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Disease of the prostate gland is relatively common in dogs but less common in other species. Benign prostatic hyperplasia is by far the most common disease of the canine prostate. Bacterial prostatitis, prostatic abscesses, prostatic and paraprostatic cysts, and prostatic adenocarcinoma occur much less frequently. Although these disorders may produce clinical signs that include tenesmus during defecation, intermittent hematuria, recurrent urinary tract infections, and caudal abdominal discomfort, many dogs with prostatic disease are asymptomatic. Additional nonspecific signs, such as fever, malaise, anorexia, severe stiffness, and caudal abdominal pain, can occur with bacterial infections and neoplasia. Prostatic adenocarcinoma with bony involvement of the pelvis and lumbar vertebrae may cause hindlimb gait abnormalities. Less commonly, prostatic diseases may cause infertility or urinary incontinence. Prostatic adenocarcinoma may cause complete urethral obstruction.
Physical examination of the prostate gland should include abdominal and rectal palpation. An enlarged prostate typically is located further cranial than usual and can be found in the caudal abdomen, rather than within the pelvic canal. Size, shape, symmetry, consistency, mobility, and the presence or absence of pain are assessed by palpation. The normal dorsal sulcus (depression) aids in assessment of shape and symmetry.
Abdominal radiographs may help define the size, shape, and position of the prostate gland. The sublumbar lymph nodes, lumbar vertebrae, and bony pelvis should be evaluated radiographically for evidence of periosteal new bone and bony metastases. A positive-contrast retrograde urethrogram can be done when an abnormal prostate or paraprostatic cyst is difficult to differentiate from the bladder. Ultrasonography may provide additional information concerning echogenicity of the prostatic parenchyma and may identify focal prostatic lesions that cannot be palpated. Mass lesions within the prostatic urethra and discontinuity of the prostatic urethral wall are both highly suggestive of prostatic neoplasia.
Material for cytologic and microbiologic examination can be obtained by a combination of prostatic massage and urethral catheterization. Prostatic massage is easily performed; however, samples are routinely contaminated with urine from the bladder. Furthermore, prostatic massage may produce septicemia in dogs with prostatitis or a prostatic abscess.
Because prostatic fluid normally refluxes into the bladder, urinary tract infection is usually present with bacterial prostatitis. Microbiologic examination of the prostatic (third) fraction of the ejaculate is more accurate for assessment of prostatic infection than is examination of prostatic massage specimens when urinary tract infection is present. Neoplastic cells are often not recovered in specimens obtained by ejaculation or prostatic massage.
Fine-needle aspiration of the prostate gland can be performed transrectally or percutaneously, with or without ultrasonographic guidance; while generally safe and simple, this is not without some risk of penetration of surrounding structures. Biopsy is the most definitive, but also the most invasive, diagnostic procedure for differentiating prostatic diseases. Prostatic biopsy is probably best performed via celiotomy, although a skilled ultrasound radiologist may be able to safely obtain satisfactory biopsies.
Last full review/revision July 2011 by James A. Flanders, DVM, DACVS
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