Mills Ch35 Prostate

966

SECTION IX : GenitourinaryTract

An oblique coronal section (Fig. 35.5) along the proximal (mid to base) segment of the prostatic urethra from verumon- tanum to the bladder neck best defines its glandular relation- ships. Normally, the proximal urethral segment is intimately related to about only 5% of the prostatic glandular tissue, and almost all of this is the transition zone (7). This zone is formed by two small lobes whose ducts leave the posterolat- eral recesses of the urethral wall at a single point. The main ducts of the transition zone extend laterally and curve sharply anteriorly, arborizing toward the bladder neck. The main nonglandular tissue of the prostate is the ante- rior fibromuscular stroma which overlies the urethra in the anteromedial prostate. Its bulk and consistency vary consider- ably from apex to base, as described further in this chapter. Radical prostatectomy, including removal of the seminal vesicles, is the definitive surgical procedure for patients with prostatic carcinoma. Current convention calls for inking the intact prostate gland and seminal vesicles in two colors in the fresh state to allow assessment of laterality. The most apical region of the gland (approximately 5 mm) is amputated in a transverse plane to include the opening of the distal ure- thra, and then subsequently sectioned parasagittally, perpen- dicular to the inked surface (Fig. 35.6) for embedding. This allows for visualization of apical prostatic tissue in planes that are near perpendicular to the true apical surface and hence, more accurate evaluation of cancer penetration and margin status. Handling of the bladder neck margin may be FIGURE 35.5  Oblique coronal section diagram of prostate showing location of peripheral zone ( PZ ) and transition zone ( TZ ) in relation to proximal urethral segment ( UP ), verumontanum ( V ), preprostatic sphincter ( s ), bladder neck ( bn ), anterior fibromuscular stroma ( fm ), and periurethral region with periurethral glands. Branching pattern of prostatic ducts is indicated: the medial transition zone ducts penetrate into the sphincter. SECTIONING OF RADICAL PROSTATECTOMY SPECIMENS

verumontanum protrudes from the posterior urethral wall at the point of angulation and is the point at which the ejacu- latory ducts empty into the prostatic urethra. The ejacula- tory ducts then extend proximally from the verumontanum (mid) to the base of the prostate, following a course that is nearly a direct extension of the long axis of the distal (apex to mid) urethral segment, although usually offset posteriorly by a few millimeters. A coronal plane of section (Fig. 35.4) along the course of the ejaculatory ducts and distal (apex to mid) urethral segment provides the best demonstration of the anatomic relationships between the two major regions of glandular prostate, the peripheral and central zones (6). The periph- eral zone comprises about 65% of the mass of the normal glandular prostate. Its ducts exit posterolaterally from the urethral wall along a double row extending from the veru- montanum to the prostate apex. The ducts extend mainly laterally in the coronal plane, with branches that curve anteriorly and posteriorly. The central zone comprises about 30% of the glandular prostate mass. Its ducts arise in a small focus on the veru- montanum and immediately surround the ejaculatory duct orifices. The ducts branch directly toward the base of the prostate along the course of the ejaculatory ducts, fanning out to form an inverted conical structure that is flattened in the anterior–posterior plane. The base of this cone comprises almost the entire base of the prostate. The most lateral central zone ducts run parallel to the most proximal (base) peripheral zone ducts, separated only by a narrow band of stroma, which is usually imperceptible in clinical specimens. FIGURE 35.4  Coronal section diagram of prostate showing location of central zone ( CZ ) and peripheral zone ( PZ ) in relation to the distal urethral segment ( UD ), verumontanum ( V ), and ejaculatory ducts ( E ). The branching pattern of prostatic ducts is indicated; subsidiary ducts provide uniform density of acini along the entire main duct course.