Page 564 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 539

VetBooks.ir most common DSD encountered in the horse. These fetus grows, resulting in enlargement of the ingui-
Male pseudohermaphroditism appears to be the
nal ring and canal. Traction of the gubernaculum,
individuals are 64XY with abdominally retained
testes and a poorly developed female tubular tract. abdominal pressure, elongation of the vaginal pro-
cess and enlargement of the inguinal ring together
Wide variations in the degree of virilisation of the result in descent of the testis into the scrotum. Fetal
tract and resulting phenotypic appearance have been gonadal androgen production, müllerian inhibiting
reported. These animals are generally female in substance and epidermal growth factor probably
appearance with stallion-like behaviour due to the also play a role in testicular descent. An hereditary
presence of abdominal testes. Other key features component in horses is likely, although the mode of
may include clitoromegaly and increased anogenital inheritance is disputed. It is possible that more than
distance. one genetic mode of inheritance for cryptorchidism
exists in the horse. A higher incidence of cryptor-
Diagnosis chidism occurs in the Standardbred, Quarter horse,
A presumptive diagnosis of DSD (intersex) can be Percheron, American Saddle horse, Paint horse and
made based on clinical signs (e.g. female-appearing Welsh Mountain pony than in other breeds.
animal exhibiting male behaviour; infertile stallion
with hypoplastic testes and penis) along with ambig- Clinical presentation
uous external and internal genitalia. Definitive In the case of unilateral cryptorchidism, visual
diagnosis requires karyotyping and additional inspection and palpation of the scrotum reveal only
cytogenetic analysis. The differential diagnoses for one testis. In bilateral cryptorchidism, no testes are
stallion-like aggressive behaviour, in an apparent palpable within the scrotum, the animal presents
female, includes ovarian granulosa-theca cell tumour with unwanted stallion-like behaviour and it may
and exogenous steroid (testosterone) administration. have been sold as a gelding. Cases of unilateral crypt-
orchidism, whereby castration of the single scrotal
Management/prognosis testicle has been performed, are unfortunately not
Surgical removal of retained testes and clitoridec- unusual. These animals typically present as apparent
tomy should solve behavioural issues and allow the geldings with stallion-like behaviour.
animal to be retained for performance or pleasure
purposes. Affected animals are usually sterile. Differential diagnosis
Differential diagnosis includes previous castration of
CRYPTORCHIDISM one or both testicles. A true anorchid or monorchid
condition can occur, but is very rare.
Definition/overview
Cryptorchidism is failure of normal descent of one Diagnosis
or both testes into the scrotal sac. The testis/testes Diagnosis of unilateral cryptorchidism is accom-
may be located inguinally, abdominally or subcuta- plished by inspection of the scrotum and care-
neously outside the scrotum. Testicular descent nor- ful palpation, together with ultrasonography, of
mally occurs between the last 30 days of gestation the scrotum and inguinal canal. The testis may be
and 6 months of age. retained within the inguinal canal or in the abdo-
men. Rectal palpation and transrectal/abdominal
Aetiology/pathophysiology ultrasonography are useful in locating the retained
The hormonal and physical events leading to tes- testis in the abdomen in many cases (Fig. 2.144).
ticular descent are not well understood. Elongation Diagnosis of bilateral cryptorchidism, or cases of
of the vaginal process, formed as an outpouch- unilateral castration of a scrotal testis with a retained
ing of the peritoneum, occurs due to the pull of abdominal testicle, is best accomplished with hor-
the gubernaculum on the tail of the epididymis. monal testing. A serum sample is taken for base-
Enlargement of the epididymal tail occurs as the line levels of testosterone and oestrogen. Baseline