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Overview
Transrectal ultrasound (TRUS) is a 5- to 15-minute outpatient
procedure that 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 often 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 many tumors that cannot be felt by a DRE. In addition,
TRUS is used to estimate the weight 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.
Isoechoic areas, which represent normal tissue, bounce back, or
echo, the same amount sound waves as they received.
Hypoechoic areas send back significantly fewer echoes than they
received, and often indicate the presence of cancer.
Hyperechoic areas send back significantly more echoes than they
received, and often indicate the presence of prostatic
calcifications, or tiny stones, in the prostate. The stones are
usually harmless unless they become infected.
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 weight 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 weight of the prostate. PSA
levels exceeding 15 percent of the weight of the prostate are
more likely to indicate the presence of prostate cancer – and
the need for a biopsy. |
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