Diagnostic ultrasound ( PDFDrive )

384 PART II Abdominal and Pelvic Sonography
he peripheral zone, the largest of the glandular zones, arises
from the urogenital sinus and in a young man before the onset
of benign prostatic hyperplasia (BPH) contains approximately
70% of the prostatic glandular tissue and is the site for about
70% of prostate cancers. 17,18 It is separated from the transition
zone and central zone by the surgical capsule, a hypoechoic
line that is rendered hyperechoic by the frequent accumulation
of corpora amylacea or calciications along it. Traditionally,
urologists at the time of suprapubic or transurethral prostate
resection believed that they dissected to this line, which demarked
hypertrophied periurethral glands from posterior lobe—hence
“surgical” capsule. he peripheral zone occupies the posterior,
lateral, and apical regions of the prostate, extending anteriorly
around the margins, like an egg cup holding the “egg” of the
central gland (Fig. 10.4A).
he young transition zone contains about 5% of the prostatic
glandular tissue. It is visible as two small glandular areas
positioned like saddlebags adjacent to the proximal urethral
sphincter, which is a muscular tube up to 2 cm in diameter.
It is the site of origin of most BPH and about 20% of prostate
cancers. 17,19
he central zone along with the seminal vesicles (SVs) arises
from the wolian ducts. It constitutes approximately 25% of the
glandular tissue and is wedged at the prostate base between the
peripheral and transition zones. he ducts of the vas deferens
(VD) and SVs enter the base of the prostate at the central zone,
where they are renamed the ejaculatory ducts and pass through
it en route to the verumontanum. he central zone is relatively
resistant to disease processes and is the site of only about 5% of
prostate cancer. 17-19
At the base of the prostate at the bladder neck is the thick,
muscular, continence-providing, internal urethral sphincter.
Its substantial homogeneous muscle content can make it appear
hypoechoic. It contains periurethral glands that oten contain
calciications. 12,13,19
Vascular and Neural Structures
he prostate is supplied by the prostaticovesical arteries, which
arise from the internal iliac arteries on each side and give rise
to the prostatic artery and inferior vesical artery. he prostatic
artery gives rise to the urethral and capsular arteries. he inferior
vesical artery supplies the bladder base, SVs, and ureter. he
urethral artery supplies about one-third of the prostate, and the
capsular branches supply the remainder. 20
On Doppler ultrasound the prostate is mildly to moderately
vascular. he neurovascular bundles are visible at the posterolateral
angles (Fig. 10.5). he capsular and urethral arteries are easily
seen, and branches to the inner gland and peripheral zone are
visible in a somewhat radial pattern with the periurethral vessels
as the axle. A dense cluster of vessels is oten seen capping the
base of the prostate, and care must be taken not to mistake these
for tumor vascularity. 20
Nerve supply to the prostate has been clariied. 15,21,22 Parasympathetic
supply is through the S2-S4 sacral roots, and
sympathetic supply is through the hypogastric nerve. hese
combine in the pelvic plexus just above and lateral to the prostate
and give rise to about 6 to 16 small branches that supply the
SVs, prostate, levator ani, and corpora cavernosa. he cavernosal
branches are responsible for erections. he nerves and blood
vessels travel together as the neurovascular bundle in the
Denonvilliers (rectoprostatic) fascia at the posterolateral aspect
of the prostate, where the vessels are visible with color low
Doppler ultrasound. hese nerves are vulnerable to injury during
surgery, radiotherapy, and other interventions and are avoided
at nerve-sparing prostatectomy to preserve potency. 15,21,22
SONOGRAPHIC APPEARANCE
Images are oriented using the standards for abdominal sonography
and other cross-sectional imaging modalities. he images are
displayed as though one were standing at the feet of a supine
patient and looking headward. he rectum is at the bottom of
the screen; the right prostate is on the let of the screen. On
sagittal views, the base (head end) is on the let side.
On axial ultrasound, above the prostatic base, the seminal
vesicles are paired, relatively hypoechoic, multiseptated structures
cephalad to the base of the prostate normally measuring about
1 cm diameter (see Fig. 10.2A). he adjacent vasa deferentia are
visible as uniform muscular tubes measuring about 6 mm in
diameter coursing from the internal inguinal ring to lie beside
the SVs and enter the midbase of the prostate, where they become
the ejaculatory ducts, which connect to the verumontanum
(seminal colliculus).
In the axial plane, the urethra between the bladder neck and
verumontanum and its surrounding smooth muscle, the internal
sphincter, can be a quite conspicuous hypoechoic structure
measuring 2 cm in diameter that can mimic the appearance of
a transurethral resection defect (see Figs. 10.2B and 10.3A). hose
unfamiliar with transrectal and pelvic ultrasound may mistake
the sphincter for hypoechoic tumor. he muscular sphincter
ends at the verumontanum, which forms a small bulge pointed
anteriorly, oten with a small, conspicuous calciication at its
apex, giving it an Eifel Tower appearance.
he inner transition zone is separated from the peripheral
zone by the usually hypoechoic surgical capsule (see Fig. 10.4A).
his line is less visible in young men but becomes conspicuous
as BPH enlarges the transition zone (see Figs. 10.2B and 10.4A).
he peripheral zone has a uniform, homogeneous texture and
is slightly more echogenic than the transition zone. Peripheral
zone echogenicity is deined as isoechoic and taken as the standard
for prostate echogenicity and other areas of the gland are compared
to its echogenicity. Laterally, the peripheral zone curves
anteriorly to enclose the transition zone. his upward curved
part was named the “anterior horns” by Babaian from Texas
because it resembled the horns of a steer. Prominent veins of
Batson venous plexus are visible in the periprostatic fat, sometimes
containing calciied shadowing phleboliths. 12
On midsagittal view the muscular internal urethral sphincter
extends from the bladder to the verumontanum, sometimes
surrounded by corpora amylacea in the periurethral glands (see
Fig. 10.3A). he anterior ibromuscular zone is an inconspicuous
area anterior to the internal sphincter. At the verumontanum
the distal urethra angles slightly anteriorly and ultimately exits
the apex of the prostate just before it enters the urogenital