- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- Failure of 1 or both testes to descend completely into the scrotal sac
- Affected males are referred to as rigs, ridglings, originals, or, if the testis is located in the inguinal canal, high flankers
- Complete abdominal cryptorchid—when the testis and entire epididymis are contained within the abdomen
- Incomplete abdominal cryptorchid—when the testis and most of the epididymis are intra-abdominal but the ductus deferens and cauda epididymis (i.e. tail) are located in the inguinal canal
- Inguinal cryptorchid—when the testis is located in the inguinal canal
- Ectopic cryptorchid—when the testis is subcutaneous and cannot be displaced manually into the scrotum
- Embryologically, testes develop adjacent to the kidneys and are situated in the dorsal abdomen. Both testes descend ventrally through the abdominal cavity and inguinal canals into the scrotum sometime during the last 30 days of gestation or first 10 days after birth
- Failure of the testes to descend may result from abnormal development or function of the gubernaculum, failure of the fetal testis to regress in size and allow it to pass through the vaginal ring into the inguinal, or insufficient intra-abdominal pressure
- Cryptorchidism has been associated with failure to produce insulin-like peptide 3, testosterone, and/or their respective receptors
- Cryptorchidism is commonly unilateral, although up to 15% of cases are bilateral. The ratio of inguinal to abdominal testis retention varies from one study to another and may reflect differences in horse populations. Some studies report a higher incidence of abdominally retained left testes
- Spermatogenesis is arrested at the spermatogonia stage in the abdominally retained testis. If testes are retained in the inguinal canal, development may proceed to the primary spermatocyte stage
- Unilateral cryptorchids have normal fertility while bilateral cryptorchid stallions are sterile
- Cryptorchidism has been associated with increased incidence of testicular tumors
- Cryptorchidism is suspected to be a heritable condition in some breeds, but scientific evidence on the mode of heritability is lacking
- Heritability of cryptorchidism was estimated to be 0.12–0.35 in Icelandic horses
- All breeds
- Absence of a palpable testis in the scrotal sac by 1 month of age is presumptive evidence of cryptorchidism. After 12 months, inguinal retained testes rarely enter the scrotum but, reportedly, have entered in horses as old as 2–3 years of age
- Unilateral is ≅10-fold more prevalent than bilateral
- The left testis is retained slightly more often than the right in horses
- Left testes more often are intra-abdominal; right testes are equally likely to be inguinal or abdominal
- Stallion-like behavior in presumed geldings
- Rarely associated with pain or other signs of disease
- Isolated reports of torsion of the retained testis and of intestinal strangulation in association with a retained testis
- Cause unknown
- Genetic research suggests a complex mechanism of inheritance involving several genes. The decreasing incidence of cryptorchidism in certain lines of horses suggests that selective breeding influences the incidence
- Both autosomal dominant and autosomal recessive modes of inheritance have been proposed
- In addition to genetics, other factors implicated in abnormal testicular descent include inadequate gonadotropic stimulation, intrinsically defective testes, and mechanical impediment of descent, all of which may, in turn, have a genetic basis
- Cryptorchidism has been associated with intersexuality and abnormal karyotypes
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS