Anatomy of prostate gland, Benign prostatic hyperplasia and Carcinoma of the prostate.
Prostate gland is a partly glandular and partly fibromuscular organ.It is a gland of male reproductive system. It provides about 30% of volume of seminal fluid. Seminal fluid is produced by testis, prostate gland and seminal vesicle. It's female homologue is the small group of para urethral glands.
It lies beneath the bladder and above the urogenital diaphragm.
It is normally broader than it is long. The size is approximately 4 x 3 x 2 cm.It is inverted pyramid in shape. It has base, apex, anterior surface, posterior surface and two inferolateral surfaces.
It is the upper surface and fused with the neck of the bladder. It is penetrated by urethra which traverse the whole length of the gland.
The blunt apex is the lowest part. The urethra emerges from front of the apex and become as membranous part of the urethra which is surrounded by urethral sphincter.
Anterior surface is at the back of the retropubic space. It is connected to the bodies of the pubic bones by the puboprostatic ligaments.
The infetolateral surfaces are clasped by the pubourethralis part of the levatorani muscle.
The posterior surface is in front of the lower rectum. But the gland is separated from rectum by the rectovesical fascia (Denonvillier's fascia). The ejaculatory ducts pierce the posterior surface just below the bladder and pass obliquely through the gland for about 2 cm to open into the prostatic urethra about halfway down. Prostate's own ducts also open into this part of the urethra.
Capsule of the prostate gland
The prostate gland has true capsule and false capsule. The true capsule is formed by a strong layer of connective tissue at the periphery of the gland. The false capsule is formed by a condensation of pelvic fascia outside the true capsule. Prostatic plexus of veins lies between these two capsules.
Histology of prostatic gland
The gland consist of fibromuscular part and acini. Acini are varying in shapes and size. They are embedded in fibromuscular stroma. Fibromuscular part is formed by a mixture of connective tissue and smooth muscle. It is the characteristic histological feature of the prostatic gland.
The prostate gland is divided into zones and lobes. The lobes are classified as followings,
- Anterior lobe
- Lateral lobes (right & left)
- Posterior lobe
- Median lobe
The prostate gland consists 3 zones,
- Central zone (20%)
- Peripheral zone (70%)
- Transitional zone (5%)
They occupy the glandular substance approximately 20%, 70% and 5% respectively.
It is wedge in shape and forms the base of the prostate gland. Its apex is at the verumontanum. It surrounds the ejaculatory ducts.
It surrounds the central zone from behind and below. But it does not reach up to the base. It extends downwards to form the lower part of the gland.
It is situated around the distal part of the preprostatic urethra, just proximal to the apex of the central zone. The ducts of the transitional zone open on the verumontanum, just above where the ducts of the peripheral zone open into the prostatic sinuses.
Blood supply of the prostate gland
Arterial supply is mainly given by the prostatic branch of the inferior vesical artery. It is accompanied by following arteries,
- Small branches from middle rectal arteries.
- Internal pudental vessels
The veins run into the plexus between the true and false capsule of the prostate gland. This joins the vesicoprostatic plexus which is situated at the groove between bladder and prostate gland. This plexus also receives the deep dorsal vein of the penis. It drains backwards into the internal iliac veins.
The acini are controlled by the parasympathetic (cholinergic) innervation from the pelvic splenchnic nerves via inferior hypogastric plexus. The muscle fibres of the stroma are controlled by sympathetic (adrenergic) innervation from the inferior hypogastric plexus. The muscle fibres contract to empty the gland during ejaculation.
The lymphatics from prostate gland run across the pelvic floor mainly to the internal iliac nodes, a few may reach external iliac nodes.
The prostatic acini of the peripheral and transitional zones are formed from lateral epithelial buds which are formed from the pelvic part of the endodermal urogenital sinus. At this level the dorsal outgrowth of entry of the mesonephric ducts form the acini of the central zone. The fibromuscular stroma develops from the surrounding mesenchyme.
Benign prostatic hyperplasia
The benign prostatic hyperplasia usually affects the transitional zone. It compresses the peripheral zone while increasing in size. It is called as benign as it does not spread. The enlargement of the gland is called as hyperplasia.
Carcinoma of the prostate
The peripheral zone is the exclusive site of origin of carcinoma of prostate.
Note - The central zone rarely involve in any disease process.
Surgical approach of prostate gland
Now most operations for benign prostatic hyperplasia are carried out by the transurethral route with resectoscope. To avoid the damage of the external urethral sphincter the resection is done above the level of the verumontanum. Because the external urethral sphincter is distal to the verumontanum of the prostatic urethra.
An approach through an abdominal suprapubic incision into the retropubic space gibes exposure for a total removal of the organ for prostatic carcinoma.
- Total removal of prostate gland also can be done by laparoscopically or through a perineal approach.
- In this process the bladder neck is anastomosed to the membranous urethra.