Diagnostic ultrasound ( PDFDrive )

CHAPTER 10 The Prostate and Transrectal Ultrasound 387
trends emphasize high central frequency (8-10 MHz) and broad
bandwidth. his increases spatial resolution but may decrease
lesion conspicuity. Probes with a center frequency of about 5 MHz
appear to provide a good balance between resolution and tissue/
cancer contrast. 23
Probes should be covered with sheaths or condoms during
the examination and sterilized between patients, following
manufacturers’ recommendations. Linear probes help with
transperineal techniques. 24
In general, rectal cleansing is done before the scan. A selfadministered
rectal enema is preferred, but laxatives can be used.
Some believe enemas decrease infectious complications of
biopsy. 25,26 A digital rectal examination before probe insertion
is performed to ensure that there are no rectal abnormalities to
interfere with safe probe insertion and to correlate images with
palpable abnormalities. he patient usually lies in a let lateral
decubitus position for the scan. Some examiners prefer a
lithotomy position, particularly if the examination is done in
conjunction with other urologic procedures or transperineal
interventions. With use of adequate lubrication, the probe is
gently inserted into the rectum. To decrease discomfort, viscous
lidocaine (Xylocaine) gel can be used as the lubricant in patients
with tight sphincters or anal pathology such as issures or inlamed
hemorrhoids.
A systematic approach works best for examination and helps
ensure that the whole gland is assessed. Typically the prostate
is scanned and appropriate images are taken, irst in gray scale
starting in the transverse plane, from the SVs and proceeding
to the apex, and then in the sagittal plane, from right to let lobe.
Subsequently the scan is repeated with Doppler low ultrasound
imaging in the transverse plane to evaluate vascularity and
vascular symmetry.
Measurements are taken as follows: maximal transverse width
(W; right to let), anteroposterior plane (AP; anterior midline
to rectal surface), length (L; maximal head to foot). Prostate
volume is usually calculated with the “oblate spheroid” formula:
volume = 0.5236 × (W × AP × L). Volume measurement is only
moderately repeatable to within 10%. Prostate volume can be
converted to prostate weight because the speciic gravity of
prostate tissue is about 1; thus 1 cc (mL) is equivalent
to 1 g.
Color or power Doppler ultrasound is used routinely when
searching for cancer. Vessel density is more easily evaluated with
power Doppler, which portrays color more evenly and is three
to ive times more sensitive than the color Doppler. Cancer
detection is increased by about 5% to 10% with use of power
Doppler, and vascular lesions have a slightly higher Gleason
score (5.9% vs. 6.9%). 27,28 Overall it is still felt that although
vascular density as shown by Doppler increases cancer detection,
its absence is not sensitive enough to avoid systematic biopsy.
Increased vascularity is not speciic and can be seen with
hypertrophy or inlammation, as well as cancer. 27,28 Spectral
Doppler indices (such as resistive index [RI], pulsatility index
[PI], and peak systolic velocity) vary with patient age and cannot
diferentiate between cancer and benign prostate conditions. 29
A pitfall of Doppler ultrasound is the normal, high vascular
density seen capping the base of the let and right lobes, which
should not be mistaken for enhanced vascularity seen
with tumors.
BENIGN CONDITIONS
Normal Variants
Benign ductal ectasia is seen in older men who develop atrophy
and dilation of peripheral prostatic ducts and has no clinical
signiicance. he ducts appear as single or grouped, 1- to
2-mm-diameter tubular structures in the peripheral zone radiating
from the capsule toward the urethra. Clusters of these can
form hypoechoic areas that could be mistaken as prostate cancer
(Fig. 10.7).
Prostatic calciications and corpora amylacea are normal
indings visible as bright echogenic foci or clumps consisting
of proteinaceous debris in dilated prostatic ducts, most oten
in periurethral glands and along the surgical capsule. When
densely clustered they can attenuate sound and block anterior
visibility, and on Doppler they create a prominent “twinkle”
artifact (see Fig. 10.7D). Subclinical infections, inlammation,
and atrophy may contribute to their formation. Corpora amylacea
have no clinical signiicance and are not usually palpable even if
dense or clumped. Peripheral zone calciications should not be
accepted as a cause for palpable irmness or nodules. Patients
with palpable abnormality need further evaluation, frequently
with biopsy.
Benign Prostatic Hyperplasia
Prostate enlargement with benign prostatic hypertrophy (BPH)
is a common cause of lower urinary tract symptoms (LUTS)
in older men and afects about 50% of men older than 60 years
and over 90% older than 70. he cause of BPH is unclear but is
probably related to hormonal changes with aging and results
in hypertrophy and hyperplasia of the ibrous, muscular,
and glandular elements, primarily afecting the transition and
periurethral zones. 1,19
Lower urinary tract symptoms, also called prostatism and
bladder outlet obstruction, can relate to increases in prostate
size and muscular tone, both causing urethral constriction.
Symptoms include frequency, nocturia, weak stream, hesitancy,
intermittence, incomplete emptying, and urgency and are quantiied
using the American Urological Association (AUA) symptom
index. 19,30 Many men have a misguided concern about prostate
size. he issue is urinary obstruction, not prostate size. Prostate
size correlates poorly with urinary obstruction. Urinary dysfunction
is multifactorial and can also arise from abnormalities of
the central nervous system, spine, bladder, prostate, and urethra.
Patients with urinary dysfunction need evaluation of all these
systems, not just the prostate. Ultrasound investigation of the
patient with symptoms of prostatism is best done transvesically
to assess prostate size, identify median lobe enlargement, and
evaluate bladder volume and postvoid residual, bladder wall
character, trabeculation, diverticula, tumors, and calculi, and
the kidneys and ureters should be evaluated for hydronephrosis
and masses. TRUS plays only a small role but helps if there is a
clinical concern for prostate cancer (BPH is one cause for PSA