Zonal anatomy of prostate

The zonal anatomy of the prostate (McNeal's zonal anatomy model) refers to the anatomical classification system proposed by McNeal in 1981, which divides the prostate gland into four distinct regions based on their histological, embryological, and biological characteristics. This model replaced the earlier lobar classification (Lowsley) and remains the standard framework for understanding prostate physiology and pathology.

The Four Zones

• Peripheral Zone (PZ) The largest glandular region, comprising approximately 70% of the glandular prostate. Its ducts radiate laterally from the urethra, extending from the verumontanum to the apex along the posterior and posterolateral surfaces. It is derived from the urogenital sinus and is composed of simple, small rounded glands with loose stroma. The PZ is the most common site of origin for prostate adenocarcinoma (~70% of cases), as well as chronic prostatitis and postinflammatory atrophy.

• Central Zone (CZ) A cone-shaped structure accounting for approximately 25% of the glandular tissue. Its ducts arise near the ejaculatory duct orifices at the verumontanum and fan out toward the base, surrounding the ejaculatory ducts. It is derived from the Wolffian duct and is histologically distinct, with complex, large polygonal glands and compact stroma. The CZ has a very low incidence of carcinoma (~5%) and rarely develops disease.

• Transition Zone (TZ) The smallest glandular region, comprising only about 5% of the normal glandular tissue. It consists of two small lobules flanking the proximal prostatic urethra just superior to the verumontanum, with ducts extending laterally and curving anteriorly. Derived from the urogenital sinus, it has simple, small rounded glands with fibromuscular stroma. The TZ is the exclusive site of origin of benign prostatic hyperplasia (BPH) and accounts for approximately 25% of prostate cancers.

• Anterior Fibromuscular Stroma (AFS) A thick, non-glandular region forming the entire anterior surface of the prostate. It is composed of fibrous and smooth muscular elements (with striated muscle in its apical half) and is devoid of glandular tissue. It serves as a structural "apron" shielding the glandular zones anteriorly.