equis - Articles
Testis: cryptorchidism
Synonym(s): Rig
Introduction
- Failure of testis(es) to descend fully into the scrotum.
- Classified according to location at time of diagnosis.
- Cause: unknown; heritable component; 2-4% of stallions are cryptorchid; left testis more often retained in the abdomen than right.
- Signs: none or only one testis palpable; failure of one or both testicles to descend in a young stallion; unexpected stallion behavior in a 'gelding'; reduced fertility or semen parameters.
- Diagnosis: palpation Urogenital: rectal palpation, rectal examination Musculoskeletal: rectal palpation, blood tests for estrone sulfate Endocrine: estrone sulfate assay or testosterone Endocrine: testosterone assay.
- Treatment: unilateral/bilateral castration Testis: castration - overview + unilateral/bilateral cryptorchidectomy Testis: cryptorchidectomy - inguinal / parainguinal Testis: cryptorchidectomy - flank Testis: cryptorchidectomy - suprapubic paramedian Testis: cryptorchidectomy - ventral midline approach.
- Prognosis: good for general health after surgery. Both testes should be removed when a retained testis is removed because the condition is hereditary. The horse will obviously be infertile once both testes have been removed.
Presenting signs
- Failure of one or both testes to descend into normal position in scrotum.
- Location of retained testis may be in the abdomen, inguinal canal or subcutaneous.
- Type 1: temporary inguinal retention.
- Type 2: permanent inguinal retention.
- Type 3: complete abdominal retention.
- Type 4: incomplete abdominal retention.
Geographic incidence
- Worldwide.
Age predisposition
- 1-3 years (at diagnosis).
- 4-9 years (at diagnosis).
- <1 year.
- >10 years.
Gender predisposition
- Male.
Breed/Species predisposition
- Percheron Percheron.
- American Saddle Horse Saddlebred.
- American Quarter Horse Quarterhorse.
- Ponies.
- Cross-bred horses.
- Shire Shire.
- Thoroughbred Thoroughbred.
- Arab Arab.
Cost considerations
- Surgical castration.
- Investigation.
Pathogenesis
Etiology
- Uncertain.
- Suggestions include:
- Improper function of the gubernaculum particularly regression.
- Genetic predisposition - complex and involves multiple genes.
- Abnormal fetal and/or maternal hormones.
- Combined with other congenital abnormalities such as intersexuality Reproduction: gonadal dysgenesis.
- Persistence of suspensory ligament of testis preventing migration.
- Failure of testicle to regress to a sufficiently small size to transverse the vaginal ring including testicular teratoma Teratoma.
Predisposing factors
General
- Cryptorchidism in sire.
- History of cryptorchidism in lineage of either parent.
- Other congenital or developmental defects.
- Cross-bred horses.
- Ponies.
Pathophysiology
- Failure of one or both testes to descend to scrotal position.
- Cause uncertain, may be genetic, hormonal or multifactorial.
- Note that the epididymis does not produce testosterone, and retention of epididymal tissue cannot account for persistence of stallion-like behavior Behavior: stallion.
- Usually unilateral (5-20 (15)% bilateral).
Normal descent of the testis
- Testes develop at the caudal pole of the kidney at approximately 5.5 weeks of gestation.
- Suspended by mesorchium (fold of peritoneum) from the dorsal abdominal wall.
- Attached to body wall by mesenchyme which becomes gubernaculum, which guides descent through the inguinal canal and then becomes the epididymal ligament.
- From 6 weeks of gestation the testicle increases rapidly in size and by 8 months is as large as an adult testicle.
- Descent begins at 270-300 days gestation.
- Epididymis enters the canal first as the gubernaculum grows and dilates the vaginal ring and canal.
- Increased fetal abdominal pressure helps push the testicle through the vaginal ring.
- The gubernaculum is within the scrotum and can be mistaken at birth for a testicle. This gradually reduces allowing complete descent of the testicle into the scrotum.
- Left testicle slightly larger than right on average with possibilities of increased left sided abdominal retention (75%) and right sided inguinal retention (60%).
- At birth about 50% of foals have descended testes.
- By 2 weeks after birth, the vaginal ring contracts preventing retraction of testicle from the inguinal canal back into abdomen.
- But descent into the scrotum may not be complete until 1 month (up to 4 years).
- Testicular descent after 6 months of age is rare.
Timecourse
- Some resolve spontaneously by the age of 3 years; others permanent.
Epidemiology
- May be a genetic predisposition.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Straticò P, Varasano V, Guerri G et al (2020) A retrospective study of cryptorchidectomy in horses: diagnosis, treatment, outcome and complications in 70 cases. Animals (Basel) 10 (12), 2446 PubMed.
- Hartman R, Hawkins J F, Adams S B et al (2015) Cryptorchidectomy in equids: 604 cases (1977-2010). JAVMA 246 (7), 777-784 PubMed.
- Brommer H, Grinwis G C M, Van Loon V & Ensink J M (2011) Laparoscopic-assisted diagnosis of anomalous unilateral abdominal cryptorchidism. Equine Vet Educ 23 (8), 391-395 VetMedResource.
- Raś A, Rapacz A, Raś-Noryńska M & Janowski T E (2010) Clinical, hormonal and ultrasonograph approaches to diagnosing cryptorchidism in horses. Pol J Vet Sci 13 (3), 473-477 PubMed.
- Barakzai S & Perkins J (2006) Equine cryptorchidism. UK Vet 11 (4), 5-9 VetMedResource.
- Rakestraw P (2006) The value of laparoscopy in equine cryptorchidism and monorchidism. Equine Vet Educ 18 (2), 88-89 VetMedResource.
- Mariën T et al (2001) Laparoscopic testis-sparing herniorrhaphy: A new approach for congenital inguinal hernia repair in the foal. Equine Vet Educ 13 (1), 32-35 VetMedResource.
- Parks A H, Scott E A, Cox J E & Stick J A (1989) Monorchidism in the horse. Equine Vet J 21 (3) 215-217 PubMed.
- Trotter G W (1988) Normal and cryptorchid castration. Vet Clin North Am Equine Pract 4 (3) 493-513 PubMed.
- Cox J E, Redhead P H & Dawson F E (1986) Comparison of the measurement of plasma testosterone and plasma estrogens for the diagnosis of cryptorchidism in the horse. Equine Vet J 18 (3) 179-182 PubMed.
- Hayes H M (1986) Epidemiological features of 5009 cases of equine cryptorchidism.Equine Vet J 18 (6) 467-471 WileyOnline.
- Wilson D G & Nixon A J (1986) Case of equine cryptorchidism resulting from persistence of the suspensory ligament of the gonad. Equine Vet J 18 (5) 412-413 PubMed.
- Cox J E, Edwards G B & Nea P A (1979) An analysis of 500 cases of equine cryptorchidism. Equine Vet J 11, 113 PubMed.