A 68-year-old man presents with progressive lower urinary tract symptoms including nocturia, weak stream, and incomplete emptying for the past 2 years. Digital rectal examination reveals a smooth, firm, symmetrically enlarged prostate. Which of the following is the most common histological zone of origin for benign prostatic hyperplasia?

Explanation

## Anatomical Zones of the Prostate The prostate is divided into three main histological zones based on McNeal's zonal anatomy: | Zone | Proportion of Normal Prostate | BPH Origin | Clinical Significance | |------|-------------------------------|-----------|----------------------| | **Transition zone** | 5–10% | **95% of BPH cases** | Surrounds urethra; causes LUTS | | **Central zone** | 25% | Rare | Rarely involved in BPH | | **Peripheral zone** | 65–70% | Rare in BPH | Common site of prostate cancer | | **Anterior fibromuscular stroma** | Variable | Not involved | Fibrous tissue, not glandular | **Key Point:** The transition zone is the most common site of benign prostatic hyperplasia, accounting for approximately 95% of all BPH cases. This zone surrounds the proximal urethra and, when enlarged, directly compresses the urethra and causes lower urinary tract symptoms. **High-Yield:** BPH arises from hyperplasia of both epithelial and stromal elements in the transition zone. The enlarged glandular and smooth muscle tissue progressively obstructs urinary flow, leading to symptoms such as nocturia, weak stream, hesitancy, and incomplete emptying. **Clinical Pearl:** While the peripheral zone comprises 65–70% of the normal prostate, it is rarely the site of BPH origin. However, the peripheral zone is the most common site of prostate cancer development — a clinically important distinction for digital rectal examination and biopsy planning. **Mnemonic:** BPH = **T**ransition zone (Think: **T**ransition = **T**urbine blocking the urethra) [cite:Harrison 21e Ch 297]