A prostate ultrasound is a diagnostic test used to detect potential problems with a man's prostate. An ultrasound test involves very high-frequency sound waves that pass through the body. The pattern of reflected sound waves, or "echoes," shows the outline of the prostate. This test can show whether the prostate is enlarged, and whether an abnormal growth that might be cancer is present.
The prostate is a chestnut-shaped organ surrounding the beginning of the urethra in men. It produces a milky fluid that is part of the seminal fluid discharged during ejaculation. Prostate disorders are common in men over 50. In cases of prostate cancer , ultrasound is often crucial, since early detection, when the lesion is localized and curable, can lead to effective therapy.
A doctor may decide to do a prostate ultrasound following a digital rectal examination (DRE) that reveals any prostate abnormalities such as lumps or an enlarged prostate; or following a blood test that reveals abnormal levels of a substance called prostate-specific antigen (PSA), a normal protease produced by the prostate epithelium. Currently, testing for PSA is the best available tumor marker. Abnormal levels of PSA may indicate the presence of cancer. However, the PSA test is non-specific, and PSA can be elevated without the presence of prostate cancer.
The ultrasound procedure involves a special probe inserted into the rectum that sends sound waves to the prostate gland. The waves bounce off the prostate surface and are translated by computer as an image on a screen.
If cancer is suspected, the doctor will want to take a tissue sample (prostate biopsy ) to test it to see if it is cancerous. An ultrasound can show the location on the prostate from which the sample should be taken. It can also reveal if the cancer has begun to spread to other locations.
Ultrasound is also used in treatment of prostate cancer. If a doctor decides to treat the cancer with a surgical freezing procedure, ultrasound is used as an aid in the procedure. Doctors are also experimenting with a procedure that uses heat to kill cancerous prostate tissue. During this procedure, called high-intensity focused ultrasound (HIFUS), an ultrasound probe first creates an image of the prostate; then high-energy ultrasound beams target specific areas, generating heat that destroys cancerous tissue.
Ultrasound also can reveal such other types of prostate disease as prostatitis.
A prostate ultrasound study is generally not performed on men who have recently had surgery on their lower bowel. This is because the test requires placing an ultrasound probe about the size of a finger into the rectum.
Benign prostatic hypertrophy (BPH) —An enlargement of the prostate that is not cancerous. However, BPH may cause problems with urinating or other symptoms.
Doppler —In ultrasound, a technique used to detect and evaluate moving structures that is usually applied to the evaluation of blood flowing in vessels.
Prostate-specific antigen (PSA) test —A blood test to detect PSA, a substance that is often produced by cancers of the prostate.
Urethra —The tube through which urine passes from the bladder and is excreted outside the body.
The prostate ultrasound technique performed is called transrectal ultrasonography. This technique not only allows for visualization of the prostate; it is used to position the needle if a biopsy is performed. During the procedure, the cylinder-shaped ultrasound probe, or transducer, is gently placed in the rectum as the patient lies on his left side with the knees bent. This position allows for more comfort and easier insertion. The probe is rocked back and forth to obtain images of the entire prostate. Pictures of the prostate are produced and measurements are taken. The procedure takes about 15-25 minutes to perform. After the test, the patient's doctor can be notified right away, and usually he or she will have a written report within 36 hours.
During a biopsy, a small needle is inserted very rapidly into the prostate gland. Sample tissue is taken and sent to a pathology lab for preparation. Transrectal ultra-sound-guided core biopsy of the prostate is regarded as the most effective determinant of the grade, volume, and localization of a tumor and of its distribution within the prostate. Usually, six to eight biopsies are taken.
Recently, in an effort to improve prostate cancer diagnosis, physicians have performed experiments with ultrasound contrast-agent enhanced color Doppler imaging. By revealing increased vascularity associated with prostate cancer, the procedure can allow for more targeted biopsies, thus reducing the number of biopsies needed.
Patients are instructed to have an enema two to four hours before an exam. Feces or gas could impede the progress of the rectal probe. Patients also are instructed not to urinate for one hour before the test. If biopsies may be done, the doctor will prescribe an antibiotic that usually is taken in four doses, starting the night before the biopsy; the morning of the test; the evening after the test; and the following morning.
For the most part, transrectal ultrasound is a painless procedure. The patient may be warned that there could be some discomfort as the probe is inserted. Generally, the patient is allowed to leave after a radiologist or urologist has reviewed the results. There may be some mucus or a small amount of bleeding from the rectum after the ultrasound. Some patients notice a small amount of blood in the urine for up to two days after the test. Blood may also be present in the semen. As long as the amount of blood is small and resolves after one to two days, there is no cause for concern.
There are no serious risks from a prostate ultrasound study. Infection is rare and is probably a result of biopsy rather than the sonogram itself. If the ultrasound probe is moved too vigorously, some bleeding may continue for a few days.
Modern ultrasound techniques can display both the smooth-surfaced outer shell of the prostate and the core tissues surrounding the urethra. The entire volume of the prostate should be less than 20 milliliters, and its outline should appear as a smooth echo-reflecting (echogenic) rim. Some irregularities within the substance of the gland and calcium deposits are normal findings.
An enlarged prostate with dimmed echoes may indicate either prostatitis or benign enlargement of the gland, called benign prostatic hypertrophy (BPH). A distinct focal lump of tissue more likely means cancer. Cancer also often appears as an irregular area within the gland that distorts the normal pattern of echoes. In either case, a biopsy should clarify the diagnosis.
Health care team roles
The procedure is performed by a specially trained diagnostic medical sonographer. The sonographer assists the physician and radiologist in gathering sonographic data necessary to diagnose prostate cancer. Sonographers can have extensive, direct patient contact that may include performing some invasive procedures. The sonographer obtains and records patient history; performs diagnostic procedures and obtains diagnostic images; analyzes technical information; and provides an oral and written summary of technical findings to the physician for medical diagnosis. A urologist or radiologist performs the biopsy.
Medical sonography programs vary in length from one to four years depending on the program design and degree or certificate awarded. Program entry requirements vary as well, and range from a high-school diploma to specific qualifications in a clinically related health profession. Graduation from an accredited program is followed by a qualifying exam administered by the American Registry of Diagnostic Medical Sonographers (ARDMS). Continuing education is required.
Hagen-Ansert, Sandra L. Textbook of Diagnostic Ultrasonography, 5th ed. St. Louis, MO: Mosby, 2000.
Salmans, Sandra. Prostate: Questions You Have…Answers You Need. Allentown, PA: People's Medical Society, 1996.
Prostate Health Council. American Foundation for Urologic Disease. 1128 N. Charles St., Baltimore, MD 21201. 800-242-AFUD.
"Contrast Enhanced Color Doppler Imaging Improves Prostate Cancer Detection." Frontiers in Ultrasound, 1999. <http://www.auntminnie.com> (May 9, 2001).
Thompson, Richard B., and Ira M. Fielding. "A Retrospective Review of 2076 Prostate Ultrasonograms in One Urology Practice." The Permanente Journal, 2000. <http://www.kaiserpermanente.org/medicine/permjournal/winter00pj/frretro.html> (May 9, 2001).
Daniel J. Harvey