Prostate anatomy

tried to describe anatomy of prostate in a nutshell with few recent concepts

1. Prostate Anatomy Dr. Sambit Tripathy

2. I t is humbling to realise that even today basic anatomy may not be known or all understood. - patrick c walsh , 1998

3. Gros s Anatomy Ovoid (Almond) in shape. 3  cm in length, 4 cm in width, and 2 cm in depth. Weight of 18 to 20 g.   Homologous to the Skene glands. Composed of G landular elements (70%) Fibromuscular stroma (30%)

4. 3 cm 4 cm 2 cm

5. The base of the prostate is at the bladder-prostate junction. Apex is the narrowest and the most inferior portion of the prostate gland. Sits on urogenital diaphragm.  Palpable on DRE (~ 4 cm).

6. Apex continuous with the striated urethral sphincter.  It has 3 surfaces Anterior surface Posterior surface Lateral surfaces

7. Capsule of Prostate Composed of collagen, elastin , and smooth muscle. The capsule measures 0.5 mm in thickness posteriorly and laterally on average. No true prostatic capsule at Apex of the prostate (normal prostate glands are seen blending into the striated muscle of the urethral sphincter). At the base separating the prostate from the bladder, ( detrusor muscle fibers fuse with the capsule of the prostate).

8. Fascia and prostate attachments Three separate fascial structures surround the prostate. Denonvilliers ' fascia The prostatic fascia The endopelvic fascia

9. Denonvilliers ' fascia “The plane between wind and water” - R . Ger, 1988 Denonvilliers ' fascia lies posteriorly , adherent to the prostate, between it and the rectum. It also covers the posterior surface of the seminal vesicles. Denonvilliers ' fascia forms an important barrier to the spread of prostatic and rectal malignancy.

10. Prostatic fascia The prostatic fascia surrounds the prostate gland. Anteriorly and antero -laterally, it is in direct continuity with the fibromuscular stroma of the prostate. Laterally , it fuses with the endopelvic fascia. Posteriorly , it fuses with, and is indistinguishable from, Denonvilliers ' fascia.  

11. Endopelvic fascia Endopelvic fascia refers to the parietal pelvic fascia in the region of the prostate, overlying the levator ani muscle . The prostate capsule blends with the continuation of the endopelvic fascia on the anterior and anterolateral aspects of the prostate. The prostate receives its blood supply and autonomic innervation between the layers of endopelvic fascia and the prostatic fascia .

12. Detrusor apron and the puboprostatic ligaments The detrusor apron of Myers  is an extension of the longitudinal smooth muscle of the bladder ( detrusor ) anteriorly, in front of the anterior commissure (isthmus) of the prostate. It consists of a loose conglomeration of longitudinal smooth muscle bands and veins. Its thickness is greatest at the bladder neck in the mid-line . Laterally, it fuses with the fascial tendinous arch of the pelvis.

13. It represents a direct continuity of the anterior wall of the bladder with the pubis, via the puboprostatic ligaments, similar to that in the female. The superficial branch of the dorsal vein is positioned in the retropubic fat outside the prostatic fascia. It drains into the dorsal vein complex.

14. The levator ani's pubococcygeal portion hugs the lateral aspects of the prostate and is related to its overlying endopelvic fascia . The prostate capsule and the pelvic fascia separate below the parietal and visceral endopelvic fascia juncture ( arcus tendineus fascia pelvis).

15. Neurovascular bundle of Walsh Fatty, areolar tissue and the lateral branches of the dorsal vein complex take up the space of this separation between the prostate capsule and the pelvic fascia.  The cavernosal nerves travel within the parietal pelvic fascia, also known as the lateral prostatic fascia, posterolateral to the prostate.

16. Zones of prostate The prostate has been divided into distinct anatomic zones.  C an be identified with TRUS. T ransition zone Central zone Peripheral zone

17. Transition zone Transition zone is the smallest of the zones of the prostate. 5 % to 10 %. The transition zone is separated from the rest of the glandular compartments of the prostate by a distinct fibromuscular band. Benign prostatic hyperplasia most commonly occurs in the transition zone.

18. Central zone The central zone ducts are positioned circumferentially, surrounding the openings of the ejaculatory ducts. This zone expands toward the base of the bladder, surrounding the ejaculatory ducts, in the shape of a cone. The central zone comprises 25% of the glandular tissue of the prostate.

19. Peripheral zone The peripheral zone of the prostate is the largest zone (70%) .   Makes up the posterior and lateral aspects of the prostate gland. The ducts of the peripheral zone drain into the prostatic sinus along the entire length of the postsphincteric prostatic urethra. Seventy percent of prostate cancers are found in the peripheral zone.

20. Anterior fibromuscular stroma N on-glandular May comprise up to one third of the mass of the prostate. Composed of collagen, smooth and striated muscle, and elastin . It is anatomically continuous with the anterior visceral fascia, the anterior preprostatic sphincter, and the prostatic capsule.

21. Compartmentalized clinically, based on digital rectal examination and cystoscopic appearance. A central sulcus divides the two lateral lobes of the prostate and a middle lobe. The middle lobe may become hyperplastic and may extend into the bladder neck with age.

22. Histology The epithelial cells of the prostate glands are cuboidal or columnar. These epithelial cells have abundant secretory granules and are organized in rows with their apices projecting into the lumen and their bases attached to a basement membrane. The epithelial cells line the periphery of the acinus and secrete into the acinus , which drain into ducts to the urethra ultimately.

23. A thin layer of connective tissue and stromal smooth muscle surrounds each acinus . The stroma is composed of smooth muscle, which is rich in α- actin , myosin, and desmin . I t is also composed of collagen and is continuous with the prostatic capsule .

24. Arterial Supply The inferior vesical artery is the typical arterial supply to the prostate .  The inferior vesical artery branches into urethral arteries that enter the prostatovesical junction posterolaterally and course in a perpendicular route to the urethra. They travel toward the bladder neck with the largest branches posteriorly , approaching the bladder neck in the one o'clock to five o'clock positions and the seven o'clock to eleven o'clock positions.

25. They then supply the urethra after making a caudal turn to run parallel to the urethra. These branches supply the urethra, the periurethral glands, and the transition zone of the prostate.

26. The inferior vesical artery also branches into the capsular artery. The capsular artery yields small branches that supply the anterior prostatic capsule. The capsular branches enter the prostate at 90-degree angles and provide arterial supply to the glandular tissues.

27. Also supplied by banches from I nternal pudendal artery Middle rectal ( hemorrhoidal ) artery

28. Venous Drainage The prostate includes abundant venous drainage through the periprostatic plexus.  The periprostatic plexus anastomoses with the deep dorsal vein of the penis and the internal iliac ( hypogastric ) veins . Batson venous plexus  (or  Batson veins )   is a network of veins with no valves that connect deep pelvic veins draining the bladder,  prostate, and  rectum  to the internal vertebral venous plexus.

29. Lymphatic Drainage The obturator and internal iliac nodes are the primary sites of lymphatic drainage from the prostate.  The presacral group or, infrequently, the external iliac nodes may receive a small portion of the initial lymphatic drainage.

30. Nerve Supply The cavernous nerves provide sympathetic and parasympathetic innervation to the prostate from the pelvic plexus. Innervations to the glandular and stromal elements of the prostate are found traveling with branches of the capsular artery. Sympathetic fibers innervate the smooth muscle of the capsule and stroma for contraction.

31. The parasympathetic nerves promote secretory function by terminating in the acini . The pelvic plexuses carry afferent neurons from the prostate to the pelvic and thoracolumbar spinal centers.

32. DETRUSOR APRON In pictorial review of his operation, Walsh clearly demonstrated the existence of the obscuring tissue proximal to an underlying right-angle clamp and a single silk ligature to secure the dorsal vein complex. The tissue that obscures the prostate in part constitutes an extension of the anterior wall of the bladder beyond the point at which the bladder neck is formed. It is a detrusor apron, which has been described or illustrated, but has generally been unappreciated with respect to radical prostatectomy.

33. There continues to be a misconception in the minds of many urologists that the bladder ends anteriorly at the bladder neck. The mistaken concept, widely believed and illustrated, is of a bladder perched entirely on top of the prostate, like a hot air balloon with a gondola beneath. Furthermore , the puboprostatic ligaments are commonly shown attached directly to the anterior surface of the prostate with no bladder connection.

34. However, there is direct continuity of the anterior wall of the bladder with the pubis, similar to the female, and it should be illustrated that way. Understanding the detrusor apron should help urologists to perform radical prostatectomy with increased skill.