🔵 Prostate
Anatomy, urethra, sphincters, BPH, prostate cancer, prostatitis — LUTS, TURP syndrome, PSA, Gleason grading, staging.
Prostate Anatomy
Overview
The prostate is a walnut-sized exocrine gland (approximately 20 g) situated between the bladder neck and the external urethral sphincter. It surrounds the proximal urethra. The rectum lies posteriorly, which is why digital rectal examination (DRE) allows palpation of the posterior surface.
| Feature | Detail |
|---|---|
| Size | ~20 g; 3 × 4 × 2 cm |
| Location | Between bladder neck (superior) and external urethral sphincter (inferior) |
| Posterior relation | Rectum (separated by Denonvilliers’ fascia) — permits DRE |
| Anterior relation | Retropubic space (of Retzius), pubic symphysis |
| Superior relation | Bladder base; seminal vesicles enter posterosuperiorly |
| Inferior relation | Urogenital diaphragm / pelvic floor |
The prostate has four anatomical zones. Knowing which pathology arises in which zone is high-yield for MRCS.
- No glandular tissue
- Composed of smooth muscle and fibrous stroma
- Not a site of pathology
- Surrounds the ejaculatory ducts
- Resistant to pathology
- Rarely involved in BPH or cancer
- Surrounds the prostatic urethra
- Site of BPH — can become the dominant zone
- ~20% of prostate cancers arise here
- Largest zone; palpable on DRE
- Site of ~80% of prostate cancers
- Site of prostatitis
Clinical Relevance — Zones
BPH → Transitional zone: enlargement compresses the prostatic urethra causing LUTS. TURP resects this zone.
Cancer → Peripheral zone: palpable on DRE as a hard, irregular nodule; not typically felt early when in the transitional zone — hence importance of PSA screening.
| Feature | Detail |
|---|---|
| Arterial supply | Inferior vesical artery (branch of internal iliac artery) — also supplies inferior bladder and prostatic urethra |
| Venous drainage | Prostatic venous plexus (of Santorini) → internal iliac veins. Communicates with Batson’s vertebral venous plexus — explaining vertebral metastases in prostate cancer |
| Lymphatic drainage | Obturator and internal iliac nodes primarily; also external iliac nodes |
| Female equivalent | Inferior vesical artery is replaced by the vaginal artery, which also gives the uterine artery |
Batson’s Venous Plexus
The prostatic venous plexus communicates with Batson’s paravertebral venous plexus — a valveless network surrounding the spine. This allows retrograde spread of prostate cancer to vertebrae, classically causing osteosclerotic (bone-forming) metastases in the lumbar spine and pelvis. Raised ALP with bone pain and a raised PSA = bone metastases until proven otherwise.
Physiology
The prostate secretes prostatic fluid, which forms ~30% of seminal volume. Prostatic fluid is:
- Rich in zinc, citrate, and acid phosphatase
- Contains PSA (prostate-specific antigen) — a serine protease that liquefies semen after ejaculation
- Slightly acidic (pH ~6.5), but the overall semen pH is alkaline due to seminal vesicle secretions
Prostatic secretion is under androgen (testosterone/DHT) control — the basis for hormonal therapies in BPH and prostate cancer.