Prostatomegaly (Enlarged Prostate)

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Prostatomegaly (Enlarged Prostate)

By: Dr. Douglas Brum

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Section: Diagnosis In-depth

A complete history and physical examination is the first step of obtaining an accurate diagnosis. It is very important to note if the dog is neutered or intact, as this will affect the diagnostic plan. A rectal exam is always indicated. Depending on the prostate's size and dog's conformation, the prostate (or part of the prostate) is usually palpable rectally. The size, shape, and texture of the gland are noted.

Prostatomegaly is much more common in intact older dogs. Many times the enlarged prostate is picked up as an incidental finding on the physical exam. If the prostate is smooth, not painful, symmetrically enlarged and the dog is not showing any clinical signs, the diagnosis of BPH is presumed, and no further work-up is recommended. In dogs neutered at a young age, the symptom of prostatomegaly should be investigated more aggressively.

The following tests may be indicated in some dogs having prostatomegaly:

A urinalysis to detect inflammatory changes or blood in the urine and to evaluate prostatic disease. The urine should be a sterile specimen for accurate interpretation. Animals with prostatitis or abscesses may show signs of infection (increased white blood cells and bacteria) in the urine. Some dogs with chronic intermittent bladder infections have underling prostatitis as the primary cause of the problem. A normal urinalysis does not preclude a diagnosis of prostatic disease.

A culture and sensitivity of the urine to determine if a bacterial infection is present. A positive growth of bacteria indicates that a urinary tract infection is present. However, the results are not specific for a prostatic infection as an infection anywhere along the urinary tract (bladder, kidneys or prostate) may give positive results. Additionally, dogs with prostatic infections may not have any bacterial growth on culture as the bacteria may be sequestered deep within the prostate and not be present in the urine at the time of sampling. A bacterial culture and sensitivity needs to be interpreted with caution and should be evaluated in light of the total clinical presentation of the animal.

Cytologic (microscopic) evaluation of seminal fluid. Samples are obtained via an ejaculate and the fluid is checked for evidence of infection, blood or tumor cells. The sample, ideally the third fraction of the ejaculate, can also be cultured if indicated. Dogs with BPH have normal seminal fluid with or without blood. This test is not often done, since obtaining a sample may be difficult, especially with an ill, painful or uncooperative patient.

A prostatic massage and wash. There are several techniques for obtaining this sample. Briefly, a urinary catheter is passed to the level of the prostatic urethra and the prostate is digitally massaged through the rectum. A sample is obtained by flushing fluid into the area and then aspirating the fluid back through the catheter. The sample is then submitted for cytology and culture. Dogs with BPH have normal results.

Abdominal radiographs are very useful in evaluating the abdominal organs and the extent of prostatic enlargement. The general size and shape of the prostate is noted, and the lymph nodes that drain the prostate are evaluated for enlargement. With prostatic enlargement the colon may be pushed upward and compressed, while the bladder may be pushed further into the abdomen. Large circular masses adjacent to the prostate may indicate paraprostatic cysts or a large abscess. If there is poor abdominal contrast in the area of the prostate an abscess, tumor or cyst may be suspected. Abnormal calcification of the prostate is easily visualized radiographically and sometimes correlates with a neoplastic process. Infection can also cause these changes. The bones, especially the lumbar vertebral bodies may show evidence of metastatic spread in cases of prostatic neoplasia.

An abdominal ultrasound to evaluate the texture and consistency of the prostate, as well as size and shape. Cysts and abscesses are easily visualized. Changes in texture (echogenicity) can be seen with any type of prostatic disease. Abdominal lymph nodes are observed for enlargement. In order to obtain a more specific diagnosis, an area that is identified as abnormal may be aspirated or biopsied using the ultrasound for guidance.

Fine needle aspiration is useful in collecting fluid from cysts or obtaining small cell samples from the prostatic tissue. A biopsy provides a core of tissue for histopathology (microscopic examination of tissue), and usually provides more accurate information about the pathology of the prostate, since a larger amount of tissue can be evaluated. The ultrasound appearance of a dog's prostate with BPH generally shows a smooth capsule (covering) with the gland symmetrically enlarged. Small cystic areas may be noted that are usually well defined and have smooth margins. Biopsy is the only way to diagnose BPH definitively, but most times is not performed if the clinical presentation and history are typical.

Occasionally a clotting profile is indicated if there is significant bloody discharge from the penis or blood in the urine. Potential clotting abnormalities that might cause blood to be present in the urine include immune mediated thrombocytopenia and rodenticide intoxication. If the prostatomegaly is caused by excessive circulating estrogen, the platelet count might be decreased due to bone marrow suppression by the high estrogen levels. Clotting tests to be considered might include an activated clotting time (ACT), a prothombin time (PT), activated partial thromboplastin time (APTT), platelet count, and possible a von Willebrands (VWF) test.

CBC. The CBC is a useful test to run in cases of pathologic prostatomegaly as it evaluates the red and white blood cells. Elevations in total white count can be seen in inflammatory conditions associated with prostatic infection or neoplasia. Anemia, assessed by a low red blood cell count, may be seen in chronic prostatic disorders. The anemia seen in prostatic disease is generally low grade and not severe, unless it is associated with squamous metaplasia and excessive estrogen blood levels. Testicular Sertoli cell tumors are the most common tumor to produce estrogen and cause these changes.

Biochemical profile. The biochemical profile evaluates the metabolic status of a variety of organ systems. Since prostatomegaly is a more common occurrence on older animals, it is a useful screening test to rule out other problems and or associated disease. Liver values may be elevated with the spread of prostatic neoplasia or by septicemia. If the prostate or an associated prostatic cyst or abscess were causing a urinary obstruction, the kidney values would be elevated, indicating an emergency situation. Blood sugar and electrolytes are also checked to provide a good overall assessment of the general condition of the patient. In dogs with acute prostatitis, or sepsis, hypoglycemia (a low blood sugar) may be seen.

Thoracic radiographs. X-rays of the chest are indicated any time prostatic neoplasia is suspected. Thoracic radiographs may show evidence of tumor spread to the lungs. Unfortunately if prostatic cancer is present, and even if the chest films are clear of visible tumors, there is still a reasonable chance that the cancer has spread.

Distention retrograde urethrocystography. Occasionally the abdominal X-rays may provide ambiguous results as to the nature of the prostatomegaly, especially if a large prostatic abscess or paraprostatic cyst is present. Distention retrograde urethrocystography is a technique where dye and air are injected through the urethra and into the bladder. This technique allows the urethral lining to be visualized, and better defines the bladder, prostate and any associated mass lesions that may be present.

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