The digital rectal examination (DRE) and the prostate-specific antigen (PSA) blood test are two important ways to detect changes in the prostate gland.
However, they cannot determine if the changes are due to prostate cancer or to a non-cancerous condition. In the event of a significantly elevated PSA test and/or abnormal DRE, a prostate needle biopsy -- the surgical removal of tissue for examination under a microscope -- must be performed in order to make a definitive diagnosis of prostate cancer. The biopsy is taken with the guidance of transrectal ultrasound.
Transrectal
ultrasound (TRUS) is a 5- to 15-minute outpatient
procedurethat uses sound waves to create a video image
of the prostate
gland. A small, lubricated
probe placed into the rectum releases sound waves, which
create
echoes as they enter the prostate. Prostate tumors sometimes
create echoes that are different from normal prostate tissue.
The
echoes that bounce back are sent to a computer that translates
the pattern of echoes into a picture of the prostate. While
the probe may be temporarily uncomfortable, TRUS is essentially
a painless procedure.
Although TRUS alone cannot detect every tumor, it has been
shown to detect some tumors that cannot be felt by a DRE.
In addition, TRUS is used to estimate the size of the prostate
gland, helping doctors get a better idea of
PSA density, which helps distinguish benign prostatic hyperplasia (BPH) from
prostate cancer. Finally, it plays a
vital role in a prostate needle biopsy, guiding the
needle to just the right part of the prostate
gland.
Preparation for TRUS
Prior to TRUS, the patient may be instructed to have an enema
to remove feces and gas from the rectum, which might impede
the progress of the rectal probe.
TRUS technique
The patient traditionally lies on his left side, which is
considered a more relaxing position as well as allowing for
easier insertion of the rectal probe. After the probe is inserted
into the rectum, the tester adjusts the console on the ultrasound
machine to a baseline for the echoes of normal prostate tissue,
which will serve as the standard by which other tissue will
be classified. Imaging is usually begun at the base of the
bladder, as the probe is rotated to provide a full picture
of the prostate.
Images
The rectal probe sends sound waves to the prostate gland;
normal and abnormal tissue bounce back different kinds of
echoes that are relayed to the computer, which translates
their pattern into a video picture of the prostate.
PSA
Density (PSAD)
Most men in the age group for prostate cancer usually have
some BPH as well, which can elevate PSA levels and make prostate
cancer diagnosis more difficult. PSA density -- the blood
PSA level divided by the size of the prostate, as determined
by TRUS -- can help distinguish between BPH and prostate
cancer.
Basically, with BPH, the PSA level should not be more than
15 percent of the size of the prostate. PSA levels exceeding
15 percent of the size of the prostate are more likely
to
indicate the presence of prostate cancer -- and the need
for a biopsy.
The Prostate Cancer pages of this Web site are part of the Comprehensive Prostate Cancer Awareness Program (CPCAP), a major regional effort to reduce the rates of death and illness caused by prostate cancer in southwestern Pennsylvania. Funding for CPCAP is provided by a grant from the Commonwealth of Pennsylvania.
