Mills Ch35 Prostate

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CHAPTER 35:  Prostate

FIGURE 35.10  The verumontanum often contains densely packed prostatic glands lined by benign secretory cells, often with abundant intraluminal corpora amylacea.

ejaculation to prevent retrograde flow of seminal fluid from the distal urethral segment and may have resting tone that maintains closure of the proximal urethral segment (18). At the base, the glands of the transition zone gradually recede and the few remaining peripheral zone acini once again comprise the anterior glandular tissue. In contrast with its apical appearance, however, the peripheral zone rarely extends anteromedially due to the abundant stroma in this region. This stroma appears as an expansive strip of tissue consisting of both preprostatic sphincter and anterior fibro- muscular stroma, with the latter often merging with large smooth muscle bundles located in the anterior extraprostatic space. With increasing angulation, the prostatic urethra is identified further anteriorly in histologic sections, eventually breaching the anterior-most border of tissue sections at the level of the bladder neck. Posteriorly and posterolaterally, the central zone becomes evident surrounding the ejacula- tory ducts which themselves are immediately encircled by a sheath of loose fibrous tissue with abundant lymphovascular spaces (Fig. 35.13). In the most basal portions of the gland, the well-formed muscular coat at the base of the seminal vesicles emerges and separates from the bulk of the pros- tatic tissue creating a fibroadipose tissue septum. The last vestiges of the central zone are present at the most lateral aspects of these emerging seminal vesicles (14). FIGURE 35.12  Preprostatic sphincter investing the proximal urethra in section from the base of prostate. The sphincter is composed of com- pact, short smooth muscle fibers distinct from prostatic smooth muscle and conveying a paler appearance to the periurethral zone as seen in Figure 35.11. Nonglandular Components of Prostatic and Extraprostatic Tissues Prostatic Capsule and Anterior Fibromuscular Stroma The prostatic “capsule” or condensed fibromuscular tissue (Fig. 35.14) ideally consists of an inner layer of smooth mus- cle fibers and an outer collagenous membrane. However, the relative and absolute amounts of fibrous and muscle

density of glandular tissue in the mid gland coupled with effects of organ contraction (14). Basal One-Third of the Prostate (Base) Progressing proximally from mid gland to base, the urethra becomes invested by a thick layer of short smooth muscle fibers, constituting the “preprostatic sphincter” (Figs. 35.11 and 35.12), which at its most lateral point may be in con- tact with the glands and acini of the transition zone (5,7). The preprostatic sphincter is thought to function during

FIGURE 35.11  Whole mount section from base of prostate. The prepro- static sphincter ( PPS ) is evident as a pale area surrounding the proxi- mal urethra. The transition zone ( TZ ) shows abortive small acini and is covered anteriorly by a vast anterior fibromuscular stroma ( AFMS ) which merges with smooth muscle bundles in the anterior extrapros- tatic space ( AEPS ). Posteriorly, the expansive central zone ( CZ ) sur- rounds the ejaculatory duct complex ( EJD ), while some peripheral zone ( PZ ) is still apparent posterolaterally.