One of the conundrums of
reviewing diseases from the perspective of a surgical pathologist is that the
prevalence of diseases as represented by the submission of biopsies, is very
different from the prevalence seen by clinicials or theriogenologists (who are also clinicians!). The bias here
will be toward what you will see as a pathologist, but many diseases simply are
not biopsied. The listing of diseases are done with the view to
the clinical prevalence!
Vasculitis of testicular, deferential
and cremaster arteries may be found in malignant catarrhal
fever and bovine viral diarrhea virus infection of bulls. Apparent hypoplasia of veins of the spermatic
cord is reported in bulls with thickening and degeneration of the testicular
artery.
Although studies in the bull have not demonstrated a direct
connection between venous and arterial blood vessels of the pampiniform
plexus, functional arteriovenous
anastomoses through small vessels do occur in normal bulls, boars, and
rams, and may represent a further means of thermoregulation of the testis. A
large anastomosis of the spermatic artery and vein is reported in a stallion
with an abdominal testis.
Directional deviations of the erect penis occur with persistence
of balanopreputial folds – regions where the prepuce failed to separate from the penile
epithelium. A well known fold is the persistent penile frenulum, which occurs
when the penile frenulum fails to separate from the prepuce. Persistent penile
frenulum is reported in the bull, boar, buck, dog, and cat. Although studies in
the boar have indicated some breed susceptibility for persistent frenulum,
there is no definite evidence for inheritance of this trait in any domestic
species. Deviation of the penis
occurs with asymmetrical development of the cavernosum
of the penis in the horse and donkey, malfunction of the apical ligament in the
bull and ram, and congenital curvature of the os
penis in the dog.
Erectile dysfunction,
failure of erection of the penis, is
rare. Erection requires central nervous system control, local nervous control
with contraction of the ischiocavernosus muscles and
vasoconstriction of veins. This allows arterial input to the erectile tissue of
the cavernosum and spongiosum
but occludes venous drainage. Vascular defects of the penis that cause failure
of erection are studied in the bull and boar, but their precise diagnosis antemortem or postmortem requires
injection of contrast material and radiography, or injection of plastic into
vessels to form casts. Vascular shunts
from the cavernosum to the spongiosum
of the penis or to peripenile vasculature prevent
effective erection. Congenital shunts from the cavernosum
to neighboring veins in boars can be inherited. Immunohistochemical studies of
impotence in the boar provided evidence that defective innervation contributes,
with depletion of vasointestinal polypeptide (VIP)
reactivity in penile nerves.
Penetrating injuries and traumatic fistulas of the erectile
tissue and the urethra or external tissues leads to hemorrhage that can be life
threatening. This, in the bull, includes forced deviation and rupture of the
penis with subsequent hematoma formation. Penile hematoma resulting from forced
deviation of the penis occurs in bulls and rams at the distal bend of the
sigmoid flexure, but sometimes proximal to it (Fig 5.59). In stallions, rupture
of the cavernosum outside an intact tunic (tunica albuginea) of the penis is more frequent; trauma is the
likely cause. Other vascular lesions include varicosities of preputial veins in
stallions that may lead to thrombosis, edema, and inflammation. In dogs, trauma
to the cavernosum or root of the penis may occur
during attempted copulation and results in hindquarter pain and/or lameness,
dysuria, and perineal edema but no obvious hematomas.
Extensive thrombosis of the corpus cavernosum penis occurs
in stallions, dogs and cats with priapism, and it was unclear whether the
thrombi were the cause or result of pain and persistent erection. In separate
stallions, concurrent nematodiasis and metastatic
melanoma were considered the primary cause.
Eversion of the
preputial mucosa as a temporary event is common in bulls. Bos indicus bulls
develop prolonged eversion as many have inadequate muscules
in the prepuce. Trauma to the everted epithelium and
desiccation lead to edema and inflammation (Fig 5.60).
A preputial
diverticulum is anatomically normal in the boar but abnormal in other
species, such as the bull and water buffalo. Deflection of the penis into the
diverticulum by boars results in accumulation of debris, urine, and semen that
predispose to local infection and inflammation.
Tearing of preputial mucosa,
typically at the ventral preputial fornix, is a common injury that occurs in
bulls used for artificial insemination. The precise cause is unknown.