Male pelvic contents and the anal triangle

• Vas deferens

  •Muscular tube

  •Inguinal canal – spermatic cord

  •Join duct from seminal vesicle to form ejaculatory duct

  •Into prostate to meet urethra

  
• Vas deferens

  The vas deferens is a smooth muscle tube that transports sperm from the testis to the ejaculatory duct and so into the urethra. It passes in the spermatic cord through the superficial inguinal ring, along the inguinal canal and through the deep inguinal ring into the pelvis. It crosses the lateral wall of the pelvis to descend towards the seminal vesicles at the posterior surface of the bladder. It joins with the duct from the seminal vesicle to form the ejaculatory duct within the prostate gland.

  
• Vas deferens

  Sperm passes along the vas deferens and then receives fluid from the seminal vesicle and prostate gland to make the ejaculate more fluid as it passes into the urethra. It will also receive secretions from the bulbourethral glands in the deep perineal pouch.

  
• There are two smooth muscle tubes passing towards the bladder on each side in a male – a ureter and the vas deferens. They are of a similar size and can be mistaken for each other. The ureter passes into the pelvis from the abdomen and crosses the bifurcation of the common iliac vessels before descending towards the base of the bladder. The vas deferens crosses the lateral wall of the pelvis over the external iliac vessels to descend towards the seminal vesicles.

  
• Seminal vesicles

  •@5cm long – but uncoiled 10-15cm

  •Secrete liquid component of semen, fructose

  
• Seminal vesicles

  The seminal vesicles are highly coiled tubes that lie posterior to the bladder in males. They appear to be small, lumpy structures from an initial inspection but are actually a small bundle of a long tube similar to the vas deferens but coiled around itself and held together, wrapped in connective tissue. They secrete fluid to increase the liquid component of semen and also support the sperm – for example they release fructose which acts as a source of energy for the sperm.

  
• The distal end of the vas deferens and the seminal vesicles are supplied by branches of the anterior division of the internal iliac artery – the inferior vesical and prostatic arteries (this is a branch of the inferior vesical artery). The inferior vesical arteries also supply the bladder and distal part of the ureters in a male.

  
• The vas deferens (and arterial supply) can be seen passing towards the seminal vesicle. The pale pink structure anterior to the seminal vesicle is the prostate gland.

  
• Prostate gland

  •Inferior to bladder

  •Proteolytic enzymes and acid phophatase

  •Urethra and ejaculatory duct

  •Internal pudendal, middle rectal and inferior vesical arteries

  •Veins – deep dorsal of penis – plexus – internal iliac

  
• Prostate gland

  The prostate gland sits between the bladder and the pelvic floor. It is a small, walnut-sized structure in a young, healthy male. It also releases fluid that increases the liquid component of semen and helps to support the sperm. The fluid is alkaline and helps to neutralise the acid environment of the vagina. The prostate gland receives the ejaculatory ducts and has the urethra passing through it, it is usually described as being formed of 5 incompletely divided lobes.

  
• Prostate gland

  It is surrounded by a capsule of connective tissue that contains a venous plexus that drains blood towards the internal iliac veins. The prostatic venous plexus also has many communications with the vertebral veins – permitting metastasis of prostatic carcinoma to the lower vertebral column.

  
• The prostate gland is supported by the puboprostatic ligament and also the muscles of the pelvic floor. Pubococcygeus (part of levator ani) forms a muscular support for the prostate gland called puboprostaticus or levatore prostatae.

  
• Prostatic enlargement

  •May affect all, or part of the prostate

  •May be benign or malignant

  •Commonly seen in the DR (males aged 50+)

  
• Prostatic enlargement

  Benign enlargement of the prostate gland is common in males over 50 years of age. Benign enlargement affects all of the prostate but other changes may alter part of the prostatic lobes – a simple way to examine this is by using a rectal examination to detect alterations in the characteristic right and left lateral lobes separated by a groove that forms the posterior part of the prostate gland. Any enlargement of the prostate may affect the urethra and passage of urine from the bladder.

  
• Prostatic enlargement

  The slide shows enlargement of the median lobe of the prostate gland that has disrupted the smooth muscle sphincter at the base of the bladder. This causes leakage of urine and the desire to urinate. If the lobes increase in size the urethra may be compressed or distorted causing difficulties in releasing urine. This can form small pouches in the bladder, in which urine sits – increasing the chances of urinary infections.

  
• Lymphatic drainage

  Much of the lymph from the lower parts of the bladder, seminal vesicles, prostate gland and erectile tissues of the penis passes to lymph nodes clustered around the internal iliac artery. More distal parts of the penis will drain lymph to deep inguinal nodes. It is important to remember that lymph from the testis follows its arterial supply back to aortic nodes clustered around the root of the testicular artery.

  
• The median view shows the relationship between the pubic symphysis (Sy), urinary bladder (UB), prostate gland (P), seminal vesicle (SG) and rectum (R).

  The coronal image shows the bladder sitting immediately superior to the prostate gland. Immediately inferior to the prostate gland is the pelvic floor and then the bulb of the penis (B).

  
• The coronal MRI shows the highly coiled nature of the inside of the seminal vesicles (SG). At this coronal sectional level through the body, the structure posterior to the seminal vesicles can be seen appearing above and below the seminal vesicles – the rectum (R).

  The transverse MRI image shows the crura (Cr) – erectile tissues that form the corpora cavernosa of the penis and the urethra (U) in the bulb of the penis. Posterior to this is the anal canal (A). Either side of the anal canal is a fat-filled space called the ischioanal fossa (IAF) part of the anal triangle.

  
• Anal triangle

  The anal triangle describes an area found in males and females. It is delineated by an imaginary line between the ischial tuberosities (the base of the triangle) and the coccyx (the apex of the triangle). The rectum becomes the anal canal as it pierces the pelvic floor in the anal triangle. The spaces either side of the rectum are called the ischiorectal (or ischioanal) fossae.

  
• Ischioanal (rectal) fossa

  •Walls = ischial tuberosity, rectum/anal canal

  •Roof = levator ani (pelvic diaphragm)

  •Floor = skin

  •Contents = branches of the pudendal nerve, artery, vein,  and adipose tissue

  
• Ischioanal (rectal) fossa

  The anal canal is surrounded by the external anal sphincter, which is supplied by a branch of the pudendal nerve – the inferior rectal nerve. The wall of the rectum and anal canal is supplied by the inferior rectal artery – a branch of the internal pudendal artery. The main component of this space is fat, this supports the neurovascular structures and allows the anal canal space into which it can expand during expulsion of faeces from the body.

  
• The perineal nerve (a branch of the pudendal nerve) passing close to the ischial tuberosity accompanied by the internal pudendal artery. The inferior rectal vessels and nerves cross the ischioanal fossa towards the external anal sphincter.

  
• Anal canal

  The anal canal is the final part of the digestive tract. It has small internal folds called anal columns that contain tiny branches of the superior rectal vessels. The wall of the anal canal forms the involuntary internal anal sphincter and voluntary control of defaecation is from the skeletal muscle that surrounds the opening of the anal canal – the external anal sphincter.

  
• External anal sphincter

  •Skeletal muscle

  •Perineal body to anococcygeal ligament

  •Closes anus (rectal control aided by puborectalis)

  •Pudendal nerve (S2-4) inferior rectal branch

  
• External anal sphincter

  The external anal sphincter wraps around the opening of the anal canal by passing between the anococcygeal ligament and the perineal body. The perineal body is a small, dense structure composed of connective tissue that lies at the edge of the urogenital diaphragm to provide attachment to muscles of the perineum in addition to the external anal sphincter. The external anal sphincter controls the release of faeces from the body.

  
• External anal sphincter

  The internal sphincter will open as the rectum fills, so it is the external sphincter that is under voluntary control (via the pudendal nerve). Puborectalis (part of the pelvic floor muscles) aids the external anal sphincter by bending the rectum to slow the passage of faeces and help maintain continence.

  
• The wall of the anal canal and surrounding structures forms a complex communication between smooth muscle, connective tissue and skeletal muscle. The external sphincter is divided into deep, superficial and subcutaneous parts by connective tissue and the inferior rectal vein forms an internal venous rectal plexus superficial to the internal sphincter.

  
• The slide shows two other features of the anal canal – the pectinate and white lines. The pectinate line at the base of the anal columns is an important landmark for the end of the visceral (internal) part of the digestive tract and the start of the parietal (body wall) structures.

  ‘Levator ani’ on this slide represents puborectalis as it blends with the wall of the rectum to help control continence.

  
• Arterial Supply

  The wall of the rectum is supplied by superior rectal (from inferior mesenteric), middle rectal (from internal iliac) and inferior rectal (from internal pudendal) arteries. The inferior rectal arteries supply the wall of the anal canal but the end of the superior rectal arteries lie within the anal columns on the internal surface of the canal.

  
• Veins and Lymph

  the change in innervation, vascular pattern and lymphatic drainage at the pectinate line.