Transrectal Ultrasound (TRUS)
TRUS is no longer recommended as a screening test for prostate cancer, but it is useful when either a DRE or a PSA test is suspicious. A probe about the size of the index finger is inserted into the rectum. It emits sound waves that bounce off the prostate gland, producing echoes that a computer uses to create a picture of the prostate. This picture, called a sonogram, can show abnormal areas, including tumors, within the prostate. Prostate tumors and normal prostate tissue tend to reflect sound waves differently, so the test can be used to see possible tumors that are too small to be palpated in a DRE. However, only about one-half of cancers larger than 1 cm, thus thought to be significant, are seen on ultrasound. And most abnormalities seen on an ultrasound are not cancer. This is why TRUS is not used to screen for prostate cancer. TRUS is useful for guiding the biopsy needle if a biopsy is deemed necessary. Placing the TRUS probe into the rectum may be temporarily uncomfortable, but the procedure itself is essentially painless. The TRUS examination is done in a doctor's office or outpatient clinic and usually takes only about 10 to 20 minutes.
TRUS is a radiologic method of imaging the prostate to detect potentially cancerous abnormalities. TRUS involves placing an ultrasound probe about the size of the index finger into the rectum. The probe is a highly sophisticated instrument that works like sonar, emitting sound waves that bounce off tissue and return to the probe. The sound waves create an image of the prostate, which a urologist or ultrasonographer interprets. Because only 3 mm of tissue separate the rectum from the prostate, the transrectal probe is ideally positioned to view the prostate. TRUS is used:
- as a diagnostic tool to detect otherwise unsuspected prostate cancers
- to locate abnormal, potentially malignant areas in a person with an already elevated PSA level or an abnormal DRE; the TRUS is used to pinpoint the nodule's exact location and assess its size and character
- to guide the biopsy needle to systematically sample the prostate
On the TRUS, prostate cancer appears as a less dense region than the darker, surrounding healthy prostate tissue. TRUS caused considerable excitement when it was first introduced, but it does have shortcomings that limit its use in screening. Studies have shown that it misses 24% to 30% of cancers that have the same density as the surrounding prostate tissue and that its ability to detect cancer is no better than DRE. However, TRUS remains a valuable tool to obtain biopsy samples.
