Cryptorchid Testicle in Dogs and Cats: Vet Guide

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

A cryptorchid testicle is a testis that never completed its descent into the scrotum. In dogs this is one of the most common developmental disorders of the male reproductive tract, and in cats it is uncommon but well documented. The retained gonad sits somewhere along its normal path, most often in the inguinal canal or the abdomen in dogs, and most often inside the abdomen in cats. The single most important fact for an owner is this: a retained testis carries a markedly increased risk of developing a Sertoli cell tumor or a seminoma, and the standard recommendation is surgical removal of both the retained testis and the descended testis.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Owner Triage Summary

If you have a young male puppy or kitten and you can only feel one testicle, or none, this is not an emergency on its own. It is a reason to book a veterinary visit.

Seek care the same day if a male dog or cat shows any of these:

• Acute abdominal pain, a hunched posture, or a firm abdominal mass
• Vomiting, inappetence, or marked lethargy in a known cryptorchid animal
• A swollen, painful, or hardened scrotum
• Sudden enlargement of the mammary glands or nipples in a male dog

Those signs can indicate torsion of a retained testis or a hormone-producing testicular tumor, and both require prompt veterinary assessment [1].

What Cryptorchidism Means

Cryptorchidism is the failure of one or both testes to descend into the scrotum [2]. The word describes a location problem, not a disease of the testis itself. The testis formed normally in most cases. It simply stopped moving.

Testicular descent in the dog is normally complete by six to eight weeks of age, though some authors extend the normal window to sixteen weeks [3]. Failure of descent beyond that window is considered pathological [3]. In practice, this is why veterinarians recheck the scrotum at every puppy visit through the first several months of life.

Two terms matter for owners:

• Unilateral cryptorchidism means one testis is retained and the other is in the scrotum. This is far more common than the bilateral form [4].
• Bilateral cryptorchidism means both testes are retained. These dogs are usually infertile [5].

A cryptorchid dog is still a male dog. He still has testosterone-driven behavior in most unilateral cases, because the descended testis continues to produce hormone. Owners are often surprised that a dog with one retained testis still mounts, marks, and shows interest in females in heat.

How Common Is It, and Who Is at Risk

Reported prevalence in dogs ranges from about 1% to 10% of the canine population [3]. A large ultrasound-based survey of 4,924 male dogs found cryptorchidism in 403 animals, or 8.2% [4]. That same study found the right testicle was affected more often than the left, at 59.5%, and that unilateral occurrence was far more common than bilateral, at 70% of cases [4]. When both testes were retained, the symmetrical form was most common, at 86.8% [4].

In cats, cryptorchidism is rarely encountered, with a reported prevalence below 3.8% [6]. A survey of testicular disorders in dogs and cats found that dogs carried a higher risk of testicular disorder and cryptorchidism than cats [7].

Breed and body size patterns in dogs

Body size shapes where the retained testis ends up. Cryptorchidism was more common in the inguinal region of small-breed dogs and in the abdominal region of medium- and large-breed dogs [4].

Breed predispositions appear in the clinical literature. In one prevalence study, pinscher, shih tzu, and poodle breeds had higher risks for ectopia, the category that includes retained testes [7]. The Maltese breed showed a high detection rate of testicular tumors and may carry elevated cryptorchidism risk [8]. A separate report of persistent Müllerian duct syndrome, a rare form of male pseudohermaphroditism often accompanied by cryptorchidism, notes that the condition has been found mainly in the Miniature Schnauzer [9]. An early anatomic and genetic study of a Miniature Schnauzer colony provided strong evidence for the hereditary nature of cryptorchidism in that breed, with morphologic findings suggesting a multiple gene defect [10].

Heritability

Cryptorchidism is heritable [3]. Genetics is the most significant factor behind the condition, and the hereditary basis is well established [3]. Hormonal factors including INSL3 and testosterone, mechanical factors such as narrowing of the inguinal canal and abnormalities of the gubernaculum, and environmental influences such as exposure to external estrogens and maternal stress during pregnancy all contribute [3].

Because the trait is heritable, affected dogs should not be bred. This is a breed-level welfare issue, not just an individual medical one.

Anatomy and Physiology: Why Descent Matters

Testicular descent is a complex process that depends on genetic and hormonal signals guiding the fetal gonad from its original position near the kidney down into the scrotum [11]. The hormone INSL3, also called insulin-like peptide 3, and its receptor RXFP2 play crucial roles in the transabdominal migration of the testes [11].

When descent fails, the testis remains at core body temperature. The scrotum exists to keep the testis a few degrees cooler than the abdomen, and that temperature difference is required for normal sperm production. A retained testis is therefore exposed to heat it was never designed to tolerate.

The consequences show up in the tissue. In cryptorchid testes, the first histological alterations appear from the peripubertal stage, around 6 to 8 months of age, and persist into old age [12]. Spermatogenesis is arrested at the level of spermatogonia, and a Sertoli-cell-only pattern is commonly seen in abdominal testes [6]. In one case report of a young dog with right-sided cryptorchidism, the retained right testis lacked spermatogenesis but contained normal Sertoli cells [13].

Retained testes are also physically smaller. On computed tomography, undescended testes measured around 70% of the size of scrotal testes and showed increased density on both pre- and post-contrast scans, likely reflecting reduced or absent spermatogenesis or other parenchymal changes [14].

Species Differences: Dogs Versus Cats

The retention pattern differs between the two species, and this shapes how each case is worked up.

Dogs

In dogs, the retained testis is usually inguinal or abdominal [4]. Location tracks with body size. Small breeds trend toward inguinal retention, and medium and large breeds trend toward abdominal retention [4]. In an early anatomic study of a Miniature Schnauzer colony, ectopic testes were in the abdominal position in all but one case [10].

Cats

In cats, abdominal retention predominates [6]. A case report of a 1-year-old male domestic longhair cat with right unilateral cryptorchidism located the retained testis within the abdomen on ultrasound, and the testis was found to be torsed at surgery [6]. Feline cryptorchidism is uncommon enough that each case tends to be reported individually, which is why the feline literature is thinner than the canine literature.

The practical takeaway for owners: in a cat with a missing testicle, expect the veterinarian to look inside the abdomen rather than in the groin.

Why Retained Testes Are Dangerous

The core risk is neoplasia. Cryptorchidism is a recognized predisposition factor for the development of testicular neoplasia [4]. The association is strong and consistent across studies.

In a 12-year retrospective study of 96 testicular tumors from 80 dogs, 52 tumors (54.2%) developed from cryptorchid testes in 45 dogs, while 44 tumors (45.8%) developed from scrotal testes in 35 dogs [8]. Cryptorchidism was significantly associated with the development of mixed germ cell-stromal cell tumors, Sertoli cell tumors, and seminomas, but not with interstitial cell tumors [8]. The detection rate of testicular tumors in dogs younger than 10 years old was significantly associated with cryptorchidism [8].

This is the central point of the article. A retained testis is at markedly increased risk of Sertoli cell tumor and seminoma. Those two tumor types are the ones most tightly linked to retention.

Sertoli cell tumors and feminization

Sertoli cell tumors in cryptorchid dogs are a distinct clinical problem. In a case series of intra-abdominal testicular torsion in cryptorchid dogs, testicular neoplasia included seminoma in two of four cases and Sertoli cell tumor in two of four, and both Sertoli cell tumor cases were associated with hyperestrogenism [1]. One of those had metastasized to the ipsilateral medial iliac lymph node [1].

Hyperestrogenism from a Sertoli cell tumor produces visible signs in male dogs, including mammary gland enlargement, pendulous prepuce, and attraction of other male dogs. Owners sometimes notice these changes before they notice anything abdominal.

Torsion

Torsion is a second major risk. Intra-abdominal cryptorchidism and testicular neoplasia are both risk factors for intra-abdominal testicular torsion, which may cause complete or incomplete vascular occlusion leading to ischemia and necrosis and which necessitates urgent orchidectomy [1].

Torsion is rare in cats but does occur. The first description of testicular torsion in a non-neoplastic abdominal testis of a tom cat involved a 1-year-old domestic longhair with right unilateral cryptorchidism whose abdominal testis was severely discolored with a twisted spermatic cord [6]. Histopathology showed severe diffuse congestion with marked interstitial hemorrhage and edema affecting both the testis and epididymis [6].

Fertility

Bilateral cryptorchids are usually infertile [5]. The bilateral condition is known to lead to fertility problems and to a predisposition to testicular cancer [5]. Concentrations of both INSL3 and testosterone were lower in bilateral cryptorchid dogs than in normal and unilateral cryptorchid dogs [15], which reflects reduced functional Leydig cell output when both gonads are retained.

Unilateral cryptorchidism is a different story. The descended testis may still produce sperm, and the dog may remain fertile. Whether the scrotal testis in a unilateral cryptorchid dog carries its own neoplastic risk is genuinely controversial in the veterinary literature, and the therapeutic approach to the canine unilateral cryptorchid has been described as arbitrary as a result [5].

Clinical Signs Owners Notice

Many cryptorchid dogs and cats show no signs at all. The condition is often discovered incidentally during a wellness exam or at the time of a scheduled neuter.

Signs that do appear tend to fall into three groups:

• Absence of one or both testicles on palpation
• Behavioral signs of intact male status in a dog the owner believed was neutered, or continued mounting and marking
• Signs of a hormone-producing tumor, including mammary enlargement in a male dog

Signs of torsion are acute and include abdominal pain, a palpable abdominal mass, inappetence, and vomiting [1].

Veterinary Examination: The Palpation Sequence

Palpation is the first and most important diagnostic step. The technique matters, and it should be done in a set order.

Step 1: Conscious examination

1. Place the dog or cat in a standing position if tolerated, then gently roll into lateral recumbency.
2. Identify the scrotum and confirm how many testes are present. Note the size, symmetry, and consistency of any testis you can feel.
3. Trace the spermatic cord upward from the scrotum toward the inguinal ring. An inguinal retained testis often sits just cranial to the pubis and can be rolled between your fingers.
4. Palpate the inguinal region on both sides with flat fingers, not fingertips. A small inguinal testis is easy to miss with a poking motion.
5. Palpate the caudal abdomen gently. An abdominal testis is usually not palpable unless it is enlarged or neoplastic.
6. Repeat the exam after a few minutes of quiet restraint. A tense puppy can retract a scrotal testis high into the inguinal canal and mimic retention.

Step 2: Sedation or ultrasound if not found

If the conscious exam does not locate the testis, the next step is either heavy sedation with a repeat palpation or ultrasound. Ultrasound is a valuable diagnostic tool for cryptorchid testes and gives precise localization plus information about parenchymal changes, which supports a safe clinical plan [4].

Ultrasound is the practical first-line imaging choice for most cases. It is non-invasive, does not require general anesthesia, and can identify both inguinal and abdominal testes in experienced hands.

Step 3: Advanced imaging or hormonal testing

Computed tomography identified retained testes and provided enhanced three-dimensional visualization compared to traditional ultrasound in a multi-center study of 19 dogs [14]. CT has clear advantages in spatial resolution and deeper tissue penetration, but it requires general anesthesia and involves radiation exposure [14]. CT is most useful when ultrasound is inconclusive or when a larger abdominal mass needs to be characterized.

Hormonal stimulation testing can help localize a retained testis when imaging is inconclusive. Human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone (GnRH) stimulation testing are used to demonstrate the presence of functional testicular tissue in an animal with no palpable testis. The logic is straightforward: if a cryptorchid testis is present and functional, stimulating it will raise testosterone above baseline, whereas a truly castrated animal will not respond.

Hormone measurement itself can also support the diagnosis. Anti-Müllerian hormone concentrations in peripheral blood were elevated in a cryptorchid group in one study [16], and plasma INSL3 concentrations were lower in bilateral cryptorchid dogs than in normal and unilateral cryptorchid dogs [15]. These are adjunct tests, not replacements for palpation and imaging.

Diagnostic Workup: What Your Vet Is Looking For

The workup answers four questions:

1. Is one testis missing, or both?
2. Where is the retained testis?
3. Is the retained testis neoplastic or torsed?
4. Is the descended testis normal?

A complete blood count and chemistry panel are reasonable baseline tests, particularly in an older cryptorchid dog. One case report of a young dog with right-sided cryptorchidism and contralateral testicular torsion found mild anemia and elevated urea levels on bloodwork [13]. Those findings are not specific to cryptorchidism, but they illustrate why baseline labs are part of a full workup in a symptomatic animal.

If a Sertoli cell tumor is suspected because of feminization signs, serum estradiol can be measured. Elevated serum estradiol was documented in dogs with cryptorchid testicular tumors [9].

Decision Table: Neuter Timing by Species, Location, and Age

Two practical notes on this table. First, the age at diagnosis is not the same as the age at which risk becomes high. Neoplastic transformation takes years in most cases, which is exactly why early removal is preferred over waiting. Second, in a cat, the retained testis is usually found at the time of a routine neuter, and the surgeon should be prepared to convert a scrotal procedure into an abdominal exploration.

The Surgical Decision: Why Both Testes Are Removed

Standard cryptorchid neuter involves removal of the retained testis and the descended testis. This is not a matter of convenience. It is a matter of risk management.

The reasoning is:

• The retained testis is at markedly increased risk of Sertoli cell tumor and seminoma [8].
• The retained testis is at risk of torsion [1][6].
• Leaving the descended testis behind preserves testosterone-driven behavior and does not remove the risk from the retained gonad.
• In bilateral cases, both testes are retained and both are at risk [5].

A cryptorchidectomy is a more involved procedure than a routine scrotal neuter. An abdominal testis requires an abdominal approach. An inguinal testis requires an inguinal approach. Owners should expect a slightly longer anesthesia time and a slightly longer recovery than a standard neuter, and they should ask their veterinarian about the specific plan before the day of surgery.

In one documented case, a left orchiectomy and right cryptorchidectomy were performed together, and the dog experienced no post-operative complications and was in good health at a 2.5-month follow-up [13]. That is the typical outcome when the procedure is done before a tumor or torsion develops.

The Main Decision Path

The flowchart below traces the path from a missing testicle to the surgical decision.

flowchart TD
    A[One or both testicles missing] --> B[Conscious palpation exam]
    B --> C{Testis located}
    C -->|Yes| D[Confirm location and plan surgery]
    C -->|No| E[Sedation or ultrasound]
    E --> F{Testis located}
    F -->|Yes| D
    F -->|No| G[hCG or GnRH stimulation test]
    G --> H{Functional tissue present}
    H -->|Yes| I[Presume retained testis]
    H -->|No| J[Reassess for prior castration]
    I --> D
    D --> K[Remove retained and descended testes]

What Happens If You Do Nothing

Some owners ask whether a cryptorchid dog can simply be left intact. The honest answer is that this is a risk trade, and the risk is not small.

The retained testis does not improve with age. Histological alterations in cryptorchid testes appear from the peripubertal stage and persist through the senile stage [12]. The neoplastic association is strong enough that cryptorchidism alone or in combination with age significantly affects the incidence and type of canine testicular tumors [8].

There is also a genetic cost. Because cryptorchidism is heritable [3], an intact cryptorchid dog that sires a litter can pass the trait on. Responsible breeding practice excludes affected dogs.

Unsafe Home Remedies and Myths

There is no home remedy that makes a retained testis descend. Hormone injections, massage, and "waiting it out" past the normal descent window are not supported. Testicular descent is normally complete by six to eight weeks of age, with some authors extending the window to sixteen weeks, and failure of descent beyond that window is pathological [3].

Three specific myths are worth correcting:

• "He will grow into it." Descent is a developmental event with a defined window. A testis that has not descended by the end of that window is not going to drop on its own [3].
• "If I can feel one testicle, he is fine." Unilateral cryptorchidism is the more common form [4], and the retained testis still carries elevated neoplastic risk [8].
• "A cryptorchid dog cannot father puppies." Unilateral cryptorchid dogs may remain fertile because the descended testis can still produce sperm. Only the bilateral form is reliably associated with infertility [5].

Do not attempt to manipulate or massage a suspected retained testis at home. You can cause discomfort and you will not change the outcome.

Prognosis

Prognosis for a cryptorchid dog or cat that undergoes surgery before a tumor or torsion develops is excellent. Orchidectomy was curative in five of six dogs in a case series of intra-abdominal testicular torsion [1], and the dog in the case report with combined orchiectomy and cryptorchidectomy recovered without complications [13].

Prognosis is more guarded once a tumor has developed. Sertoli cell tumors can metastasize, and metastasis to the ipsilateral medial iliac lymph node has been documented [1]. Early surgery is the single most effective way to avoid this scenario.

Prevention

The only true prevention is genetic. Because cryptorchidism is heritable [3], affected dogs should not be bred, and their close relatives should be evaluated carefully before breeding decisions.

Owners can support prevention at the population level by:

• Neutering affected dogs so they cannot reproduce
• Reporting the diagnosis to the breeder
• Choosing breeders who screen breeding stock and exclude affected lines

There is no diet, supplement, or environmental change that prevents cryptorchidism.

Limitations and When to Contact a Veterinarian

This article covers general principles. Individual cases need a veterinarian who can examine the animal.

Contact a veterinarian promptly if:

• A puppy older than four months has fewer than two palpable testicles
• A kitten has fewer than two palpable testicles at the time of a scheduled neuter
• A known cryptorchid dog or cat develops vomiting, inappetence, lethargy, or abdominal pain
• A male dog develops mammary gland enlargement, a pendulous prepuce, or nipple swelling
• A male dog or cat develops a swollen, painful, or hardened scrotum
• A previously diagnosed cryptorchid animal has not had surgery and the owner wants to discuss timing

Contact a veterinarian the same day if there is acute abdominal pain, a palpable abdominal mass, or a rapidly enlarging scrotum. Those findings raise concern for torsion, which necessitates urgent orchidectomy [1].

Frequently Asked Questions

Can a cryptorchid dog still father puppies?

Yes, a unilaterally cryptorchid dog can still be fertile because the descended testis may produce sperm. Bilateral cryptorchids are usually infertile [5].

Is cryptorchidism in dogs inherited?

Yes. Cryptorchidism is heritable, and genetics is the most significant factor behind the condition [3].

Which testicle is more commonly retained?

The right testicle is affected more often than the left, at about 59.5% of cases in one large survey [4].

Is cryptorchidism more common in dogs or cats?

It is much more common in dogs. Reported canine prevalence ranges from about 1% to 10% [3], while feline prevalence is below 3.8% [6].

Where is the retained testicle usually located in a cat?

In the abdomen. Abdominal retention predominates in cats [6].

Does a retained testicle always become cancerous?

No, but the risk is markedly increased. Cryptorchidism is significantly associated with Sertoli cell tumors, seminomas, and mixed germ cell-stromal cell tumors in dogs [8].

Can a retained testicle be left in place if the dog is older?

Surgery is still recommended. Retained testes carry ongoing neoplastic and torsion risk regardless of age, and histological changes in cryptorchid testes persist into the senile stage [12].

How is a retained testicle found if palpation fails?

Ultrasound is the usual next step and can localize the testis and assess parenchymal changes [4]. CT provides enhanced three-dimensional visualization when needed [14], and hCG or GnRH stimulation testing can help confirm the presence of functional testicular tissue.

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Sources

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3. Laterality and Breed Distribution of Cryptorchidism in 251 Dogs: A Retrospective Clinical Study.
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5. Immunohistochemical insights into a hidden pathology: Canine cryptorchidism.
6. Testis torsion in a non-neoplastic cryptorchid testis of a cat.
7. Prevalence of testicular disorders in dogs and cats in Fortaleza from 2020 to 2023.
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10. An anatomic and genetic study of canine cryptorchidism.
11. Analysis of transcript and methylation levels of INSL3 and RXFP2 in undescended and descended dog testes suggested promising biomarkers associated with cryptorchidism.
12. Cryptorchidism: The dog as a study model.
13. Right-sided cryptorchidism and contralateral intrascrotal testicular torsion in a young dog: a rare case report.
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