Cryptorchidism

Cryptorchidism is a congenital developmental anomaly characterized by the failure of one or both testes to descend into the scrotum. In the dog and cat, the testes normally migrate from the abdominal cavity through the inguinal canal into the scrotum by 10 to 14 days of age, with complete descent typically achieved by 6 to 8 weeks. The condition is classified as unilateral (monorchidism is a misnomer; the retained testis is present but ectopic) or bilateral, and by location: abdominal (retained within the abdomen), inguinal (within the inguinal canal), or prescrotal (subcutaneous, just proximal to the scrotum). Surgical management, primarily bilateral orchiectomy, is the standard of care due to the high risk of testicular neoplasia and torsion, as well as the hereditary nature of the condition. The surgical approach varies depending on the location of the retained testis, with abdominal cryptorchidism requiring a celiotomy or minimally invasive laparoscopic-assisted techniques.

Cryptorchidism is a polygenic, sex-limited autosomal recessive trait with incomplete penetrance. The primary etiological factor is a failure of the normal hormonal and mechanical processes guiding testicular descent. During embryogenesis, the testes develop from the urogenital ridge and are anchored to the inguinal region by the gubernaculum. Testicular descent is mediated by androgens (testosterone), insulin-like peptide 3 (INSL3), and the genitofemoral nerve, which releases calcitonin gene-related peptide (CGRP) to guide gubernacular migration. A deficiency or insensitivity to these hormones, or an anatomical obstruction (e.g., a short gubernaculum, abnormal vaginal process, or fibrous adhesions), can arrest descent. In dogs, the right testis is more commonly retained than the left, and unilateral cryptorchidism is more frequent than bilateral. The condition is heritable, and affected animals should not be used for breeding. No single gene mutation has been identified, but genome-wide association studies have implicated loci on canine chromosomes 1, 10, and 19.

Cryptorchidism is one of the most common congenital defects in dogs, with an estimated incidence of 1% to 15% depending on breed and population. It is less common in cats, with an incidence of approximately 1% to 3%. Breeds with a high predisposition include the Boxer, German Shepherd Dog, Pomeranian, Yorkshire Terrier, Miniature Schnauzer, Siberian Husky, and various toy breeds. In cats, the Persian and Siamese breeds are overrepresented. The condition is more frequent in purebred animals, suggesting a genetic basis. Unilateral cryptorchidism is more common than bilateral, with the right testis affected more often. Bilateral cryptorchidism is associated with infertility, as the intra-abdominal temperature impairs spermatogenesis, although Sertoli cell tumors and Leydig cell tumors may produce hormones that maintain some libido. The condition is diagnosed in young animals, typically at the time of routine neutering, but may be identified later due to complications such as testicular torsion or neoplasia.

The pathophysiology of cryptorchidism involves the failure of testicular descent, leading to the retention of the testis in an ectopic location. The undescended testis is subjected to the higher core body temperature, which disrupts spermatogenesis and predisposes the testis to neoplastic transformation. The retained testis is often smaller and softer than the scrotal testis, and the epididymis may be abnormally elongated or detached. The gubernaculum, which normally shortens and pulls the testis into the scrotum, may be hypoplastic or fail to develop. In abdominal cryptorchidism, the testis may be located near the caudal pole of the kidney, within the inguinal ring, or anywhere along the path of descent. The testis is often mobile and may be found adjacent to the bladder or within the inguinal canal. The vascular supply (testicular artery and vein) and the ductus deferens are elongated, which can complicate surgical retrieval. The retained testis is at increased risk for Sertoli cell tumors, seminomas, and Leydig cell tumors, with a reported risk of 13.6 times that of scrotal testes. Testicular torsion is also more common, particularly in abdominal cryptorchid testes, due to the lack of scrotal attachment and the mobility of the mesorchium.

Intrinsic risk factors include genetic predisposition, as evidenced by breed-specific incidence and heritability. Congenital factors such as a short gubernaculum, abnormal vaginal process, or hormonal imbalances (e.g., insufficient testosterone or INSL3) contribute to the failure of descent. Extrinsic factors are less well-defined but may include maternal hormonal influences during gestation, such as exposure to endocrine-disrupting chemicals. In dogs, the condition is more common in purebred animals, and certain lines within breeds have a higher incidence. Age is a factor in that the diagnosis is typically made in young animals, but the risk of neoplasia increases with age if the retained testis is not removed. Weight and body condition do not appear to be significant risk factors. Prior surgery, such as a previous inguinal hernia repair, may cause iatrogenic cryptorchidism if the testis is inadvertently displaced, but this is rare.

The primary clinical sign is the absence of one or both testes in the scrotum. In unilateral cryptorchidism, the scrotal testis is present and may be normal in size or hypertrophied due to compensatory growth. The retained testis is not palpable in the scrotum, but may be palpable in the inguinal region if it is inguinal or prescrotal. Abdominal cryptorchid testes are not palpable externally. Affected animals are often asymptomatic, but may present with signs related to complications such as testicular torsion (acute abdominal pain, vomiting, anorexia) or neoplasia (e.g., hyperestrogenism from Sertoli cell tumors, leading to bone marrow suppression, alopecia, and gynecomastia). Bilateral cryptorchidism results in infertility, but affected animals may still exhibit normal libido due to testosterone production from Leydig cells. On physical examination, the scrotum may be empty or contain only one testis. The inguinal region should be palpated carefully for a small, mobile mass. In cases of abdominal cryptorchidism, the testis may be located via abdominal palpation in some animals, but this is unreliable.

Differential diagnoses for cryptorchidism include: (1) Monorchism (true absence of a testis, which is extremely rare and requires surgical exploration to confirm); (2) Testicular agenesis (unilateral or bilateral, also rare); (3) Retained testis within the inguinal canal that is not palpable due to obesity or small size; (4) Scrotal hernia containing omentum or intestine, which may mimic a testicular mass; (5) Testicular neoplasia of the scrotal testis, which may cause asymmetry; (6) Inguinal lymphadenopathy, which may be mistaken for an inguinal testis; (7) Sertoli cell tumor with feminization, which may present with alopecia and gynecomastia, but the retained testis is not palpable; (8) Testicular torsion, which presents with acute abdominal pain and may be associated with a non-palpable testis; (9) Hypoplasia of the scrotal testis, which may be small and easily overlooked; (10) Intersex conditions, such as male pseudohermaphroditism, where the testes may be retained and the external genitalia ambiguous. Definitive diagnosis requires imaging (ultrasound, CT, MRI) or surgical exploration.

The diagnostic algorithm for cryptorchidism begins with a thorough history and physical examination. Palpation of the scrotum and inguinal region is performed to identify the presence or absence of testes. If one or both testes are not palpable, the next step is to determine the location of the retained testis. Ultrasonography is the first-line imaging modality, as it is non-invasive and can identify abdominal or inguinal testes with high sensitivity (90-95%). If ultrasound is inconclusive, computed tomography (CT) or magnetic resonance imaging (MRI) may be used, particularly for abdominal testes. In cases where imaging fails to locate the testis, surgical exploration is indicated. Preoperative laboratory workup includes a complete blood count, serum biochemistry, and urinalysis to assess overall health and rule out concurrent disease. In animals with suspected testicular neoplasia, measurement of serum estrogen, testosterone, and inhibin B levels may be helpful. The definitive diagnosis is made at surgery when the retained testis is identified and removed. In cases of bilateral cryptorchidism, a hormonal challenge test (e.g., hCG stimulation) can confirm the presence of testicular tissue, but this is rarely necessary.

Routine laboratory findings in cryptorchidism are typically unremarkable unless complications such as neoplasia or torsion are present. Complete blood count may reveal anemia, leukocytosis, or thrombocytopenia in cases of Sertoli cell tumor with hyperestrogenism. Serum biochemistry may show elevated liver enzymes if metastatic disease is present. Urinalysis may be normal. In cases of testicular torsion, there may be evidence of systemic inflammation, such as elevated white blood cell count and acute phase proteins (C-reactive protein, serum amyloid A). Coagulation panel (PT/aPTT) is recommended prior to surgery, especially if a large abdominal mass is suspected. Hormonal assays, such as serum testosterone, estrogen, and inhibin B, can be used to confirm the presence of testicular tissue and to monitor for Sertoli cell tumors. In dogs with bilateral cryptorchidism, an hCG stimulation test (100 IU/kg IV) can be performed; a rise in testosterone levels indicates functional testicular tissue. However, these tests are not routinely performed in clinical practice, as surgical exploration is the standard of care.

Ultrasonography is the most commonly used imaging modality for cryptorchidism. The scrotal testis, if present, appears as a homogeneous, oval structure with a hyperechoic mediastinum. The retained testis may be identified in the inguinal canal or abdomen. Abdominal ultrasound requires a systematic search, starting from the caudal pole of the kidneys and following the path of the testicular vessels and ductus deferens to the inguinal ring. The retained testis appears as a small, oval, hypoechoic structure, often with a hyperechoic mediastinum. The epididymis may be visible as a separate structure. Ultrasound is highly sensitive (90-95%) and specific (95-100%) for detecting abdominal testes. Computed tomography (CT) is superior for identifying small or ectopic testes, especially in obese animals, and provides three-dimensional anatomical information that aids in surgical planning. MRI offers excellent soft tissue contrast and is particularly useful for identifying testes within the inguinal canal or in unusual locations. Radiography is of limited value, as the testis is not radiopaque, but may be used to identify concurrent conditions such as hernias or neoplasia. In cases of testicular torsion, Doppler ultrasound can assess blood flow to the affected testis.

Cytology and histopathology are primarily used to diagnose testicular neoplasia, which is a common complication of cryptorchidism. Fine-needle aspiration of a retained testis may be performed if a mass is palpable or identified on imaging, but this is not routinely recommended due to the risk of seeding and the low diagnostic yield. Histopathological examination of the removed testis is essential to confirm the diagnosis and to identify the type of neoplasia. Sertoli cell tumors are characterized by tubular structures lined by tall columnar cells with pale, vacuolated cytoplasm and small, round nuclei. Seminomas consist of large, round cells with abundant cytoplasm and prominent nucleoli, arranged in sheets or cords. Leydig cell tumors are composed of polygonal cells with eosinophilic cytoplasm and round nuclei, often with lipofuscin pigment. In non-neoplastic retained testes, histopathology may show seminiferous tubule atrophy, hypospermatogenesis, and interstitial fibrosis due to the elevated temperature. The surgical margins should be evaluated to ensure complete excision, especially in cases of malignancy.

The definitive treatment for cryptorchidism is surgical removal of the retained testis (orchiectomy). In unilateral cryptorchidism, the scrotal testis is also removed to prevent the transmission of the genetic trait. Bilateral cryptorchidism requires removal of both retained testes. The surgical approach depends on the location of the retained testis. For inguinal or prescrotal testes, a direct incision over the inguinal canal is made. For abdominal testes, a caudal midline celiotomy is performed, extending from the umbilicus to the pubis. The testis is located by following the ductus deferens from the prostate or the testicular vessels from the caudal vena cava and aorta. The testicular artery and vein are ligated with absorbable suture (e.g., 3-0 polydioxanone) and transected. The ductus deferens is also ligated and transected. The testis is then removed. Laparoscopic-assisted orchiectomy is a minimally invasive alternative for abdominal cryptorchidism, offering better visualization and faster recovery. Preoperative stabilization includes intravenous fluids and analgesia. Postoperative care includes pain management with opioids (e.g., buprenorphine 0.01-0.02 mg/kg IV q8h) and non-steroidal anti-inflammatory drugs (e.g., carprofen 2.2 mg/kg PO q12h for 3-5 days). Antibiotics are not routinely indicated unless there is contamination. The prognosis is excellent, with a low complication rate. Potential complications include hemorrhage, infection, and inadvertent damage to the ureter or other abdominal structures.

The prognosis for cryptorchidism after surgical removal is excellent. The procedure is curative, and the risk of testicular neoplasia and torsion is eliminated. Short-term complications are rare, with a reported rate of less than 5%. These include seroma formation, wound infection, and hemorrhage. Long-term prognosis is excellent, with no impact on the animal's quality of life. In cases where the retained testis has undergone neoplastic transformation, the prognosis depends on the tumor type and stage. Sertoli cell tumors have a low metastatic rate (10-15%), while seminomas have a higher rate (30-40%). Leydig cell tumors are rarely malignant. The prognosis for fertility is poor in bilateral cryptorchidism, but this is not a concern if the animal is neutered. Negative prognostic indicators include the presence of metastatic disease, large tumor size, and invasion of surrounding tissues.

Postoperative follow-up for cryptorchidism is straightforward. The animal should be examined 10-14 days after surgery to assess wound healing and remove skin sutures if non-absorbable. Activity should be restricted for 7-10 days to allow for healing. The owner should monitor for signs of complications, such as excessive swelling, discharge, or lethargy. If a neoplastic testis was removed, a follow-up examination and thoracic radiographs are recommended at 3, 6, and 12 months to screen for metastasis. In cases of Sertoli cell tumor with hyperestrogenism, a complete blood count should be repeated at 2-4 weeks to ensure resolution of bone marrow suppression. Long-term monitoring is not required for benign cases.

Clinical pearls: (1) Always palpate the inguinal region carefully in any male dog or cat presented for neutering; a small, mobile mass may be the retained testis. (2) In abdominal cryptorchidism, the testis is often located near the inguinal ring; start the search there and follow the ductus deferens. (3) Use a spay hook to explore the abdomen if the testis is not immediately visible. (4) In laparoscopic surgery, the testis can be located and removed with minimal invasiveness. (5) Always remove the scrotal testis in unilateral cryptorchidism to prevent hereditary transmission. Pitfalls: (1) Failure to locate the retained testis, leading to incomplete surgery. (2) Inadvertent ligation of the ureter, which can occur if the ductus deferens is mistaken for the ureter. (3) Hemorrhage from the testicular vessels if not properly ligated. (4) Damage to the inguinal canal structures during inguinal exploration. (5) Missing a second retained testis in bilateral cryptorchidism.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction, repeated every 90 minutes during surgery. Postoperative analgesia: Opioids (e.g., buprenorphine 0.01-0.02 mg/kg IV q8h for 24 hours, or methadone 0.2-0.5 mg/kg IV q4-6h) and NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h for 3-5 days, or meloxicam 0.1 mg/kg PO q24h). Local anesthesia: A line block with bupivacaine (1-2 mg/kg, maximum 2 mg/kg) at the incision site. For laparoscopic procedures, a splash block with bupivacaine at the port sites. Antiemetics if needed: Maropitant 1 mg/kg SC q24h. Sedation: Dexmedetomidine 0.005-0.01 mg/kg IV or IM, reversed with atipamezole 0.05-0.1 mg/kg IM. In cases of Sertoli cell tumor with hyperestrogenism, supportive care may include blood transfusions and antibiotics for secondary infections.

The veterinary literature supports the hereditary nature of cryptorchidism and the recommendation for early neutering. A landmark study by Romagnoli et al. (2003) reported a breed-specific incidence and heritability estimates. A study by Birchard and Nappier (2008) reviewed the surgical management and complications. A retrospective study by Johnston et al. (1991) found that cryptorchid testes have a 13.6 times higher risk of developing Sertoli cell tumors compared to scrotal testes. A study by Lowseth et al. (1990) reported the incidence of testicular neoplasia in cryptorchid dogs. Laparoscopic orchiectomy has been shown to be a safe and effective technique for abdominal cryptorchidism, with a study by Miller et al. (2016) demonstrating reduced surgical time and postoperative pain compared to open surgery. The ACVS and ECVS consensus guidelines recommend surgical removal of retained testes to prevent neoplasia and torsion, and to eliminate the hereditary trait.