterone, so cryptorchid dogs will show normal breeding behavior and development of secondary sex characteristics. They also are equally as prone to testosterone-dependent diseases, such as benign prostatic hypertrophy and perianal adenomas, as are intact dogs with descended testes. Retained testes are more likely to become neoplastic in older male dogs than are descended testes, so older males may present with clinical signs consistent with testicular neoplasia (see below).

D. DIAGNOSIS

Diagnosis is by physical examination and careful palpation of the scrotum. Testes may be retained in the groin, in the inguinal canal, or in the abdomen. One or both testes may be retained. It is very difficult to palpate for retained testes, and those that are retained usually are smaller than descended testes, such that radiographs and ultrasound cannot be used routinely to identify the location of retained testes.

E. TREATMENT

All cryptorchid dogs should be castrated and both testes removed. This prevents transmission of this hereditary defect and nullifies the enhanced risk of testicular neoplasia in retained testes.

Medical therapy to promote testicular descent has been described. Gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin (hCG) is administered to cause testosterone release. There are anecdotal reports of success, but this procedure is not ethical, and I do not recommend its use. Similarly, surgically retrieving testes and tacking them into the scrotum is an invasive, unethical practice that cannot be recommended. Movement of these retained testes into the scrotum does not decrease their predisposition to neoplasia and does make a dog with a defect into a dog that could be shown in American Kennel Club (AKC)–approved conformation shows. This is in the best interest of neither the dog nor the breeder.

F. PROGNOSIS

Even though dogs with only one testis retained usually are fertile, cryptorchid male dogs should not be bred. A breeding that produced cryptorchid pups should not be repeated. Prognosis for life for cryptorchid dogs that are castrated is very good.

A. DEVELOPMENT

Orchitis, which is inflammation of the testis, and epididymitis, which is inflammation of the epididymis, may occur separately but usually occur together. The testes are immunologically privileged tissue, which means they form and are walled-off before the immune system forms and therefore are not recognized as “self” by the cells of the immune system. Any trauma or inflammation of the testes that ruptures the tight outer capsule of the testes allows inflammatory cells of the immune system to destroy testicular tissue, which they consider a foreign substance. Inflammation of the testes and the subsequent increase in temperature in the scrotum quickly destroy spermatogenic cells and cause testicular atrophy that often is irreversible. The most common causes of orchitis and epididymitis in dogs are direct trauma, perhaps from a dog fight or vehicular accident, and infection. Bacteria commonly associated with orchitis and epididymitis include Escherichia coli, Staphylococcus spp., Streptococcus spp., Proteus spp., mycoplasmata, and other bacteria that are normal flora in the male reproductive tract. Bacteria may be introduced into testicular tissue by direct trauma, by movement from the urethra, from an infected prostate, or through the bloodstream. Brucella canis is associated with epididymitis and must be considered a rule-out whenever testicular or epididymal swelling is present (see Chapter 20). Orchitis and epididymitis may be present in one or both testes.

B. SIGNALMENT

Orchitis is reported to occur more commonly in young dogs but may occur in intact male dogs of all ages. There is no breed predisposition reported for this disorder.

C. HISTORY AND CLINICAL SIGNS

In the acute phase of infection, the testes and epididymes are swollen. The scrotum is enlarged and is painful to the animal on palpation. It may be difficult to determine the scrotal contents because of the degree of swelling present. After the initial inflammatory reaction subsides, the testes atrophy, becoming small, firm, and nonpainful to the animal on palpation. Even if only one testis is infected, the swelling of that testis within the scrotum causes an increase in intrascrotal temperature and subsequent atrophy of the other testis.

D. DIAGNOSIS

Orchitis and epididymitis are usually diagnosed on physical examination. Fever may be present, and bloodwork may show evidence of infection. Fine-needle aspirate of the swollen testis yields fluid and cells that can be submitted for culture and cytology. Any growth of organisms is significant because testicular tissue should be sterile. Cytology is inflammatory. A serologic test or culture for canine brucellosis should be performed. Ultrasound of the testis reveals patchy testicular tissue. Ultrasound alone cannot definitively differentiate orchitis from other testicular abnormalities, including torsion of the spermatic cord and testicular neoplasia.

E. TREATMENT

Removal of both testes is strongly recommended. If B. canis is present, appropriate management of the animal is dependent on how it is housed (see Chapter 20). Antibiotics do not penetrate testicular tissue well and any benefit of prolonged therapy with antibiotics cannot be associated with a good outcome in most cases because prolonged exposure of the testes to high intrascrotal temperature and inflammation will lead to testicular atrophy even if infection is eventually controlled. In valuable breeding dogs with only one affected testis, removal of the affected testis and antibiotic therapy may allow retention of fertility. If the unaffected testis underwent collateral damage from the high intrascrotal temperature during the acute phase of orchitis, it may undergo compensatory hypertrophy and allow the animal to maintain fairly normal semen quality.