Page 523 - WSAVA2018
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S. Romagnoli1
1Department of Animal Medicine, Production and Health, University of Padova, Agripolis, Legnaro, 35020 (PD), Italy
Normal prostatic development and function
The prostate gland is the major accessory sex gland
in the male dog. It is located just caudal to the bladder
in the area of the bladder neck and proximal urethra.
Its purpose is to produce prostatic fluid as a transport and support media for sperm during ejaculation. Basal prostatic secretion is constantly entering the prostatic excretory duct and prostatic urethra. In the absence
of micturition or ejaculation, urethral pressure moves prostatic fluid cranially into the bladder (a mechanism called prostatic fluid reflux). As the dog grows old the prostatic parenchyma is characterized by an increase
in epithelial cell numbers (hyperplasia) as well as an increase in epithelial cell size (hypertrophy), but the increase in cell number is more marked1. This growth process begins as glandular hyperplasia in dogs as young as 2.5 years of age2. Intraparenchymal fluid
cysts may develop in association with hyperplasia.
Such cysts are variable in size and contour, contain a thin, clear to amber fluid and, if intraprenchymal, may communicate with the urethra thus leading to intermittent haemorrhagic or clear, light yellow urethral discharge.
Benign Prostatic Hyperplasia
Due to normal growth and glandular hyperplasia, the prostate of intact normal male dogs increases in weight, for the first 5 years, with a peak at 4 years of age1.
As many as 16% of dogs have been reported to have histologic evidence of benign prostatic hyperplasia (BPH) by 2 years of age2. The incidence of BPH increases to over 80% with advanced age. Senile involution of the prostate occurs in animals aged 11 years or more1. Like
in humans, the prostate of a mature dog is chronically dependent upon a continuous supply of androgen to maintain its appropriate cell content and functional activity. In particular, prostatic growth and secretion are modulated by 5-alpha-dihydrotestosterone (DHT) that is the active androgen at intracellular level.
The regulation of prostatic content of DHT is determined by the relationship between the rate of production and removal of this steroid in the prostate gland itself rather than by DHT blood levels. Normally, it is adequate to maintain a balance between prostatic cell loss and renewal such that neither involution nor proliferative overgrowth of the gland occurs. In both canine and human BPH, this balance is increasingly being shifted
in favour of a large net increase in the total number of prostatic cells with advancing age. In addition, it has
been well documented that, even in young dogs, the experimental development of BPH can be induced simply by treatment of animals for 3-4 months with androgen and, in this regard, several androgens have been tested for their potential abilities to induce this disorders. One of the most serious consequence is due to the presence of fluid-filled cysts making the prostate susceptible to infection from bacteria ascending the urethra as accumulated prostatic fluid is an excellent media for bacterial growth3. Hematogenous spread of bacteria and spread from the kidneys and bladder via urine or from the testicles and epididimys via semen can also occur. Bacterial prostatic infection can be acute and fulminant or chronic and insidious leading to abscessation4.
The hyperplastic prostate is highly vascularized and therefore the gland bleeds easily, which explains the common clinical sign of blood from the tip of the penis or blood in the urine. Blood loss in the prostatic urethra can be so intense that the ejaculate may appear completely red. Although presence of blood in the semen is typically considered to be a cause for infertility, dogs with blood in their ejaculates may be fertile. The reason for BPH being a common cause of infertility in the dog is probably due to the alteration of the biochemistry of the prostatic
fluid whose important action of nutrition of spermatozoa is decreased. Prostatitis or abscessation are likely consequences of presence of blood in the prostate4.
Diagnosis of canine BPH
BPH is diagnosed based on history (bloody penile discharge, difficulties in defecation/urination, poor semen quality and infertility, absence of haematological/ biochimical alterations), physical exam and abdominal ultrasound (increase in prostatic size, presence
of prostatic cysts), and if necessary a fine needle aspirate3,4,5. Urinalysis helps to rule out urinary tract diseases as a cause of penile discharge (cystitis should be treated prior to onset of BPH therapy to avoid confounding factors in the interpretation of results).
An enlarged, hypertrophic prostate may cause blood dripping from the tip of penis (the most common clinical sign), or it may grow and expand in the rectal canal, causing tenesmus and sometimes difficult defecation (less common) 6. Other than the above signs, affected dogs are usually normal and the prostate on palpation is non-painful, symmetrically enlarged and with variable consistency. Urine may contain blood (gross or microscopic). If hyperplasia is accompanied by urethral discharge, this is typically haemorrhagic or clear but not purulent.
Prostatic enlargement may be also visualized on abdominal radiography as causing dorsal displacement of the colon and cranial displacement of the bladder5. On retrograde urethrocystography the prostatic urethra may be normal or narrowed and undulant with mucosal
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