Which of the following zones of the prostate is most commonly affected in benign prostatic hyperplasia?

Explanation

## Anatomical Zones of the Prostate and BPH ### Zonal Anatomy The prostate is divided into three glandular zones based on embryological origin and histological characteristics: | Zone | Percentage of Normal Prostate | Embryological Origin | BPH Involvement | |------|-------------------------------|----------------------|------------------| | **Peripheral Zone** | 70% | Urogenital sinus | Rarely affected in BPH | | **Transition Zone** | 5–10% | Urogenital sinus | **Primary site of BPH (90% of cases)** | | **Central Zone** | 20–25% | Mesonephric ducts | Rarely affected in BPH | | **Anterior Fibromuscular Stroma** | Non-glandular | — | Not involved in BPH | ### Key Point: Transition Zone Hyperplasia **High-Yield:** The transition zone (TZ) surrounds the proximal urethra and accounts for ~90% of clinically significant BPH, despite comprising only 5–10% of the normal prostate volume. This small zone is responsible for most lower urinary tract symptoms. ### Clinical Significance **Clinical Pearl:** Transition zone enlargement directly compresses the urethra, causing outlet obstruction and LUTS. This is why prostate volume correlates better with symptoms than PSA level. ### Contrast with Prostate Cancer - **Peripheral zone:** Site of 70% of prostate cancers (different from BPH) - **Transition zone:** Site of only 20–30% of prostate cancers - This anatomical distinction is crucial for DRE interpretation and biopsy strategy **Mnemonic:** **TZ in BPH** — **T**ransition **Z**one is the site of **B**enign **P**rostatic **H**yperplasia. [cite:Robbins 10e Ch 20]