|
CRYPTORCHIDISM (UNDESCENDED TESTICLES) IN THE HORSE
Overview
Cryptorchidism means "hidden testes" (crypt = hidden, orchid = testes), and is used to describe the condition in which one (unilateral) or both (bilateral) testicles do not descend normally. Common terms for animals with this condition include rig, ridgling, original, or high flanker. In a cryptorchid horse, one or both testicles, which form in the body, do not migrate into the scrotum. It may be retained anywhere from the abdomen to the inguinal canal, the normal passage route into the scrotum. Prevalence of left and right testicular retention is nearly equal, though retained left testes are more often in the abdomen while the right retained testicle is more often in the inguinal canal. Although a testicle is undescended, it still produces male hormones leading to characteristic stallion behavior. Unilateral cryptorchids are usually fertile; while bilateral cryptorchids are generally sterile. All breeds of horses may be exhibit cryptorchidism, but there is a higher frequency in Quarter Horses, Saddlebreds, Percherons, and ponies. The condition is considered heritable, so affected animals should be castrated to help prevent continuation of this congenital defect as well as for safety reasons.
Causes
A single cause of equine cryptorchidism has not been established, and contributing causes remain obscure. Based on available information, the condition is likely the result of a complex combination of genetic, hormonal, and mechanical factors. As indicated above, the condition is overrepresented in some breeds, supporting heritability of the condition, and many breed associations do not allow registration of cryptorchids.
Signs, Symptoms and Differential Diagnoses
Cryptorchid horses usually exhibit standard stallion behavior, but lack one or both scrotal testicles. Immature horses with the condition may be undetected until they are examined just prior to routine castration. Mature horses with no detectable testes that behave like stallions may be bilateral cryptorchids, unilateral cyptorchids with the descended testes removed, or geldings with stallion-like behavior. Monorchidism, complete absence of one testicle, is rare in the horse, and should only be considered after extensive testing and, potentially, surgical exploration.
Diagnosis
Typically, cryptorchidism can be diagnosed in horses with a clear history of no surgery by a combination of external and rectal palpation. Tranquilization allows deep external palpation of the inguinal canals as well as a thorough rectal exam, and will increase the chances that inguinal testes will drop down enough to be palpated. Additionally, ultrasonographic examination may be employed to locate a testicle within the abdomen or inguinal canal.
Diagnosis of cryptorchidism in horses with incomplete background information or absence of palpable testicles is typically accomplished with blood tests. The male hormone testosterone is measured in the blood before and after administration of human chorionic gonadotropin (hCG). Stallions and cryptorchids have higher levels of testosterone and levels of the hormone increase after hCG administration. Castrated horses have low levels of testosterone and levels do not increase with hCG. The test is approximately 95% accurate in identifying cryptorchids. A test that does not require hCG administration is blood levels of conjugated estrogen levels. Typically, levels are higher in horses with testicular tissue, and a single measurement can often identify cryptorchids. The test detects cryptorchids about 95% of the time, but is unreliable in horses younger than 3 years and in donkeys. Both tests should be performed if either is inconclusive.
Normal and Cryptorchid Development and Anatomy
Testicles normally develop inside the abdomen next to the kidney in the fetus. During normal development, each testicle descends through the inguinal canal to the scrotum, guided by a ligamentous structure called the gubernaculum. Just prior to or shortly after birth, the gubernaculum shortens, normal testicles descend to a permanent location in the scrotum, and rings at the base of the inguinal canal, called vaginal rings, permanently constrict, so that only the spermatic cord, the blood supply to the testicle, can pass through. In the cryptorchid, the testicle does not descend to its final place in the scrotum, but remains in the abdomen or the inguinal canal (Figure 1).
Figure 1. This photograph of an undescended testicle (black arrow) was taken during laproscopic surgery on a cryptorchid horse. The testicle is resting in the abdomen next to the inguinal canal (white arrow). In a normal horse, only the spermatic cord (black arrowhead) would be seen passing through the canal, and the testicle would be located in the scrotum.
Treatment Options
Treatment for cryptorchidism is surgical removal of both testicles. Removal of the normal testicle prior to removal of the cryptorchid testicle can complicate location of the cryptorchid testicle. Additionally, “hemi-castrated” horses retain their stallion-like behavior and reproductive capabilities, though a lack of identifiable testicles makes them appear like geldings. This creates a potentially dangerous situation. For these reasons, a normal testicle should never be removed prior to location and removal of the cyptorchid testicle.
There are two general surgical options for removal of undescended testicles, a standard surgical approach with the horse on its back under general anesthesia or a laparoscopic approach, often with the horse standing, but heavily sedated and the surgical area desensitized with local anesthetic. There several surgical approaches that may be used with the horse under general anesthesia. The approach used depends upon the preference of the surgeon and the location of the testicle based on the examination before surgery. All of the approaches require an incision, generally on the underside of the belly around the area of the scrotum. The testicle is located and manually removed from the abdomen or inguinal canal. A laparoscopic surgical approach requires the use of a camera and specialized equipment. With the horse standing, the abdomen is distended with sterile gas, and a camera is inserted into the abdomen through a small incision in the flank. Once the testicle is located, further small incisions are made to pass instruments into the abdomen and remove the testicle. With either approach, meticulous attention is paid to ensure that the blood supply to the testicle is securely closed off prior to removal to prevent potential bleeding.
Postoperative Care
Initial care after surgery usually consists of stall rest with hand walking. Unlimited exercise is gradually resumed after approximately 10 days to two weeks. Any sutures are typically removed around 7 days after surgery. Following laparoscopic surgery, the aftercare period is much reduced and horses can resume their activities after the first 72 hours. As with any castration procedure, appropriate handling and socialization measures should be taken after surgery. Though hormone levels dissipate almost immediately after testicle removal, learned behaviors often take a period of time and training to change.
Potential Complications Following Treatment
Complications are rare for cryptorchid surgery, but they may include anesthetic complications, excessive hemorrhage, bowel damage, infection, post-operative swelling, incision breakdown, and continued stallion behavior.
When to Seek Veterinary Surgical Advice
Identification and surgical removal of undescended testicles should be performed by a trained veterinary surgeon. The testicles are often smaller than normal and may not be formed correctly. Given the relatively large, crowded area in which they may be located, the job of finding and safely removing a wayward testicle can be a challenge. Surgeons trained according to the standards of the American College of Veterinary Surgery have specific knowledge and skills for diagnosis and treatment of cryptorchidism in the horse. Find an ACVS Veterinary Surgeon.
—Mandi Lopez, DVM, MS, PhD
Diplomate ACVS
Posted 8/18/2005
Updated by 6/16/2008 by Dr. Lopez
|
