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I. Basic Principles: Prostate Anatomy
ANATOMY OF THE PROSTATE
Detailed understanding of prostatic anatomy is essential for every urologist.
Figure 1: Prostate Anatomy
PS=pubic symphisis AFS=anterior fibromuscular stroma SV=seminal vesicle CZ, TZ, PZ=zones of prostate (see text)
- In a young adult, prostate weights ~20g and measures ~3 by 4 by 2 cm
- Apex = inferior portion of prostate, continuous with striated sphincter. Base = superior portion and continuous with bladder neck.
- Prostatic urethra
- Covered by transitional epithelium
- Hugs anterior portion of gland
- Makes a ~30 degree bend in its mid portion (degree of angulation can vary from 0 to 90 degrees)
- just distal to urethral angulation
- ejaculatory ducts (union of seminal vesicles and each vas deferens) drain to each side of prostatic utricle (vestigial Mullerian duct structure)
- Zones of Prostate (Figure 1)
- Central zone (CZ)
- Cone shaped region that surround the ejaculatory ducts (extends from bladder base to the veru)
- Likely stems from Wolffian ducts
- 25% of glandular tissue in young adults
- Only 1-5% of prostate cancer from this region (likely because of Wolffian duct embryologic origin)
- Peripheral zone (PZ)
- Posteriolateral prostate
- Mesodermal in origin
- Majority of prostatic glandular tissue
- Origin of up to 70% of prostate adenocarcinoma
- Transitional zone (TZ)
- Surrounds the prostatic urethra proximal to the veru (aka preprostatic urethra)
- Endodermal in origin
- In young men, accounts for only 5-10% of prostatic glandular tissue.
- Only ~20% of prostate cancer arise from TZ
- Gives rise to BPH
- Central zone (CZ)
- "Lobes" of the prostate
- Enlargement of periuthral tissue in the TZ results in hyperplasia of "lateral lobes" (Figure 2).
- In some men, hyperplasia of periurethral glands of the TZ at the bladder neck produces a "median lobe" -- tissue mass that can ball-valve into the outlet (Figure 3)
Figure 2: Cystoscopic view of lateral lobes.
Edge of the verumontanum is seen at 6 o'clock.
Figure 3: Cystoscopic view of a large median lobe.
The ball-valve obstruction created by a median lobe in some men is clearly appreciated from this image.