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Doppler imaging of the
prostate
10
Fred T. Lee, Jr
INDICATIONS
The most important use of colour Doppler
imaging of the prostate remains as an aid in
cancer detection. This is particularly relevant in
patients in whom cancer is suspected based on
prostate specific antigen (PSA) elevation without
obvious tumour on grey-scale imaging. Other
uses for Doppler imaging are largely confined to
detection of prostatitis and inflammatory conditions. Controversy continues surrounding diagnosis and treatment of prostate cancer. This is
largely attributable to the wide range of biological behaviour found with this disease. Up to
30% of 80-year-old males will have histological
evidence of prostate cancer, yet most will die
from other causes. Unfortunately, a more aggressive subset remains an important cause of mortality
among men, with 30350 deaths expected in the
USA in 2005.1
ANATOMY
The prostate lies immediately anterior to the
rectum and inferior to the bladder. Prostatic
zonal anatomy has been extensively described by
McNeal et al.2 In summary, the prostate is
composed of three major zonal areas; the
peripheral zone, the central zone and the transition zone (Fig. 10.1). The peripheral zone is the
most posterior, and the central zone is a continuation of the peripheral zone cephalad. The
transition zone is the most central area of the
prostate, and surrounds the urethra as it courses
through the prostate.The anterior fibromuscular
stroma lines the prostate anteriorally.
Prostate vascular anatomy
The prostate is supplied from two arterial sources:
the prostatic arteries and the inferior vesical
arteries, both arising from the internal iliac
system. The prostatic arteries enter the prostate
from an anterolateral location on each side, and
give off capsular branches as well as urethral
branches. Capsular arteries course along the
lateral margin of the prostate, and give off
numerous perforating branches which penetrate
the capsule and supply approximately two-thirds
of the total glandular tissue. The areas of penetration into the capsule are commonly referred
to as the neurovascular bundles (Fig. 10.2). The
inferior vesical arteries run along the inferior
surface of the bladder and also provide urethral
branches. In addition to supplying the central
portion of the prostate, the inferior vesical
arteries also give off branches which supply the
bladder base, seminal vesicles and distal ureters
(Fig. 10.3).3,4 Both the capsular and urethral
branches can be visualised with colour Doppler
ultrasound. In the absence of inflammation,
neoplasm or hypertrophy the normal prostate
is expected to have low level periurethral and
pericapsular flow, with only a low level of flow in
the prostatic parenchyma.5
EQUIPMENT AND TECHNIQUE
Examination of the prostate by ultrasound
requires a high-frequency (5–7.5 MHz) end-fire
or biplane transrectal transducer. For the
purposes of this chapter, conventional colour
Doppler and power Doppler are considered
simultaneously. For most general applications,
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Doppler imaging of the prostate
10
∗
∗
Fig. 10.1 Axial ultrasound of the prostate in a
normal patient. Note peripheral zone (*) separated
from the more centrally oriented, periurethral,
transition zone by the surgical capsule (arrows).
Fig. 10.2 Axial image of the left neurovascular
bundle. Note left neurovascular bundle (arrow) with
perforating branches penetrating into the prostate
(arrowheads).
∗
246
Fig. 10.3 Sagittal image of the prostate at the level
of the seminal vesicle (*) demonstrates periurethral
flow (arrows) originating from the inferior vesicle
artery.
an end-fire transducer is favoured due to the
ease of switching between axial (coronal) and
longitudinal imaging planes, as well as the more
favourable angle for transrectal prostatic biopsies.
For specialised applications such as prostatic
volumetry and cryosurgery, a true biplane transducer is necessary.
No specific patient preparation is required
although some centres will give the patient a
pre-examination enema and have them empty
their bladder. The patient is generally placed in
the left lateral decubitus position, and the knees
brought up to the chest. A digital rectal examination is recommended prior to probe insertion
to rule out any obstructing pathology and also to
allow the examiner to evaluate the prostate by
digital examination. The probe is covered with
a condom into which coupling gel has been
placed, and the probe lubricated and gently
inserted into the rectal canal. Examination of the
prostate by grey-scale imaging is first performed,
and the length, width and height of the gland
measured. The prostatic volume is calculated
based on the formula for a prolate ellipsoid
(length × width × height × 0.523); this allows
correlation of the measured PSA with a predicted
PSA based on gland volume. Normal prostatic
tissue produces approximately 0.3 ng cc-1 of PSA,
whereas cancerous tissue produces approximately
3.0 ng cc-1 of tumour. Normal levels for polyclonal
assays are typically defined as <4.0 ng mL-1;
unfortunately, up to 20% of prostatic cancers
present in patients with ‘normal’ levels of PSA.
A ‘predicted’ PSA can be generated based on
the patient’s gland volume × 0.2 for polyclonal
assays (or gland volume × 0.1 for monoclonal
assays). A level of measured PSA that exceeds
predicted PSA increases the suspicion of cancer
and increases the positive predictive value of
prostatic biopsy.6
Most prostate cancers (70%) arise in the
peripheral zone, with a minority originating in
the central (10–15%) and transition zones
(10–15%). Because of this, it is very important
that the sonographer carefully examine the
peripheral zone for signs of tumour. Virtually all
prostate cancers will be hypoechoic in relation to
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Doppler imaging of the prostate
COLOUR DOPPLER OF PROSTATE
CANCER
Knowledge of the excess PSA for a particular
gland is most important from an ultrasound
standpoint when an obvious peripheral zone
tumour is not found in the face of an elevated
measured PSA. As previously mentioned,
transition zone tumours are difficult to visualise
by grey-scale criteria due to the in homogeneous
nature of normal transition zone tissue. Once
it is established that the patient is at high risk
for prostate cancer by PSA criteria, and no
peripheral zone cancer has been found, a careful
Fig. 10.4 Prostate cancer. Axial image of the prostate
at the mid-gland. Hypoechoic tumour (+) originates in
the left neurovascular bundle area.
Colour Doppler of prostate cancer
normal peripheral zone tissues (Fig. 10.4),
although a minority of cribriform carcinomas
can demonstrate punctate calcifications.Tumours
in the peripheral zone have ready access to sites
of anatomical weakness, including the neurovascular bundles, ejaculatory ducts and apex of the
gland. This results in more aggressive clinical
behaviour of peripheral zone tumours when
compared to other locations. Transition zone
tumours tend to behave in a clinically more
benign manner because they are distant from
sites of anatomical weakness, and thus need to
grow quite large before spreading outside of the
gland. The main problem with the diagnosis of
transition zone tumours is the heterogeneous
echotexture of the normal transition zone.
Because normal transition zone tissue can be
hypoechoic, hyperechoic or contain calcifications
or cysts, it is extremely difficult to diagnose subtle
changes in echogenicity that may be associated
with neoplasia.Therefore, colour Doppler can play
a crucial role in the diagnosis of transition zone
tumours by identifying areas of abnormal flow.
10
examination of the transition zone should be
undertaken. It is in the search for transition zone
tumours that colour Doppler ultrasound has
proven to be most useful. Prostate cancer is
generally hypervascular when compared to
normal prostatic tissue and this is manifested as
increased colour encoding at sensitive instrument settings (Fig. 10.5). These can be targeted
for biopsy with increased positive biopsy rates
compared to blinded sextant biopsies. It is
controversial as to whether targeted biopsies
using color Doppler alone can replace sextant
biopsies.7 Early work using contrast enhanced
color Doppler ultrasound demonstrates an
increased sensitivity for the detection of prostate
cancer,8, 9 but the exact type of contrast material,
imaging algorithm and time after injection has
not yet been standardised. Additionally, ultrasound contrast agents have not yet been approved
for use in the USA. Spectral Doppler plays a
limited role in the specific diagnosis of prostate
cancer. Tumours tend to have low resistance
(high diastolic) flow, although the exact role and
specificity of this finding has yet to be fully
elucidated.
Fig. 10.5 Transition zone prostate
cancer (biopsy proven). Axial (left)
and sagittal (right) images
demonstrate a hypervascular
tumour in the transition zone
(arrows).
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Doppler imaging of the prostate
10
The use of colour Doppler in the diagnosis of
peripheral zone tumours is more controversial.
Several authors have found increased colour
Doppler flow to have no significant correlation
with the presence or absence of tumour at
histology. In addition, there has been no colour
Doppler method consistently to discriminate
tumour from focal prostatitis in areas of increased
flow. Others have found biopsy of sites of
increased flow useful in the face of an increased
measured PSA (greater than predicted) and no
other obvious sites of tumour.10 This has been
found to be particularly useful in black males,
where the positive predictive value for biopsy of
a focal area of increased colour encoding has
been found to be twice that of white males (32.2%
vs 13.5% respectively).11 Most authors now feel
that colour Doppler is more of a complementary
test to grey-scale ultrasound, PSA and gland
volume rather than a single factor on which to
base biopsy decisions (Fig. 10.6).
COLOUR DOPPLER OF PROSTATIC
INFLAMMATORY DISEASE
Prostatitis is a difficult condition to diagnose
and treat.There are several aetiologies of prosta-
titis, ranging from bacterial to non-bacterial
causes. In the case of bacterial prostatitis, the
offending organism is usually Escherichia coli or
other urinary tract pathogens.
Grey-scale findings of acute prostatitis include
an hypoechoic rim around the prostate or periurethral areas, and low level echogenic areas
within the prostate.12 Colour Doppler is useful
in cases of diffuse bacterial prostatitis.The severity
of the inflammatory reaction is mirrored by
focal or diffuse increase in the colour signal in
the prostatic parenchyma.13 When focally
increased colour signals are seen in cases of
prostatitis, there is no reliable non-invasive
method to differentiate inflammation from
tumour.13 However, cases of grossly increased
flow spread diffusely throughout the gland should
be considered prostatitis in the appropriate clinical
setting (Fig. 10.7). When the inflammatory
process continues to suppuration, a prostatic
abscess can develop. On ultrasound, this is seen
as a cavity filled with low-level echoes from
debris (Fig. 10.8).14 Colour Doppler may detect
increased flow around the rim of the cavity,
although this finding is not necessary to make
the diagnosis. Cases of bacterial prostatitis are
treated by antibiotics, whereas prostatic abscess
a
Axial
b
248
Sagittal
Fig. 10.6 Peripheral zone
prostate cancer. (a) Axial and
sagittal grey-scale images
demonstrate a subtle hypoechoic
area in the left neurovascular
bundle (arrows). Biopsy through
this area was positive for
adenocarcinoma, Gleason score
6. (b) Axial and sagittal colour
Doppler images at corresponding
locations demonstrate increased
colour flow in areas involved by
tumour.
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Doppler imaging of the prostate
CONCLUSIONS
Fig. 10.7 Prostatitis. Colour Doppler image of
diffuse prostatitis demonstrates grossly increased
flow throughout the gland.
Conclusions
requires transrectal catheter or transurethral
drainage with unroofing of the abscess cavity.
10
Doppler ultrasound of the prostate contributes
significantly to the diagnostic value of sonography in the assessment of prostatic disease. Colour
and power Doppler identify areas of abnormal
blood flow, which can then be examined more
closely with grey-scale imaging, or biopsied under
ultrasound guidance.
Fig. 10.8 Prostatic abscess.
Markedly hypoechoic lesion with
subtle through transmission is
present in the peripheral zone of
this patient. Note lack of flow in
the central portion of this lesion,
a finding that would be very
unusual for prostate cancer.
Drainage confirmed the presence
of an abscess.
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