Mills Ch35 Prostate

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CHAPTER 35:  Prostate

GENERAL TOPOGRAPHIC RELATIONSHIPS: McNEAL’S ZONAL ANATOMY

The human prostate gland is a composite organ, comprised of several glandular and nonglandular components. These different “zones” are tightly fused together within a com- mon sheath of fibromuscular tissue—the “capsule”—such that gross dissection is not possible. In a series of elegant dissections in postmortem specimens, Dr. McNeal showed that anatomic relationships are best demonstrated by exam- ination of cut sections in the sagittal, coronal, and oblique coronal planes (3,4). From these studies, it is evident that: (a) there are three distinct glandular regions: the peripheral, central, and transition zones; and (b) the main nonglandu- lar tissue of the prostate, termed the anterior fibromuscular stroma, is concentrated anteromedially and is responsible for much of the anterior convexity of the organ. The urethra is a primary reference point for describing anatomic relationships. Visualized in a sagittal plane of sec- tion (Fig. 35.3), the prostatic urethra is divided into proxi- mal and distal segments of approximately equal length by an anterior angulation at the midpoint between the prostate apex (distal) and the bladder neck (proximal) (1,5). The

FIGURE 35.1  Embryonic prostate, age 9 weeks, in the sagittal plane of the pelvis. Urethra (narrow central lumen) is angulated to the right at the midpoint, where the ejaculatory duct approaches from above left. A vertical strip of highly condensed prostate mesenchyme contacts the posterior urethral wall only distal to the ejaculatory ducts. The prostate is flanked by the rectum ( left ) and pubis ( right ). Duct buds have not yet formed.

FIGURE 35.3  Sagittal diagram of distal prostatic urethral segment ( UD ), proximal urethral segment ( UP ), and ejaculatory ducts ( E ) showing their relationships to a sagittal section of the anteromedial nonglandular tissues (bladder neck [ bn ]; anterior fibromuscular stroma [ fm ]; prepro- static sphincter [ s ]; distal semicircular [“striated”] sphincter [ s ]). These structures are shown in relation to a three-dimensional representation of the glandular prostate (central zone [ CZ ]; peripheral zone [ PZ ]; tran- sition zone [ TZ ]). Coronal plane ( C ) of Figure 35.4 and oblique coronal plane ( OC ) of Figure 35.5 are indicated by arrows .

FIGURE 35.2  Prepubertal prostatic duct lined by epithelium with multiple layers of nuclei and showing no cytoplasmic differentiation.