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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Any significant deviation (increase or decrease) in the size of the testes. This may be unilateral or bilateral.

Pathophysiology!!navigator!!

  • The testes and epididymides are positioned in a horizontal orientation and are freely movable within the scrotum
  • Changes in testicular size are often first noticed as a variation in scrotal size
  • Abnormal testicular size may be congenital or acquired
  • Testicular hypoplasia is the most common congenital abnormality
    • It may be associated with incomplete or delayed testicular descent (cryptorchidism)
    • Hypoplastic testes are hard, dense, and have poor or arrested spermatogenic activity
  • Acquired abnormal testicular size can be acute or progressive
  • Acute enlargement of a testis occurs after trauma, torsion of the spermatic cord, or orchitis/epididymitis. Testicular neoplasia may be seen in some cases of acute enlargement
  • Progressive enlargement of the testis is often due to testicular neoplasia
    • Seminoma, teratoma, Sertoli cell tumor, interstitial cell tumor
    • Of these, seminoma is the most frequently reported testicular tumor of the stallion
    • Most equine testicular tumors arise from germ cells, including seminomas and teratomas
    • The effect of neoplasia on testicular size (increase or decrease) may be insidious
  • Reduction of testicular size, testicular atrophy, is often a consequence of testicular degeneration
  • Testicular degeneration may arise from thermal injury, infection, trauma, vascular insult, hormonal disturbances, toxins, and age. Spermatogenesis is severely affected. Reduction or loss of fertility depends on the degree of compromise of spermatogenesis and whether the affection is bilateral or unilateral

Systems Affected!!navigator!!

  • Reproductive
  • Other systems (respiratory, gastrointestinal, lymphatic) may be affected subsequent to metastasis of primary testicular neoplasia

Genetics!!navigator!!

Cryptorchidism and testicular hypoplasia are suspected to have genetic components.

Incidence/Prevalence!!navigator!!

N/A

Geographic Distribution!!navigator!!

N/A

Signalment!!navigator!!

  • Intact male horses
  • Any age

Signs!!navigator!!

Historical Findings

  • Recent history of breeding or semen collection
  • Gross changes in the size of a testis
  • Reduced fertility
  • Pain (generally colic-like symptoms)
  • Reluctance to breed, jump, or walk

Physical Examination Findings

  • Increased or decreased scrotal size
  • Increased or decreased testicular size
  • Abnormal testicular texture (too soft or too firm)
  • Abnormal testicular position
  • Abnormal scrotal temperature (too warm or too cold)
  • Edema/engorged scrotum and/or contents
  • Derangements in systemic parameters (elevated heart rate, respiratory rate, inappetence, CBC abnormalities)

Causes!!navigator!!

  • Common causes of decreased testicular size
    • Cryptorchidism
    • Testicular degeneration, atrophy
  • Common causes of increased testicular size
    • Trauma (testicular hematoma, rupture)
  • Other causes of increased testicular size
    • Neoplasia (primarily seminoma)
    • Orchitis/epididymitis (bacterial infection, EIA, EVA, Strongylus edentatus infection, autoimmune)

Risk Factors!!navigator!!

  • Breeding activity
  • Systemic illness
  • Temperature extremes
  • Anabolic steroid use

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Differentiating Similar Signs

  • Scrotal enlargement due to scrotal hydrocele/hematocele and scrotal or inguinal hernia may be confused with testicular enlargement
  • US examination and measurement of the testes is the best means of differentiating the pathologies

Differentiating Causes

  • Duration of problem
    • Acute—traumatic injury, infection
    • Chronic—cryptorchidism, neoplasia, infection, testicular degeneration/hypoplasia
  • History of recent breeding and/or trauma
  • Palpation of the caudal ligament of the epididymis (attaches epididymal tail to caudal testis and aids in the determination of testicular orientation)
  • Testicular hypoplasia is usually congenital, while testicular degeneration is acquired
  • US (see Imaging)

CBC/Biochemistry/Urinalysis!!navigator!!

  • Inflammatory or stress leukocyte response
  • Eosinophilia may be an indicator of a parasitic infection
  • Increased fibrinogen in peripheral blood
  • Serum biochemistry profile and urinalysis are usually normal

Other Laboratory Tests!!navigator!!

  • EVA
    • Serum neutralization or complement fixation
    • Requires acute and convalescent serum samples
    • If stallion is seropositive, carrier state is determined with virus isolation
    • Semen is best sample for diagnosis (freeze portion of ejaculate and send to approved laboratory with serum samples)
    • Send samples to an approved laboratory
  • EIA
    • Agar gel immunodiffusion or ELISA, the Coggins test
  • Testicular degeneration
    • Endocrine profile (luteinizing hormone, FSH, testosterone, estrogens) from pooled samples obtained hourly for a minimum of 4 samples (due to pulsatile release of hormones)
    • Abnormal elevation of FSH and low total estrogen concentration are indicative of testicular degeneration

Imaging—scrotal/Testicular Us!!navigator!!

Testicular parenchyma should appear uniformly echogenic. Aberrations that may be identified by US include:

  • Rupture of the testis/tunica albuginea
    • Hypoechoic fluid accumulates in the scrotum with loss of discrete hyperechoic tunica albuginea around testicular parenchyma
    • Hypoechoic appearance of contents will gradually be replaced with echogenic densities as fibrin clots form
  • Engorgement of the pampiniform plexus and/or testicular congestion with torsion of the spermatic cord
    • Doppler can verify loss of blood flow to the testis
  • Loss of homogeneity in testicular parenchyma with neoplasia
    • Neoplasia results in heterogeneity (usually a circumscribed area) in testicular parenchyma
    • May see areas of increased or decreased echogenicity or be variable throughout

Other Diagnostic Procedures!!navigator!!

  • Needle aspirate and cytology—diagnose and/or differentiate recent hemorrhage or neoplasia
  • Testicular biopsy (histopathology)—diagnose and/or differentiate neoplasia and testicular degeneration/hypoplasia
  • Semen evaluation is useful in the diagnosis of testicular degeneration or hypoplasia:
    • Oligospermia
    • Azoospermia
    • Presence of round spermatids (spheroids)

Pathologic Findings!!navigator!!

  • Testicular hypoplasia—round, small diameter seminiferous tubules, spermatogenic arrest
  • Testicular degeneration—large, collapsed seminiferous tubules, vacuolization, poor or incomplete spermatogenesis
  • Testicular neoplasia—depends on neoplasm

Treatment ⬆ ⬇

Outline

TREATMENT

Treatment is directed at the cause of testicular abnormality.

Appropriate Health Care!!navigator!!

Inpatient versus Outpatient

  • Most causes of testicular enlargement require hospitalization for treatment/resolution
  • Horses with testicular degeneration that are not systemically ill may be managed on the farm
  • Horses with hypoplastic testes can be managed on an outpatient basis

Nursing Care!!navigator!!

  • Cold therapy (cold packs, ice water baths, water hose/hydrotherapy) is indicated for acute orchitis/epididymitis
  • Cold therapy sessions should not exceed 20 min and can be repeated every 2 h
  • Sexual rest is indicated in most cases until resolution of the problem
  • Administration of IV fluids is dependent on the systemic status of the horse

Activity!!navigator!!

Restriction depends on the cause of the testicular aberration.

Diet!!navigator!!

Modification is necessary only with cases of secondary ileus or as a preoperative consideration.

Client Education!!navigator!!

  • Fertility may permanently be lowered
  • Testicular degeneration results in various degrees of reduction in ejaculate quality
  • Testicular hypoplasia is a permanent condition
  • Horses with neoplasia should be examined carefully for evidence of metastatic tumor growth
  • Compensatory sperm production may occur in the remaining testis of a horse undergoing hemicastration
  • Serial semen evaluations are beneficial to monitor the fertility status of horses following testicular insult and treatment
    • Semen should be evaluated 75–90 days after complete resolution of testicular insult

Surgical Considerations!!navigator!!

Hemicastration is the treatment of choice for:

  • Torsion of the spermatic cord, if the duration of vascular compromise has caused irreversible damage and/or gonadal necrosis
  • Testicular rupture
  • Unilateral neoplasia or any condition causing irreparable damage to testis/es

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Anti-inflammatory therapy (phenylbutazone 2–4 mg/kg PO or IV BID or flunixin meglumine 1 mg/kg IV BID) is indicated in most cases
  • Antibiotic therapy should be considered in cases of orchitis/epididymitis and testicular trauma
  • Tetanus toxoid should be administered after testicular trauma and/or prior to surgery
  • Antiparasitic therapy for Strongylus edentatus infection (ivermectin 0.2 mg/kg PO every 30 days until resolution of lesions)

Contraindications!!navigator!!

N/A

Precautions!!navigator!!

N/A

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Semen collection and evaluation 90 days after complete resolution of testicular problem and/or surgery.

Possible Complications!!navigator!!

  • Infertility/subfertility
  • Endotoxemia
  • Laminitis
  • Scrotal adhesions
  • Death

Expected Course and Prognosis!!navigator!!

Dependent on etiology.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Cryptorchidism is commonly associated with testicular hypoplasia
  • Male equine hybrids (mules or hinnies) often have hypoplastic testes

Age-Related Factors!!navigator!!

  • Prepubertal testes are small and can be misdiagnosed as pathologically hypoplastic
  • Testicular growth increases rapidly from 12 to 24 months of age in horses
  • Testes may take 4–5 years to reach full size and maturity

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

N/A

Abbreviations!!navigator!!

  • EIA = equine infectious anemia
  • ELISA = enzyme-linked immunosorbent assay
  • EVA = equine viral arteritis
  • FSH = follicle-stimulating hormone
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Blanchard TL, Johnson L, Roser AJ. Increased germ cell loss rates and poor semen quality in stallions with idiopathic testicular degeneration. J Equine Vet Sci 2000;20:263–265.

Brito LFC, Englis JB, Turner RM, et al. Bilateral testicular mixed germ cell-sex cord-stromal tumours in a stallion. Reprod Dom Anim 2009;44:846–851.

Govaere J, Ducatelle R, Hoogewijs M, et al. Case of bilateral seminoma in a trotter stallion. Reprod Dom Anim 2010;45:537–539.

Pearson LK, Rodriguez JS, Tibary A. How to obtain a stallion testicular biopsy using a spring-loaded split needle biopsy instrument. Proc AAEP 2011;57:219–225.

Turner RM, Zeng W. The emerging pathophysiology of age-related testicular degeneration with a focus on the stallion and an update on potential therapies. Reprod Dom Anim 2012;47(Suppl. 4):178–186.

Author(s) ⬆

Author: Ahmed Tibary

Consulting Editor: Carla L. Carleton

Acknowledgment: The author and editor acknowledge the prior contribution of Margo L. Macpherson.