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The Prostate Edited by

Dr.S.M.Nazmul Islam

The prostate is walnut/chestnut sized fibromuscular & glandular organ that is shaped like an inverted pyramid and lies posterior to the bladder. It is the largest accessory gland of the male reproductive system. The urethra passes through the centre of the prostate before traversing to the penis to end at the external urinary orifice. The prostate secrets a thin, milk-colored fluid that constitutes about 30% of the total seminal fluid volume. This fraction of the ejaculate helps to activate the sperm and maintain their mobility.

Prostate Anatomy

The weight of the gland in a young man is approximately 20 g. From age 50, the doubling time of prostate weight is approximately 10 years. Prostates weighing more than 40 g are generally considered enlarged in older men -Rumack Benign prostatic Hypertrophy (BPH) is normally graded as follows depending on volume / weight of the prostate.

I. Normal less than 30 cc. II. Grade I BPH = 30 – 50 cc / gm,

III. Grade III BPH = 50 – 70 cc / gm, IV. Grade III BPH = > 70 cc / gm.

A volume is taken by measuring height x length in the sagittal plane and x width in the axial plane and multiply by 0.52. Look for changes in the contours and echogenicity in each zone.

Scanning Technique: 1. Trans abdominal: a) Transverse/coronal & Sagittal/Longitudinal (Full urinary bladder) 2. Transrectal a) Coronal, Longitudinal and Axial (Empty Rectum with minimal urine)

Common Pathology of Prostate: Cysts: Prostate cysts have been grouped into six categories: (1) parenchymal cysts, (2) isolated medial cysts (utricle and müllerian), (3) ejaculatory duct cysts, (4) abscesses, (5) cystic tumors, and (6) cysts related to parasitic disease (schistosomiasis, hydatid disease). The most common cysts are parenchymal degenerative cysts in hyperplastic nodules in the transition zone. These have no clinical significance but on occasion can become large enough to contribute to urinary or ejaculatory obstruction. Benign Prostatic Hyperplasia (BPH): Usually the size (weight) is above normal, mostly occurs in central zone with possible median lobe protrusion into bladder and transitional zone. Isolated median lobe protrusion can be found even without prostate enlargement. Prostate Carcinoma: Hypoechoic areas & asymmetry. Mostly occurs in peripheral zone. Ca prostate can be present even without prostatic enlargement – correlation with PSA is essential for suspect. (hypoechoic nodule with marked vascularity)

Prostatitis: Acute- Hypoechoic or anechoic mass within the prostate that may look similar to a cyst, with thick walls and Septations. Chronic-Heterogeneous / focal masses. (hypoechoic prostate with gross augmentation of vascularity)

Enlarged seminal vesicles. Stones in the seminal vesicles, Prostate or ejaculatory ducts.

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Ultrasound of the Prostate - Protocol

Role of Ultrasound

BACKGROUND Visualization of the Prostate using the TRUS (Transrectal Ultrasound) technique has improved the diagnostic ability of the sonologist. It plays an important role in most prostatic diseases. It is necessary for all prostate biopsies. If the PSA is elevated or increasing rapidly or there is an abnormal prostate examination then a transrectal ultrasound and prostate biopsy may be indicated to obtain tissue to make the diagnosis of prostate cancer. Transabdominal Ultrasound can assess the volume of the prostate but is not reliable to diagnose carcinoma. In the early 1980s, transrectal ultrasound (TRUS) of the prostate was thought to be the pivotal imaging test of the prostate for benign and malignant conditions (e.g., benign hyperplasia, obstructive infertility) and for cancer evaluation, including screening, diagnosis, biopsy, staging, and monitoring of response to therapy. With experience and development of new techniques such as magnetic resonance imaging (MRI), the strengths and limitations of TRUS and other prostate imaging modalities have become better defined. Most patients currently are referred for TRUS for examination related to prostate cancer evaluation, biopsy, and guidance of therapeutic procedures. TRUS was initially considered a primary screening test for prostate cancer. This role has now been replaced by prostate-specific antigen (PSA) and digital rectal examination (DRE). Occasional patient referrals relate to infertility and prostatitis. TRUS guidance can also be used to biopsy any accessible lesion in the pelvis in both men and women.

Limitations Some patients are not able to cope with the probe inside their rectum for the duration of the scan (especially for a biopsy) during a TRUS. If patients are unable to fill their bladder with at least 60 mls of fluid then an accurate volume cannot be measured using a transabdominal approach.

Equipment Selection An endorectal, high frequency probe is used. It must have colour and Doppler capabilities. 3D scanning and contrast agents such as microbubbles will improve the assessment of vascularity. If scanning transabdominally a 3.5MHz to 6MHz curved linear array probe, depending on the size of the patient should be used.

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Patient position TRUS The rectum should be emptied prior to the scan. A small amount of fluid in the bladder is needed to identify it while scanning. The patient lies in a lateral decubitus position. Ensure that a generous amount of gel is put into the sphincter before inserting the probe. Transabdominal technique needs the patient supine.

Scanning Technique Full urinary bladder is required for prostate on abdominal scanning in supine position.

Now-a-days Trans rectal transducer (TRUS) is preferred for prostate scanning. But abdominal scanning has still a place.

Transverse& longitudinal scans both are performed.

Prostate lies deep caudally. So the transducer should be angled caudally on midline for proper visualization. Perpendicular to table top or slight cephaloid angulation will cause non-visualization of capsule.

On longitudinal scan, prostate appears posterior to urinary bladder. Seminal vesicles lie lateral to prostate.

On transverse scan, prostate appears indenting posterior part of bladder.

TRUS TECHNIQUE It is ideal to have a small amount of urine in the bladder. Ask the patient to try and relax and "bear down" to open the sphincter as the transducer is inserted slowly. Ensure the transducer has a latex free dedicated probe cover with plenty of gel. The highest frequency sector probe 7-12MHz should be used. The scanning begins in the axial plane. The seminal vesicles are examined initially. As the probe is angled caudally the base of the prostate is seen. Once the prostate is examined in its entirety in this plane the probe is turned 90 degrees in a sagittal plane. The probe is angled from one side across to the other.

A volume is taken by measuring height x length in the sagittal plane and x width in the axial plane

and multiply by 0.52. Look for changes in the contours and echogenicity in each zone.

TRANSABDOMINAL TECHNIQUE The patient lies supine. The patient should have a half full bladder. 500 mls of water 1 hr before the scan if possible is recommended. The probe is angled approximately 30 degrees caudal using the bladder as a window. Slight compression to ensure the inferior portion of the prostate is not obscured by the shadow artifact from the base of the bladder.

Common Pathology Cysts

Benign Prostatic Hyperplasia (BPH) Prostate Carcinoma

Prostatitis Enlarged seminal vesicles

Stones in the seminal vesicles, Prostate or ejaculatory ducts

Normal Anatomy & Sonographic findings of prostate The prostate is fibromuscular & glandular organ that is shaped like an inverted pyramid and lies posterior to the bladder. It is the largest accessory gland of the male reproductive system. The urethra passes through the centre of the prostate before traversing to the penis to end at the external urinary orifice. The prostate secrets a thin, milk-colored fluid that constitutes about 30% of the total seminal fluid volume. This fraction of the ejaculate helps to activate the sperm and maintain their mobility. The prostate gland is found inferior to the seminal vesicles between the bladder the bladder and rectum. The ejaculatory ducts descent inferiorly through the posterior portion of the gland and open into the prostatic urethra.

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SONOGRAPHIC APPEARANCE Various scanning orientations have been proposed; the most common matches that for transabdominal sonography and other cross sectional imaging modalities (see Fig. 10-1). The images are displayed as though one stands at the feet of a supine patient and looks headward. The rectum is displayed at the bottom of the screen, with the ultrasound beam emanating from within the rectum. On transverse imaging, the anterior abdominal wall is at the top of the screen, with the right side of the patient on the left side of the image (see Fig. 10-2). In a sagittal plane, the anterior abdominal wall is again located at the top of the screen, and the head of the patient is on the left side of the image (see Fig. 10-3).

Prostate “Capsule” On transverse and sagittal imaging, the border of the prostate with the periprostatic fat appears sharply defined except at the posterolateral margins, where the neurovascular bundle enters the prostate and makes the margin look ragged (see Fig. 10-2, C). Histologically, the prostate does not have a true membranous capsule but rather just condensed connective tissue through which the vessels and nerves course. In addition to the absence of a well-defined capsule, the presence of prominent but normal vessels in the periprostatic soft tissues posterolaterally may make assessment of “capsular” integrity difficult in patients with prostate cancer.

Role of Transrectal Ultrasound Unlike originally thought, TRUS has not been pivotal in men suspected to have cancer (e.g., screening, detection, biopsy guidance, staging, therapy guidance, monitoring response to treatment). Experience has shown that all imaging modalities, including TRUS, CT, and MRI, have strengths and limitations in investigating patients.

Elastography - Elastography is being evaluated. Elastography creates a color-coded map of tissue

“stiffness” (elastic modulus). Some prostate tumors have increased cell density, leading to change of tissue elasticity and stiffness, which may be amenable to detection by “strain imaging.” When the prostate is gently deformed by hand-controlled probe pressure, areas of different density/stiffness in the prostate are portrayed by different colors.

Normal Prostate Anatomy

Lobes

The "Lobe" classification is more often used in anatomy.

Anterior lobe (or isthmus Roughly corresponds to part of transitional zone

Posterior lobe Roughly corresponds to peripheral zone

Lateral lobes Spans all zones

Median lobe (or middle lobe) Roughly corresponds to part of central zone

Zones The "zone" classification is more often used in pathology. The idea of "zones" was first proposed by McNeal in 1968. McNeal found that the relatively homogeneous cut surface of an adult prostate in no way resembled "lobes" and thus led to the description of "zones". The prostate gland has four distinct glandular regions, two of which arise from different segments of the prostatic urethra:

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Prostate Zonal Anatomy:

Name Function of the gland Description Peripheral zone (PZ)

Up to 70% in young men

The sub-capsular portion of the posterior aspect of the prostate gland that surrounds the distal urethra. It is from this portion of the gland that 70–80% of prostatic cancers originate.

Central zone (CZ)

Approximately 25% normally

This zone surrounds the ejaculatory ducts. The central zone accounts for roughly 2.5% of prostate cancers although these cancers tend to be more aggressive and more likely to invade the seminal vesicles.

Transition zone (TZ)

5% at puberty

10–20% of prostate cancers originate in this zone. The transition zone surrounds the proximal urethra and is the region of the prostate gland that grows throughout life and is responsible for the disease of benign prostatic enlargement.

Anterior fibro-muscular zone (or stroma)

Approximately 5% This zone is usually devoid of glandular components, and composed only, as its name suggests, of muscle and fibrous tissue.

Prostatic Size & Volume Benign prostatic Hypertrophy (BPH) is normally graded as follows depending on volume / weight of the prostate.

I. Normal less than 30 cc. II. Grade I BPH = 30 – 50 cc / gm,

III. Grade III BPH = 50 – 70 cc / gm, IV. Grade III BPH = > 70 cc / gm.

V. Prostate has a capsule. So prostate gives a regular outline normally and in BPH. But in prostate malignancy this normal regular smooth outline is lost.

It is about the size of a chestnut /walnut and

somewhat conical in shape. Its weight is within 30 gm or cc.

Measurements Transverse @ the base (T) : about 4 cm Anteroposterior (A-P) : about 2 cm & Vertical diameter/Length (L): about 3 cm. Reference: Diagnostic USG – Gupta.

Volume formula: (T) Transverse x A-P

(Anterior - Posterior) x L (Length) x 0.5 in cm = CC / gm.

In a 20 years man, prostate is considered normal → up to 20 gm

The weight of the gland in a young man is approximately 20 g. From age 50, the doubling time of prostate weight is approximately 10 years. Prostates weighing more than 40 g are generally considered enlarged in older men -Rumack

Fig.19- 1: Prostate Anatomy (Axial View) Fig. 19-2: Prostate Anatomy (Longitudinal View)

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A, Coronal section at mid-

prostate level.

B, Sagittal midline section.

C, Parasagittal section.

D, Axial section through base.

E, Axial section through apex

=Transition zone =Peri urethral glandular area

=Verumontanum =Seminal vesicle

=Central zone =Ejaculatory duct

=Fibromuscular stroma = Central Zone

FIGURE 10-1. Diagram of prostate zonal anatomy. This is the anatomy in a young man because the transition zone (white areas) is small. The transition zone will undergo marked enlargement in older men with benign prostatic hyperplasia (Ref. RUMACK)

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Fig. 19-3: Section of Longitudinal Scan Fig. 19-4: LT: Transverse/Axial View

FIGURE 10-2. Axial sonograms of prostate. A, Transverse image above base shows the seminal vesicles (SV) and vas deferens (V); B, bladder. B, Axial scan at mid gland level. Note the normal hypoechoic muscular internal urethral sphincter (horizontal arrows) and the ejaculatory ducts (vertical arrow). C, Axial scan at lower third of prostate shows hypoechoic urethra (U). Most of the visible gland at this level is peripheral zone. Note the irregular outline at the posterolateral aspects (arrows), resulting from the entrance of the neurovascular bundles. D, Axial scan just below apex of prostate shows cross section of distal urethra (U). Pelvic sling muscles are visible (arrows). -Ref. RUMACK.

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FIGURE 10-3. Sagittal views of prostate. A, Midsagittal view shows internal urethral sphincter (white arrows), which contains the echogenic collapsed urethra (*). The ejaculatory ducts (E) course from the vas deferens (V) to the verumontanum (oblique arrow). B, Midsagittal view at base shows the vas deferens (V) and adjacent seminal vesicles (S) as they enter the prostate. C, Parasagittal view shows the lateral prostate, which is homogeneous and isoechoic and composed almost totally of peripheral zone tissue; SV, seminal vesicle. D, Parasagittal view above the prostate shows the normal seminal vesicles (SV) and vas deferens (V) in cross section above the prostate (P). Ref. RUMACK

NORMAL PROSTATE IMAGES - TRANSABDOMINAL & TRANSRECTAL APPROACH

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