Overview of Prostatic Diseases
Disease of the prostate gland is relatively common in intact dogs but less common in other domestic animal species. Benign prostatic hyperplasia is by far the most common disease of the prostate in intact male dogs. Bacterial prostatitis (acute or chronic), prostatic abscesses, prostatic and paraprostatic cysts, and prostatic adenocarcinoma are seen much less frequently and can be seen in castrated males. Depending on the disorder, clinical signs may include tenesmus during defecation, intermittent hematuria, recurrent urinary tract infections, and caudal abdominal discomfort. However, many intact males with benign prostatic hyperplasia (with or without chronic prostatitis) are asymptomatic or present with signs of hemospermia and/or infertility only. Additional nonspecific signs, such as fever, malaise, anorexia, severe stiffness, and caudal abdominal pain, can be seen with acute bacterial infections, abscesses, and neoplasia. Prostatic adenocarcinoma with bony involvement of the pelvis and lumbar vertebrae may cause hindlimb gait abnormalities. Less commonly, prostatic diseases may cause 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. Simultaneous abdominal and rectal palpation allows not only for the cranial aspects of the prostate to be palpated but also for better palpation per rectum because the prostate can be pushed into or near the pelvic canal, which is especially important in large-breed dogs and in males with very enlarged prostates. Size, shape, symmetry, consistency, mobility, and the presence or absence of pain can be 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. However, transabdominal ultrasonography is the best imaging modality for evaluation of the prostate, because it allows for evaluation of the prostatic parenchyma and adjacent soft-tissue structures. Increased echogenicity is associated with benign prostatic hyperplasia, chronic bacterial prostatitis, and prostatic neoplasia, whereas areas of mineralization may be secondary to chronic bacterial prostatitis or prostatic neoplasia. Mass lesions within the prostatic urethra and discontinuity of the prostatic urethral wall are both highly suggestive of prostatic neoplasia.
If the dog will not ejaculate, material for cytologic and microbiologic examination can be obtained by prostatic massage. Using aseptic technique, the bladder is catheterized, and all urine removed. The bladder is flushed with saline, and this sample is saved. The catheter is then withdrawn so that the end is caudal to the prostate. The prostate is subsequently massaged per rectum for about 1 minute to release prostatic fluid into the urethra, where it can be collected with the catheter. While occluding the urethral opening, saline is slowly injected. The catheter is then advanced into the bladder as aspiration is performed and another sample is collected. Results of cytologic and microbiologic examination from both prostatic wash specimens should be compared. Prostatic massage may produce septicemia in dogs with acute bacterial prostatitis or a prostatic abscess. 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 to differentiate prostatic diseases. To obtain diagnostic samples, prostatic biopsy should be performed via celiotomy or by a skilled ultrasonographer.