Mills Ch35 Prostate

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CHAPTER 35:  Prostate

cytologic atypia may be present in paraganglia, which could be confused with carcinoma, particularly in rare examples of intraprostatic paraganglia. Before supplying the corpora cavernosa, nerve branches leave the neurovascular bundle at the prostate apex in the very small inferior pedicle and penetrate the capsule directly in a small “apical insertion area” located laterally and posterolaterally (26). Here the distance from neurovas- cular bundle to prostate capsule is narrowed to only a few millimeters and hence sparing the nerves involved in erec- tile function requires dissecting very close to the prostatic capsule in this region (28,29). Arterial branches follow the nerve branches from the neurovascular bundle; they spread over the prostate sur- face and penetrate the capsule to extend directly inward toward the distal (apex to mid) urethral segment between the radiating duct systems of the central and peripheral zones (30,31). A major arterial branch enters the prostate at each side of the bladder neck and runs toward the veru- montanum parallel to the course of the proximal (mid to base) urethral segment. It supplies the periurethral region and medial transition zone. Architectural Patterns The biologic role of the prostate calls for the slow accumu- lation and occasional rapid expulsion of small volumes of fluid. These requirements are optimally met by a muscu- lar organ having a large storage capacity and low secretory capacity. It is fitting then that the prostatic ducts are mor- phologically identical to the acini except for their geom- etry, and both appear to function as distensible secretory reservoirs. Within each prostate zone, the entire duct–acinar system, except for the main ducts near the urethra, is lined by columnar secretory cells of identical appearance between ducts and acini. Immunohistochemical staining for prostate-specific antigen (PSA) and prostatic acid phos- phatase (PAP) shows uniform granular staining of all ductal and acinar cells (Fig. 35.21). Except for the main transition zone ducts, which termi- nate at the anterior fibromuscular stroma, the main ducts of the prostate originate at the urethra and terminate near the capsule (3,6,7) (Figs. 35.4 and 35.5). Since ducts and acini within each zone have a similar caliber, spacing, and histo- logic appearance, ducts, ductules, and acini cannot reliably be distinguished microscopically. Hence, abnormalities of architectural pattern such as those seen in adenosis, pros- tatic intraepithelial neoplasia (PIN), and prostatic carci- noma are identified in routine sections mainly by deviations from normal size and spacing of glandular units. The main excretory duct orifices of the peripheral zone arise every 2 mm from the distal (apex to mid) urethral ARCHITECTURAL AND CYTOLOGIC FEATURES OF THE GLANDULAR PROSTATE

FIGURE 35.21  Ducts and acini of peripheral zone, immunohistochemi- cally stained with anti-PSA and showing uniform distribution of protein throughout the cytoplasm of all ducts and acini.

segment along a double lateral line. A cluster of three or four subsidiary ducts arise about every 2 mm along each main excretory duct from urethra to capsule. These sub- sidiary ducts branch and extend only a short distance, rebranching and giving rise to groups of acini (Fig. 35.22). Hence, acini tend to be distributed with nearly uniform density along the course of the main duct between urethra and capsule, except that no acini are found immediately adjacent to the urethra. In the peripheral zone and transition zone, ducts and acini have simple rounded contours that are not perfectly circular because of prominent undulations of the epithelial border (4,6). The undulations presumably allow expansion of the lumina as secretory reservoirs. Central zone ducts and acini are distinctively larger than those of the peripheral zone and transition zone (Fig. 35.23). Both ducts and acini of the central zone become progres- sively larger toward the capsule at the prostate base reflect- ing the great expansion of central zone cross-sectional area from a small focus on the verumontanum to almost the entire prostate base. The corrugations in central zone duct/ acinar walls are often exaggerated into distinctive intraluminal ridges—so-called “Roman arches.” In some specimens, there is an evident contrast in stromal morphology that delineates the boundary between peripheral zone and transition zone (21). The transition zone stroma is composed of compact interlacing smooth muscle bundles. This stromal density differs from the adjacent loose