Abdominal and Small Parts Ultrasound Imaging: Prostate and Male Pelvis

Prostate and Male Pelvis Ultrasound Imaging Notes

Topics Covered

• Prostate Anatomy
• Prostate Physiology
• Laboratory Values
• US Scanning Techniques
• Prostate Pathology
• Male Pelvis (Penis) Anatomy and Pathology

Prostate Anatomy

Location and Structure

• Retroperitoneal gland: Located behind the peritoneum.
• Shape: Inverted pyramid, with its base superior and apex inferior.
• Position:
  • Lies between the bladder and urogenital diaphragm.
  • Anterior to the rectum.
  • Inferior to the bladder.
  • Surrounds the urethra.
  • Seminal vesicles are superior.
• Base: Superior portion, situated below the inferior margin of the urinary bladder.
• Apex: Inferior portion, situated superior to the urogenital diaphragm.
• Relationship with Urethra: The prostate surrounds the urethra, which passes through it. The ejaculatory ducts also empty into the urethra via the verumontanum.

Size and Volume

• Young Adult: Weighs approximately 20 \pm 6 g and measures on average 4 \text{ cm} \times 3 \text{ cm} \times 2 \text{ cm}.
• Volume Calculation: (Height \times Width \times Length) \times 0.52
• Normal Volume:
  • Young patients: 20 grams or less.
  • Older patients: Up to 40 grams.
  • Sonographically: Normal volume is less than 30 mL.

Lobes

Historically described as five lobes:

• Anterior
• Posterior
• Middle
• Lateral (2)

Zones

• Peripheral Zone (PZ):
  • Location: Posterior and lateral to the distal prostatic urethra, apical region of the prostate.
  • Size: Largest zone, approximately 70\% of the gland.
  • Pathology: Location of most prostate cancer (70\% of carcinomas).
  • Sonographic Appearance: Normal PZ tissue has a homogeneous, isoechoic echotexture.
• Transition Zone (TZ):
  • Location: On both sides of the proximal urethra, consists of two small lobules lateral to the proximal urethral segment.
  • Size: Smallest zone, accounts for about 5\% of prostate glandular tissue in younger men.
  • Pathology: Site of origin for Benign Prostatic Hyperplasia (BPH) (95\% of BPH originates here). May account for a much greater percentage of glandular tissue as men age. Approximately 20\% of carcinomas occur in this area.
  • Sonographic Appearance: Becomes more hyperechoic and visible with BPH.
• Central Zone (CZ):
  • Location: Extends from the base to the verumontanum, located at the base of the prostate. Situated between the peripheral and transition zones.
  • Relationship: Surrounds the ejaculatory ducts, which course through this region to join the urethra.
  • Size: Accounts for about 20\% of glandular tissue.
  • Pathology: Only about 5\% of prostate carcinomas arise in the central zone.
  • Sonographic Appearance: Echogenicity of the central zone is normally greater than that of the peripheral zone.
• Anterior Fibromuscular Stroma (AFS):
  • Previously called the anterior zone.
  • Structure: Thick sheath covering the entire anterior prostate surface, equating to up to 1/3 the size of the gland.
  • Composition: Made of smooth muscle and fibrous tissues.
  • Pathology: Contains NO glandular tissue, therefore not affected by cancer, inflammation, or BPH.
• Periurethral Glandular Zone: Glandular tissues that line the proximal prostatic urethra.

Related Structures

• Ejaculatory Ducts: Each vas deferens empties spermatic fluid into an ejaculatory duct of the ipsilateral seminal vesicle. The right and left ejaculatory ducts pass through the central zone and empty into the urethra.
• Verumontanum: A longitudinal ridge within the urethra that holds the openings from the ejaculatory ducts.

Seminal Vesicles

• Anatomy: Paired glands, lie obliquely and superior to the prostate, posterior lateral to the bladder.
• Function:
  • Reservoirs for seminal fluid and store sperm.
  • Secrete fructose to provide an energy source for sperm.
  • Secrete alkaline fluid to enhance sperm mobility.
  • Secretions mix with prostatic fluid to form semen during ejaculation.
• Sonographic Appearance:
  • Empty: Curvilinear, hypoechoic structures.
  • Full: Large, ovoid-shaped cystic structures, often containing low-level echoes within anechoic fluid.

Prostate Blood Supply and Drainage

• Arterial Supply: Internal iliac artery \to inferior vesicular arteries \to small perforating arteries that follow nerve branches for erection to form neurovascular bundles.
• Venous Drainage: Anterior plexus of Santorini merges with the dorsal penile vein to drain venous blood into the internal iliac vein.

Prostate Physiology

• Seminal Fluid Production: Contributes to seminal fluid by secreting an alkaline fluid (7.5 pH).
• Prostate Specific Antigen (PSA) Production: Acinar cells produce PSA, which is measured to assess prostate health.
  • Normal levels: Usually range from 0 ng/ml to 4 ng/ml.
  • Suspicious levels: 4-10 ng/ml is suspicious for malignancy.
  • Highly suspicious levels: >10 ng/ml usually related to malignancy.
  • Factors affecting PSA: Varies with patient age, gland volume, BPH, or malignancy.
  • Significance: Cancer elevates PSA much more significantly than BPH, but not all prostate cancers cause an elevated PSA level.

Laboratory Values

• Prostate Specific Antigen (PSA):
  • Elevated with: Prostate cancer, prostatitis, BPH, surgical manipulation.
  • Clinical example: A PSA of 6.0 is more worrisome in a 30-gram prostate than in a 150-gram prostate due to its concentration relative to gland size.
• Prostatic Acid Phosphatase (PAP): Elevated with prostate cancer.

Indications for US Prostate Exam

• Elevated PSA
• Urinary frequency
• Nocturia (waking at night to urinate)
• Poor urinary stream
• Enlarged prostate on digital rectal examination (DRE)
• Pain in back, thighs, or pelvis
• Pus or blood in urine or semen

Ultrasound Scanning Techniques

General Considerations

• Sonographic Appearance: Mid gray, medium-level echoes, homogeneous echotexture. Contours should be smooth, well-defined borders, symmetrical.
  • Seminal vesicles: Often appear as a