Prostate Anatomy: Overview, Gross Anatomy, Microscopic Anatomy (2025)

Overview

Embryologically, the prostate, seminal vesicles, and ductus (vas) deferens originate from two separate structures. The prostate arises from a budding collection of tissues in the urogenital sinus. The seminal vesicles and the ductus deferens are formed from the mesonephric duct.

The prostate develops from the interactions between the urogenital sinus mesenchyme associated with the mesonephric and paramesonephric ducts and the endoderm of the proximal part of the urethra (the Müllerian duct-urogenital sinus junction).^[1]The epithelial outgrowths form the prostatic segment of the urethra that grows into the surrounding mesenchyme. This outgrowth and branching start at week 10 during embryo growth; by week 12, there are five groups of tubules that form the lobes of the prostate. The first group makes up the middle lobe; the second and third groups make up the right and left lateral lobes; the fourth group is the posterior lobe that starts from the floor of the urethra; and the fifth group is the anterior lobe.

This traditional lobar anatomy has largely been superseded by a zonal classification proposed by McNeal, which is more clinically relevant. The prostate is divided into three glandular zones (peripheral, central, and transition zones)and a nonglandular anterior fibromuscular stroma. The peripheral and transition zones develop from the urogenital sinus, while the central zone originates from mesonephric duct tissue.^{[1, 2]}

The following image depicts the posterior view of the prostate gland.

Prostate gland, posterior view.

Gross Anatomy

A normal prostate gland is approximately 20 g in volume, 3 cm in length, 4 cm wide, and 2 cm in depth. As males get older, the prostate gland is variable in size secondary tobenign prostatic hyperplasia (BPH). The gland is located posterior to the pubic symphysis, superior to the perineal membrane, inferior to the bladder, and anterior to the rectum (see the image below). The base of the prostate is in continuity with the bladder and the prostate ends at the apex before becoming the striated external urethral sphincter. The sphincter is a vertically oriented tubular sheath that surrounds the membranous urethra and prostate.

Prostate gland, posterior view.

The prostate is enclosed by a capsule composed of collagen, elastin, and large amounts of smooth muscle. The prostate is covered by three distinct layers of fascia on the anterior, lateral, and posterior aspects. Studies have described multiple layers of fascia, which may allow separation oflayers containing nerve fibers without dissecting into prostate tissues.^[3]The preservation of lateral prostatic fascia is crucial during procedures such as robotic-assisted radical prostatectomy (RALP).^[4]The anterior and anterolateral fascia is in direct continuity of the true capsule; this is the location of the deep dorsal vein of the penis and its tributaries. Laterally, the fascia fuses with the levator fascia. The outer longitudinal fibers of the detrusor muscle fuse and blend with the fibromuscular tissue of the capsule. The posterior aspect is covered by the rectovesical (Denonvilliers) fascia.

Microscopic Anatomy

Historically, the prostate has been divided into three zones: (1) transition zone, (2) central zone, and (3) peripheral zone. The transition zone accounts for 10% of the prostatic glandular tissue and 20% of the adenocarcinomas. The prostate consists of approximately 70% glandular tissue and 30% fibromuscular stroma.

Transition Zone

The transition zone of the prostate is a small region surrounding the prostatic urethra, located between the bladder neck and the verumontanum. In young males, it constitutes approximately 5-10% of the prostate's glandular tissue but can expand significantly with age due to BPH, often becoming the largest zone in older males.^[2]

The prostatic urethra courses the length of the prostate from the level of the bladder neck to the level of the membranous urethra. The epithelium consists of transitional cells similar to bladder epithelium.

The transition zone extends from the base of the prostate near the bladder to the verumontanum and is encircled posteriorly by the central zone.^[4]

This transitional zone is where BPH occurs and can lead to bladder outlet obstruction when an adenoma grows to a significant size. When the adenoma grows large enough, it can compress the fibromuscular band surrounding this zone, creating a surgical capsule.

The transitional zone is often described as having two lateral lobes and a median lobe that lead to symptoms of the lower urinary tract symptoms. A urethral crest runs along the posterior midline and disappears at the membranous urethra. On both sides of the urethral crest, there is a grove where the prostatic sinuses exist and drain all of the glandular elements.

The urethral crest widens and protrudes from the posterior wall as the seminal colliculus (verumontanum). A small midline pit, the prostatic utricle, is found at the apex of the seminal colliculus. On either side of the utricular orifice, small slit-like openings to the ejaculatory duct are found.

Approximately 20-30% of prostate cancers originate in the transition zone, though this is less common compared with cancers arising in the peripheral zone. Tumors in the transition zone are often associated with lower Gleason scores and better prognoses compared with tumors in other zones.^[5]

Central Zone

The central zone is the area surrounding the ejaculatory ducts. This zone consists of 25% of glandular tissue. It is located posterior to the transition zone and proximal to the verumontanum, extending from the base of the prostate toward the mid-urethra.^[6]

The central zone is embryologically derived from the Wolffian duct, distinguishing it from other prostatic zones, which are derived from the urogenital sinus.^[6]

Histologically, it contains large caliber glands with a characteristic "Roman bridge" architecture, a prominent basal cell layer, and tall columnar cells with an eosinophilic cytoplasm.^[6]

Very few adenocarcinomas are found in this region and can represent as little as 1-5% of these tumors in the prostate. However, when present, these cancers tend to exhibit more aggressive behavior and are more likely to invade adjacent structures such as seminal vesicles.^[7]

Peripheral Zone

The peripheral zone of the prostate constitutes 70% of glandular tissue. It is the largest zone of the prostate. It is situated on the posterior and lateral aspects of the prostate, forming a disc-like structure whose ducts radiate laterally from the urethra distal to the verumontanum.^[1]

This zone demonstrates high citrate content, which plays a role in its imaging characteristics and susceptibility to conditions such as cancer and inflammation.^[8]

The peripheral zone is the area that is palpated on digital rectal examination (DRE) and represents the area where 70% of adenocarcinomas are found. This area is also the location most commonly affected by chronic prostatitis

Arterial Supply

Arterial supply to the prostate is primarily from the inferior vesical artery, which originates from the anterior division of the internal iliac (hypogastric) artery. Anatomical variations are common, and prostatic arteries may arise from other sources such as the internal pudendal artery, middle rectal artery, or even accessory branches such as the obturator artery or superior vesical artery. These variations are significant for clinical procedures such as prostatic artery embolization and emphasize the importance of individualized vascular mapping.

The inferior vesical artery branches into two main arterial branches to feed the prostate. The prostatic vessels and the autonomic innervations run between the layers of the lateral prostatic fascia and the prostate. The inferior vesical artery supplies the base of the bladder, the distal ureters, and the prostate.

The first arterial branch is the urethral artery that enters the prostatovesical junction posterolaterally and travels inward perpendicular to the urethra toward the bladder neck at approximately the 5 o'clock and 7 o'clock meridian. The urethral artery then turns caudally and parallel to the urethra to supply the transition zone. This artery is the main arterial supply for the adenomas in BPH.

The capsular artery is the second main branch of the prostate. It runs posterolateral to the prostate with the cavernous nerves. This artery enters the prostate at right angles to supply the glandular tissue.

Arterial blood supply to the seminal vessels and ductus deferens comes from the deferential artery or artery of the ductus, a branch from the superior vesical artery.^[9]

Venous Drainage

Venous drainage of the prostate starts with the deep dorsal vein, which leaves the penis under the deep penile (Buck) fascia between the corpora cavernosa and then under the pubic arch. This vein then passes anterosuperior to the perineal membrane and divides into three major branches, the superficial branch and the right and left branches.

The superficial branch travels between the puboprostatic ligaments and lies on top of the prostate and bladder neck. The superficial branch is outside the anterior prostatic fascia in the retropubic fat and pierces the fascia to drain into the dorsal venous complex. The common trunk of the dorsal venous complex and the lateral venous plexuses are covered by the anterior prostatic fascia and the endopelvic fascia. The lateral plexuses travel posterolaterally and communicate with the pudendal, obturator, and vesical plexus. These veins then communicate with the internal iliac vein.

Innervations

The autonomic innervations of the prostate arise from the pelvic plexuses formed by the parasympathetic, visceral, efferent, and preganglionic fibers that arise from the sacral levels (S2-S4) and the sympathetic fibers from the thoracolumbar levels (L1-L2). The pelvic plexus is located beside the rectum approximately 7 cm from the anal verge, with its midpoint located at the level of the tips of the seminal vesicles.

The sympathetic and parasympathetic fibers that come from the pelvic plexuses travel to the prostate via the cavernous nerves. The cavernous nerves run posterolateral to the prostate in the lateral prostatic fascia. Two thirds of the nerve fibers run along the traditional posterolateral aspect of the prostate; however, studies on surgical anatomy of the prostate have demonstratedthat the remaining third of the nerve fibers are more anterior in theanterior lateral aspect of the prostate.^[10]This has resultedin the "Veil of Aphrodite" technique of nerve preservation to maximize the number of nerves preserved during radical prostatectomy.^[11]The parasympathetic nerves end at the acini and lead to prostatic secretion. The sympathetic nerves lead to contraction of the smooth muscle of the capsule and the stroma.

The pudendal nerve is the major nerve supply leading to somatic innervations of the striated sphincter and the levator ani. The preprostatic sphincter and the vesicle neck or internal sphincter are under alpha-adrenergic control.

Lymphatic Drainage

Lymphatic drainage of the prostate primarily drains to the internal iliac, sacral, and the obturator lymphatic channels. There is also lymphatic communication with the external iliac, presacral, and the para-aortic lymph nodes.

This pathway is particularly significant to understand the spread of prostate cancer.^[12]

The lymphatic network of the prostate also demonstrates significant anastomoses with neighboring structures, such as the bladder and rectum, which can influence patterns of cancer dissemination. Anatomical studies have emphasized that traditional nodal templates used in clinical practice may not fully encompass all relevant drainage pathways, particularly posterior routes to sacral nodes. This has implications for surgical and radiological interventions aimed at managing prostate cancer.^[13]

Role in Continence

The mechanisms controlling urinary continence require several coordinated events.

Bladder Neck and Internal Sphincter: The bladder neck plays a critical role in continence by maintaining closure during the filling phase of micturition. This region includes smooth muscle fibers forming the internal urethral sphincter, which is an extension of the circular smooth muscle of the vesical neck. It is innervated by sympathetic fibers via the hypogastric nerve and pelvic plexus, which increase smooth muscle tone to prevent urine leakage during bladder filling.^[14]

External Urethral Sphincter: The external urethral sphincter is a cylindrical structure composed predominantly of slow-twitch striated muscle fibers. It extends from the apex of the prostate to the perineal membrane and is under voluntary control. This sphincter provides active continence through sustained contraction during periods of increased intra-abdominal pressure such as coughing or sneezing.^{[1, 4]}

Levator Ani Muscles: The levator ani muscle group, particularly the puborectalis and pubococcygeus components, forms a supportive sling around the urethra and prostate. These muscles contribute to continence by creating a urogenital hiatus that supports the sphincteric urethra. Voluntary contraction of these muscles enhances urethral closure pressure, especially during activities requiring additional continence control.^[15]

Periprostatic Structures: The puboprostatic ligaments and surrounding fibrous tissues, such as Denonvilliers' fascia and the detrusor apron, provide structural support to the prostate and urethra. These structures help maintain alignment and stability of the lower urinary tract, further aiding in continence.^{[1, 15]}

Urethral Support Mechanism: Studies highlight the importance of pelvic floor muscles such as the puboperinealis and rectourethralis in forming a "sling" around the urethra. This sling mechanism stabilizes the urethra during stress events and contributes to overall urinary control.^[15]

Preservation of these anatomical structures during surgical procedures such as radical prostatectomy is crucial for maintaining postoperative continence. Techniques such as bladder neck preservation and nerve-sparing approaches have been shown to improve early recovery of urinary control. Pelvic floor muscle training, including Kegel exercises, has demonstrated efficacy in enhancing continence outcomes postoperatively by strengthening these critical muscles.^[16]