Prostate Anatomy and Function

Prostate

Prostate Embryology

  • The prostate develops from epithelial outgrowths from the prostatic segment of the urethra.

  • Outgrowth initiation starts at week 10 of embryonic development.

Prostate Location

  • Location:

    • Retroperitoneal gland.

    • Inferior to the urinary bladder.

    • Posterior to the symphysis pubis.

    • Anterior to the rectum.

Prostate Function

  • Function:

    • It is classified as an exocrine gland.

    • The prostate secretes an alkaline, milky substance constituting approximately 20% to 30% of semen.

    • The alkaline fluid aids in prolonging the lifespan of sperm in the acidic vaginal environment.

Prostate Anatomy

  • The prostate is approximately the size of a walnut.

  • Size Variation:

    • The size of the prostate varies with age, measuring roughly 4 x 2 x 3 cm.

    • Typically begins enlargement around the age of 40.

Prostate Shape

  • The prostate resembles an inverted rounded pyramid.

  • Base:

    • The superior aspect and the widest part, resting against the inferior wall of the urinary bladder.

  • Apex:

    • The inferior aspect, representing the narrowest part of the gland.

Prostate Zones

  • The prostate is divided into four zones:

    • Peripheral Zone (PZ):

      • Outermost zone, largest, consisting of about 70% of glandular tissue.

      • Most likely area for malignancy occurrence.

    • Central Zone (CZ):

      • Comprises about 25% of the prostate.

      • Surrounds the ejaculatory ducts; cancers in this zone are less common but tend to be more serious.

      • Cancer here can spread to the seminal vesicles.

    • Transitional Zone (TZ):

      • Smallest zone, surrounding the prostatic urethra.

      • Responsible for many symptoms associated with an enlarged prostate.

    • Anterior Fibromuscular Stroma (AFS):

      • Contains muscle and connective tissue (stroma).

      • No functional glandular tissues present.

Blood Supply to the Prostate

  • Arterial Supply:

    • Begins with the internal iliac artery, branching into the inferior vesical artery, which further divides into two segments that supply blood to the prostate:

      • Prostatic artery.

      • Capsular artery.

Venous Drainage of the Prostate

  • Multiple tiny veins in the prostate drain into the dorsal vein (which drains the penis) and eventually into the venous plexus, leading to the internal iliac vein.

The Male Urethra

  • In males, the urethra is responsible for:

    • Excreting fluid waste (urine).

    • Excreting seminal fluid.

Length of the Male Urethra

  • The male urethra is approximately 20 cm long, extending from the bladder to the tip of the penis.

  • For comparison, the female urethra is about 4 cm long, thus making females more susceptible to urinary tract infections (UTIs).

Sections of the Male Urethra

  • The male urethra is divided into three sections:

    • Prostatic Section:

      • Most proximal part, measuring about 2.5 cm in length.

      • Extends from the neck of the urinary bladder to the mid-portion of the prostate.

      • Accepts drainage from tiny ducts within the prostate and the ejaculatory ducts.

    • Membranous Section:

      • The shortest segment, measuring approximately 0.5 cm in length.

      • Extends from the inferior aspect of the prostate to the proximal aspect of the penis.

    • Spongy Section:

      • The longest section, measuring approximately 15 cm, extending the entire length of the penis to the external orifice.

Seminal Vesicles

  • Anatomy of Seminal Vesicles:

    • Paired tubular hypoechoic structures.

    • Located posteroinferior to the urinary bladder, measuring about 4–5 cm in length.

    • Produce fluid that mixes with sperm to form semen.

    • The fluid is rich in sugars, providing nourishment to the sperm.

Anatomy Related to Seminal Vesicles

  • Fluid from the seminal vesicles empties into the ejaculatory ducts, which are surrounded by the central zone of the prostate.

  • The ejaculatory ducts are formed from the union of the vas deferens (ductus deferens) and the seminal vesicle.

  • The junction between the ejaculatory duct and the prostatic urethra is known as the verumontanum.

  • The vas deferens is a muscular tube beginning at the epididymis and coursing into the pelvic cavity, terminating posterior to the urinary bladder.

    • Near its end, it dilates into the ampulla before narrowing again at the prostate to form the ejaculatory duct.

  • The vas deferens transports mature sperm from the epididymis; once sperm are produced in the testis, they rely on the ductus deferens and ejaculatory duct to propel them into the prostatic urethra and out during ejaculation.

Seminal Fluid Composition

  • Semen includes fluid from various structures:

    • Epididymis

    • Seminal vesicles

    • Prostate gland

    • Vas deferens

  • Each structure plays a crucial role in the production of seminal fluid, which supports sperm movement toward the ovum while keeping sperm nourished and protected.

Imaging the Prostate

  • The prostate can be imaged using two methods:

    • Transabdominal Imaging: Requires a full urinary bladder, with the patient lying supine.

      • The probe is angled approximately 30 degrees caudal, using the bladder as a window.

      • Slight compression can be applied for clearer imaging of the prostate's inferior portion.

    • Transrectal Imaging (TRUS):

      • The patient lies in a lateral decubitus position, with knees bent towards the chest.

      • Adequate gel must be applied before probe insertion, and a small amount of urine in the bladder can assist identification.

      • The prostate is imaged in both sagittal and transverse planes.

      • Volume measurement involves height and length in the sagittal plane, and width in the transverse plane, while also documenting the seminal vesicles and urinary bladder.

Prostate Pathology

Blood Test for Prostate Specific Antigen (PSA)

  • Definition:

    • PSA is a protein produced by the prostate and measurable through a blood test. Elevated levels can indicate:

    • Benign Prostatic Hyperplasia (BPH)

    • Prostate Cancer

    • Prostatitis

  • Normal PSA Ranges:

    • Men under 50: PSA < 2.5 ng/ml

    • Men between 50-59: PSA < 3.5 ng/ml

    • Men between 60-69: PSA < 4.5 ng/ml

    • Men older than 70: PSA < 6.5 ng/ml

Benign Prostatic Hyperplasia (BPH)

  • Definition:

    • Hyperplasia is the increase in the number of normal cells within an organ's tissues, specifically, a non-malignant enlargement of the prostate gland common in aging men.

  • Diagnosis:

    • Can be detected using a combination of methods:

    • Digital Rectal Exam (DRE)

    • Blood Test indicating PSA levels

    • Cystoscopy (examination through a cytoscope)

    • Ultrasound (TRUS or transabdominal)

    • Prostate biopsy (transrectal ultrasound-guided)

  • Clinical Symptoms of BPH:

    • Urinary frequency

    • Nocturia

    • Urinary urgency

    • Weak urinary flow

    • Dysuria

  • Symptoms Explained:

    • Pressure on the urethra from an enlarged prostate can lead to difficulty starting a urine flow and a weaker stream, causing dribbling or a sensation of incomplete bladder emptying after urination.

  • Serious Problems Include:

    • Urinary stasis

    • Urinary tract infections

    • Complete blockage of the urethra

    • Renal infection

    • Renal failure

  • Sonographic Findings for BPH:

    • Enlarged prostate gland

    • Possible cysts

    • Heterogeneous echotexture

    • Possible post-void residual

    • Possible calcifications

Prostatitis

  • Definition:

    • Often described as an infection of the prostate or an idiopathic inflammation. It can affect men of all ages.

  • Categories & Treatments:

    • 1. Acute bacterial prostatitis

    • 2. Chronic bacterial prostatitis

    • 3. Prostatodynia

    • 4. Asymptomatic inflammatory prostatitis

      • Categories 1 & 2: Antibiotics and pain relievers

      • Category 3: Symptomatic relief

      • Category 4: No treatment provided

  • Clinical Symptoms of Prostatitis:

    • Painful, difficult, and/or frequent urination

    • Hematuria (blood in urine)

    • Groin pain

    • Fever

    • Body aches

    • Penile discharge

Prostate Cancer

  • Definition:

    • Most common form of cancer in men (excluding skin cancer), with only one in 41 men dying from it.

    • Treatments include surgery, radiation, hormone therapy, and chemotherapy, with some men opting for watchful waiting (delaying treatment).

  • Adenocarcinoma:

    • Most prevalent form of prostate cancer, commonly seen in African American males over 50.

    • Often situated within the peripheral zone of the prostate and growth rate is typically slow with increased blood flow.

  • Clinical Symptoms of Prostate Cancer:

    • Early signs may include:

      • Frequent urination

      • Pain in the lower back, hips, or thighs

      • Weak urine flow

      • Difficulty achieving an erection

      • Blood in urine or semen

  • Sonographic Findings for Prostate Cancer:

    • Enlarged prostate

    • Hypoechoic mass

    • Possible calcifications

    • Hypervascularity

Ultrasound Guided Prostate Biopsy

  • A procedure to retrieve tissue samples from suspicious areas within the prostate.

    • Process:

    • A fine needle (often an 18g core biopsy gun, plus a 25-gauge needle for anesthetic) is utilized to collect several tissue samples (typically 6-12).

  • Urologist Role:

    • Urologists are specialized doctors who conduct these procedures.

  • Patient Preparation:

    • Medications that elevate bleeding risk should cease several days before the procedure.

    • A cleansing enema may be required before the procedure, and antibiotics are administered 30-60 minutes prior to mitigate infection risk.

  • Patient Positioning:

    • Lateral decubitus, facing away from the ultrasound machine, with knees bent towards the chest.

    • Expected Outcomes:

    • Bleeding and discomfort post-procedure; rest with no heavy lifting is advised.

Metastases

  • Common Metastatic Pathways:

    • Bone: - Spine metastasis is frequent.

    • Lymph: - Can spread to other organs.

    • Direct Invasion: - Involves nearby tissues like the rectum and bladder.

Treatment for Malignancy

  • Options include:

    • Radiation therapy

    • Brachytherapy

    • Chemotherapy

    • Cryosurgery

    • Hormone therapy

    • High-Intensity Focused Ultrasound (HIFU)

    • Radical prostatectomy.

    • Pitfalls:

    • Risks include incontinence and impotence post-treatment.


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