Page 565 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

540 CHAPTER 2

VetBooks.ir 2.144 reliable. Recently, the development of an assay for
anti- müllerian hormone (AMH) has proven useful
for diagnosis of cryptorchidism. AMH concentra-
tions were shown to be significantly higher in crypt-
orchids and intact stallions compared with geldings,
where they are essentially undetectable. Due to
considerable interlaboratory variation, practitioners
should interpret the test using the reference intervals
supplied by their laboratory.

Management
Surgical exploration and removal of the retained tes-
tis results in rapid improvement of unwanted stal-
lion-like behaviour. The method chosen for surgical
removal of the retained testicle depends largely on
the location of the testicle and the preference of the
surgeon. The most common approaches include the
inguinal, parainguinal and laparoscopic (standing or
recumbent) methods:

• The inguinal approach allows exploration
of both the inguinal and abdominal cavities
during surgery. With this method, the animal
Fig. 2.144 Transrectal ultrasound appearance of the is anaesthetised and aseptically prepared. An
retained abdominal testis in a cryptorchid horse. incision is made either over the scrotal sac or
directly over the inguinal ring. The epididymis
and/or testicle are located by blunt dissection
testosterone values ≤0.83 nmol/l [0.24 ng/ml] indi- of the inguinal ring. If the testis in not found,
cate absence of testicular tissue, while baseline val- the surgeon places gentle traction on the scrotal
ues ≥1.53 nmol/l [0.44 ng/ml] indicate presence of ligament (gubernaculum) until the vaginal
testicular tissue and no further testing is necessary process is found. The tail of the epididymis is
If levels are low and stallion-like behaviour persists, attached to the vaginal process and once found,
or when values fall between 0.83 and 1.53 nmol/l gentle traction on this structure will expose the
[0.25 and 0.44 ng/ml], a hormonal stimulation test is testis for removal.
recommended. Following a serum sample for base- • In the parainguinal approach, an incision is made
line levels, 5,000–10,000 IU of hCG is administered several centimetres medial to the inguinal ring.
intravenously. Follow-up samples are recommended In addition, some surgeons use a pararectal
1 hour, 2 hours and 24 hours later. A significant rise or midline approach in appropriate cases. The
(4–20 times) above baseline levels following hCG surgeon’s hand is introduced into the abdomen
administration indicates the presence of testicular and the testicle located and removed.
tissue. The addition of a total oestrogens assay to • If laparoscopic equipment is available, laparoscopic
the testing panel may improve diagnostic accuracy surgery may be undertaken. This method has
in mature animals. An oestrogen or oestrone sul- the advantages of reduced patient recovery
phate test alone is not recommended for colts less time, direct visualisation of the testicle and any
than 3 years of age or donkeys of any age, as false haemorrhage, and closure of the abdominal wall,
negatives are common. An hCG stimulation test thereby reducing the chance of postoperative
for both testosterone and oestrogen will be more herniation. The procedure can be carried out