Transrectal ultrasonography (TRUS), shown in
the images below, plays a central role in the contemporary diagnosis of
prostate cancer because it enables accurate, image-guided biopsy of the gland.
Patients are usually referred for TRUS because an abnormality is found during
DRE or because the serum PSA level is elevated.
Axial transrectal ultrasonographic (TRUS) scan
shows extensive hypoechoic area (arrows) in the right peripheral zone. Biopsy
revealed prostatic adenocarcinoma.
Axial transrectal ultrasonographic (TRUS) scan
shows a hypoechoic area in left peripheral zone and a small hypoechoic area in
right peripheral zone (arrows). Biopsy revealed an adenocarcinoma (Gleason
grade 6).
Axial transrectal sonogram in a patient with
normal results during digital rectal examination and a prostate-specific
antigen (PSA) level of 9ng/mL. Image shows extensive bilateral, but
predominantly left-sided, hypoechoic areas in the peripheral zone (arrows).
Biopsy confirmed a Gleason grade 8 prostate cancer. Minor capsular irregularity
is present on the left; this is consistent with a T3 tumor.
Axial transrectal ultrasonographic (TRUS) power
Doppler scan in the same patient as in previous image. The patient had normal
results with digital rectal examination and a prostate-specific antigen (PSA)
level of 9ng/mL. A generalized increase in vascularity was noted in the
posterior aspect of the prostate (arrows). However, this finding is not
specific to the hypoechoic area in the left peripheral zone, illustrating the
difficulty of using Doppler techniques in the assessment of prostate cancer.
Axial transrectal ultrasonographic (TRUS) scan
in a patient with clinical benign prostatic hyperplasia (BPH) and a serum
prostate-specific antigen (PSA) level of 11ng/mL. Enlargement of the transition
zone is present, but no focal abnormality is observed in the peripheral zone.
Systematic, 6-core biopsy revealed adenocarcinoma from both lobes of the
prostate (ie, this is an isoechoic tumor in the peripheral zone of both
prostatic lobes).
TRUS is widely available, well tolerated by
patients, and relatively inexpensive. It currently offers the best opportunity
to demonstrate a prostate cancer, but because many prostatic tumors are both
isoechoic and multifocal, TRUS has major limitations in fully demonstrating
prostate cancers. Furthermore, TRUS has a low specificity because many
pathologic conditions may appear as similarly hypoechoic areas in the PZ of the
prostate. For this reason, diagnostic assessment of cancer in the prostate must
be made by means of histologic interpretation of biopsy samples. TRUS provides
the opportunity for accurate and comprehensive biopsy of the prostate gland
while providing an imaging examination.
Many pathologic processes can
appear as a hypoechoic area in the PZ of the prostate or as a hypervascular
area on color or power Doppler sonograms. The differential diagnoses of a
hypoechoic area in the PZ include prostatitis, tuberculous prostatitis, granulomatous
prostatitis, PIN, and prostatic atrophy and infarction. These are accurately
differentiated only by using biopsy of the focal ultrasonographic abnormality.
Furthermore, because many prostate cancers are isoechoic, these can be
identified only by using systematic biopsy techniques.
Imaging findings
With TRUS, the prostate is shown
to be divided into an outer gland (PZ and CZ) and an inner gland (TZ).
Calcification in the corpora amylacea in the surgical capsule between the outer
and inner parts of the prostate is common. Particular attention should be paid
to the PZ in prostate cancer diagnosis. The most frequently noted abnormality
caused by prostate cancer is a hypoechoic area in the PZ. Rarely, cancer may
appear as a hyperechoic area.
Prostate cancer and prostatitis
each may have increased vascularity, as shown on color and power Doppler
sonograms. This focal alteration in the prostatic vasculature is most commonly
found in hypoechoic areas in the PZ, as depicted on gray-scale images. No
cancer-specific flow pattern has been identified, and some cancers that are
demonstrated clearly on gray-scale Doppler imaging show no focal
hypervascularity.
Lymphoma of the prostate tends to
present in younger men, and large hypoechoic masses in the TZ and PZ have been
reported.
Prostate cancers frequently
demonstrate isoechoic findings. This observation is the basis for the
systematic biopsy approach in which multiple cores are taken from both lobes in
a standardized manner. Color and power Doppler study results have been
disappointing, and they have not been significantly helpful in detecting
cancers that are isoechoic on gray-scale examination.
Few reports in the published
literature describe the detailed sonographic appearances of the rarer
histologic variants of prostate cancer. In comedocarcinoma—the most malignant
form of prostate cancer—stippled, multiple, small, hyperechoic foci within the
hypoechoic area of the cancer have been reported. In one study, multiple small
cysts in the prostate were identified in 2 patients with adenoid cystic
carcinoma of the prostate.
Staging
TRUS may be used for local
staging of prostate cancer because it can demonstrate bulges of the prostate
capsular outline or overt extracapsular extension. TRUS findings have been
found to be inaccurate in the staging of localized prostate cancer, but PZ
tumors longer than 2.3cm that contact the fibromuscular rim surrounding the
prostate may be associated with extracapsular invasion.
TRUS-guided biopsy
The original systematic approach
to biopsy included the acquisition of 6 cores, with 1 core taken bilaterally
from each of the prostate lobes at the base, mid-gland, and apex in a
parasagittal plane (ie, a "sextant" biopsy). Current practice is to
obtain an increased number of cores (ie, lateral PZ cores, midgland cores, or
TZ cores) in addition to the standard 6 cores. A 10-core biopsy that
incorporates the traditional 6 parasagittal samples plus 2 lateral samples from
the right and left prostatic lobes is now a standard technique for systematic
biopsy.
Systematic biopsy may be
supplemented with cores obtained through hypoechoic PZ lesions. Focal areas of
hypervascularity in the PZ of the isoechoic prostate, as shown on color Doppler
examination, may also be targeted.
Opinions differ regarding whether
TZ cores should be routinely obtained during an initial biopsy procedure or
whether the samples may be obtained during repeat biopsy in a patient with an
elevated PSA level after the initial systematic biopsy results are negative for
malignancy.
Most TZ cancers are found by
analyzing systematic biopsy cores specifically obtained from the TZ. Little
attention has been paid to assessing hypoechoic areas in the TZ, because of the
lower frequency of cancer in the TZ and the perceived lower potential for
metastatic spread of primarily TZ cancer. No specific studies in the literature
report the biopsy results in focal TZ hypoechoic areas or in areas of specific
focal alterations of TZ vascularity, as identified by use of color or power
Doppler imaging.
Some authors describe a
saturation biopsy approach in which as many as 40 cores are obtained under general
anesthesia or
sedation. The precise biopsy approach must be individually tailored on the
basis of the patient's clinical features (eg, DRE and PSA levels).
Future perspectives
Currently, research studies are
under way to investigate whether ultrasonographic contrast agents have a role
in the identification of cancer in the prostate and whether, by demonstrating
tumor vascularity, they have a role in establishing prognosis of a patient with
biopsy-detected prostate cancer.
However, the use of
ultrasonographic contrast agents increases the time and cost of
ultrasonography-guided prostate biopsy procedures. No marked improvement has
been found in the accuracy of prostate cancer diagnosis with contrast agents.
These agents remain experimental, and they have not been adopted into standard
uroradiologic practice.
Nonetheless, the impact of
ultrasonographic contrast agents on radiologic practice could be considerable
if future research proves that they enable the quantitative preoperative
assessment of microvascular density or that they provide prognostic information
in an individual patient.
Research studies are also being
conducted to assess the value of elastography in the diagnosis of prostate
cancer; however, the role of this technique is still unclear.
In other research, Onik et al
found that 3-D prostate mapping biopsy (3-D–PMB; carried out transperineally
using a brachytherapy grid under TRUS guidance) can safely and accurately stage
prostate cancer patients. The investigators compared 3-D–PMB with traditional
TRUS biopsy in 180 patients with unilateral prostate cancer on TRUS biopsy. A
median of 50 cores were obtained with 3-D–PMB. In 110 patients (61.1%),
biopsies were positive bilaterally, and in 41 patients (22.7%), Gleason scores
were increased to 7 or higher.
