Cryptorchidism (Retained Testicle)

Most cases of cryptorchidism are discovered during a routine physical examination when one (or both) scrotal positions are empty. Additional findings may include:

• One or both testicles absent from the scrotum — the scrotum may appear smaller or asymmetrical
• A palpable soft mass in the inguinal (groin) region or under the skin of the lower abdomen if the testicle is inguinally retained
• Normal male hormone behaviors (marking, roaming, mounting) even after a routine neuter — a sign that a testicle was missed or that an abdominal testicle was not removed at the time of the procedure
• In older intact cryptorchid males: signs of testicular torsion — sudden severe abdominal pain, vomiting, lethargy — which is a surgical emergency requiring immediate care
• Signs of a Sertoli cell tumor from the retained testicle (most common tumor in cryptorchid dogs): symmetrical hair loss, darkening of the skin, feminization (enlarged nipples, attraction of other males), or bone marrow suppression causing lethargy and pale gums

Cryptorchidism has a clear genetic basis and is one of the most heritable traits in dogs. It is far less common in cats but does occur:

• Genetics and heredity — the condition is transmitted through both sires and dams, even though only males are clinically affected. Breeding a cryptorchid male perpetuates the trait; for this reason, cryptorchid dogs are typically excluded from breeding programs
• Breeds commonly affected — Toy and Miniature Poodles, Chihuahuas, Pomernians, Yorkshire Terriers, Maltese, Boxers, Dachshunds, and Shetland Sheepdogs, among others. Purebred dogs are affected more often than mixed breeds overall
• Unilateral vs. bilateral — most cryptorchid dogs retain only one testicle (unilateral); bilateral retention (both testicles absent from the scrotum) is less common and results in infertility
• Cats — cryptorchidism in cats is less frequent; Persians and other pedigree breeds have slightly higher prevalence. An apparently neutered cat displaying intact-male behaviors should be evaluated for a retained testicle

Diagnosis begins with physical palpation — the scrotum and inguinal region are carefully examined to locate any retained tissue. When the testicle cannot be palpated externally:

• Abdominal ultrasound identifies an intra-abdominal testicle in most cases, along with any associated changes (enlargement, abnormal architecture suggesting early tumor)
• In ambiguous cases — for instance, determining whether an apparently neutered male was actually fully castrated — a hormonal challenge test (hCG or GnRH stimulation with testosterone measurement) can confirm the presence of functional testicular tissue
• Bloodwork is performed pre-operatively and, in older dogs with possible tumor-related feminization or bone marrow suppression, a complete blood count evaluates for estrogen-related anemia

Surgical removal (cryptorchid castration) is the recommended treatment for all cryptorchid males, regardless of whether one or both testicles are retained. Hormonal stimulation to encourage testicular descent is not recommended in veterinary medicine — it is not reliably effective and does not reduce cancer risk in a testicle with abnormal position.

• Inguinal cryptorchidism — a small incision over the inguinal region allows removal of the retained testicle; the opposite (normally descended) testicle is removed through a standard scrotal or prescrotal approach at the same time
• Abdominal cryptorchidism — requires an abdominal approach (laparotomy or minimally invasive laparoscopy in appropriately sized patients) to locate and remove the testicle from within the abdomen

Surgery is ideally performed before two years of age and before any signs of cancer develop. A cryptorchid testicle that has become a tumor (particularly Sertoli cell or seminoma) is still removed surgically, but additional staging and possible referral for oncology consultation are appropriate if malignancy is confirmed on histopathology.

If a puppy or young male dog has only one (or no) palpable testicles by six months of age, schedule an evaluation. The testicles are expected to be in the scrotum by six to eight weeks of age in dogs, and a testicle still absent at six months is unlikely to descend further on its own. Cats should be evaluated similarly. Early surgical correction prevents the long-term cancer risk and eliminates the possibility of testicular torsion — a painful emergency. If an apparently castrated male is still marking, roaming, or showing other intact behaviors, the team can evaluate for a missed retained testicle. Book an appointment at Dog & Cat Hospital Calabasas to discuss surgical removal.