Pelvis & Perineum Anatomy

Learning Outcomes

• After this lecture, students should be equipped to describe the anatomy of the bony pelvis along with explaining the contrast between male and female features.
• Students should be able to describe the surface anatomy and innervation of the perineum.
• Students should be able to describe the peritoneal reflections and recesses within the perineum.
• Students should be able to demonstrate an understanding of the anatomy surrounding the inguinal hernias along with their clinical findings and the mechanism for how they develop.
• Students should be able to describe the layers of the scrotum, the testis and epididymis along with describing the effects of torsion.

Urinary System

• Ureters have 3 areas of constriction:
• The junction of the ureters and renal pelves (ureteropelvic junction).
• Where the ureters cross the brim of the pelvic inlet.
• During the passage through the wall of the urinary bladder (Uterovesical junction).
• The blood supply to the ureter is derived from:
• Branches from the renal artery
• Branches from the gonadal artery
• Branches from the common iliac arteries
• Branches from the internal iliac arteries
• Branches from the aorta
• The abdominal part of the ureters derive their nerve supply from:
• The renal plexuses
• Abdominal aortic plexuses
• Superior hypogastric plexuses
• Visceral afferent fibers carry pain sensations along the sympathetic fibers retrograde to the spinal ganglia and cord segments T11-L5.
• Referred pain from the above is felt in the small of the back, lumbar region (flank) and genitals, this can be described as loin to groin pain.
• Structures from the most superficial to deep at the level of kidneys are:
• Renal Fascia
• Transversalis Fascia
• Paranephric Fat
• Renal Capsule
• Kidney
• Perinephric Fat

Anterior Abdominal Wall

• The arcuate line is a landmark on the posterior surface of the anterior abdominal wall.
• Relevant structures in this area are:
• Median umbilical ligament
• Medial umbilical fold
• Medial and Lateral umbilical ligaments
• Inferior epigastric artery
• Deep circumflex artery

Hernias

• Indirect inguinal hernias are more common in men and babies.
• This is due to a patent process vaginalis.
• The abdominal content passes through the deep ring and the bulge occurs lateral to the epigastric vessels.
• Direct inguinal hernias occurs through a weakened posterior wall therefore the abdominal content passes through.
• The bulge occurs medial to the epigastric vessels (Hesselbach’s triangle).
• Direct inguinal hernias are more common in mature men and are usually acquired from heavy lifting, constipation, or sports.

Descent of the Testis

• The gubernaculum guides the testes through the inguinal canal to the scrotum.
• The gonads follow the gubernaculum.
• The spermatic cord follows, now lying in the inguinal canal.
• Also, the gubernaculum degenerates.
• As the testis descends, the peritoneum evaginates to form the processus vaginalis.
• It follows the course of the gubernaculum.
• It is anterior to the gubernaculum and testes.
• Usually, it obliterates.
• If it does not it may lead to pathologies.
• A small part persists as the tunica vaginalis.

Testicular Torsion

• Testicular torsion (twisting) of the spermatic cord results in compression of the vasculature and can lead to infarction or complete gangrene of the testicle.
• Excessive mobility of the testis due to various developmental anomalies is a common predisposing factor.
• Torsion of the tiny vestigial appendix testis may cause acute pain in the scrotum, simulating acute epididymitis or mimicking acute appendicitis from a referred pain pattern.

Varicocele and Hydrocele

• A varicocele involves swollen veins in the scrotum.
• A hydrocele involves an accumulation of serous fluid.

Weakness in Pelvic Support

• Rectocele: Weakening of the tissue that lies between the vagina and rectum (rectovaginal fascia) that allows the rectum to protrude into the lower posterior vaginal wall.
• Cystocele: Occurs when there is descent in the anterior compartment, and the bladder prolapses into the vagina.
• Uterine prolapse: Uterus support (ligaments, perineal body, levator ani) weakens and the uterus drops into the vagina.

Injury to the Pelvic Floor

• During childbirth, the pelvic floor supports the fetal head while the cervix of the uterus is dilating to permit delivery of the fetus.
• The perineum, levator ani, and pelvic fascia may be injured during childbirth.
• This may alter the position of the neck of the bladder and urethra which may cause urinary stress incontinence.

Spermatic Cord

• The 3 layers of the spermatic cord are:
• Internal spermatic fascia (transversalis fascia).
• Cremasteric layer (internal oblique).
• External spermatic fascia (external oblique).
• The 3 arteries of the spermatic cord are:
• Testicular from the Aorta at L2.
• Cremesteric from the Inferior Epigastric.
• Artery of Vas from the Superior Vesical.
• The 3 nerves of the spermatic cord are:
• Nerve to cremaster, from the Genitofemoral nerve.
• Sympathetics which carry pain sensation.
• Ilioinguinal nerve.
• The 3 other things contained within the spermatic cord include:
• Vas deferens.
• Lymphatics to para-aortic nodes at L2
• Pampiniform plexus of veins.

Sacral Plexus

• Formed by the anterior rami of S1-4 and the lumbosacral trunk.
• Found anterior to the piriformis muscle.
• The main branches include: -Sciatic nerve (L4-S3). -Pudendal nerve (S2-4). -Superior (L4-S1) and inferior (L5-S2) gluteal nerves. -Posterior cutaneous nerve of the thigh (S1-S3). -Pelvic splanchnic nerves (S2-4) which carry preganglionic parasympathetic fibers as well as visceral afferents.

Autonomics of the Pelvis

• Autonomics enter the pelvic by 4 main routes:

1. Sacral sympathetic trunks which mainly supply the lower limb and carry postsynaptic fibers.
2. Per-arterial plexuses which supply the superior rectal, ovaries and internal iliac arteries.
3. Pelvic splanchnic carry parasympathetic innervation to the pelvic and hindgut.
4. Hypogastric plexuses which are the most important sympathetic route.

• Inferior hypogastric plexuses contain sympathetic fibers, parasympathetic fibers, and visceral afferents.
• The inferior hypogastric plexuses give origin to the rectal plexus, uterovaginal plexus, prostatic plexus, and vesical plexus.

Female Reproductive Organs

• The nerves of the ovaries and uterine tube descend via the ovarian plexus on top of arteries.
• Visceral afferents for pain travel back with sympathetic fibers to T11-L1.
• Visceral afferents for reflex travel back with parasympathetics to S2-S4.
• Nerves from the uterovaginal nerve plexus, supply the uterus and superior part of the vagina, carry both sympathetic fibers (T12-L2) and parasympathetic fibers (S2-4).
• The visceral afferents associated with the uterus and superior part of the vagina include:
• Visceral afferents carrying pain from intraperitoneal structures travel back with sympathetic nerves (uterine fundus and body) above the pain line.
• Visceral afferents carrying pain from sub-peritoneal structures follow parasympathetics (cervix and vagina-upper 3/4) below the pain line.
• The inferior quarter of the vagina is supplied by the somatic-pudendal nerves.
• Types of nerve blocks in this area:
• Pudendal block anesthetizes S2-4/somatic nerves.
• Caudal block anesthetizes S2-4 and somatic+parasympathetic nerves.
• Spinal block anesthetizes somatic+parasympathetic+sympathetic nerves.

Male Internal Genital Organs

• Nerves from the inferior hypogastric plexus in male internal genital organs carry sympathetic (T12-L2), parasympathetic (S2-4) and visceral afferent fibers.
• Sympathetic activity (T12-L2) causes: -Contraction of the internal urethral sphincter. -Stimulates rapid peristalsis of the ductus deferens. -Causes contraction and secretion of the prostate and seminal vesicles. -Ejaculation.
• Parasympathetic activity (S2-3) innervates the erectile tissue -Prostatic plexuses form the cavernous nerves that innervate the erectile tissue of the penis resulting in an erection.

Urethra Differences

• Males: -The long urethra bends twice. -1. The pre-prostatic urethra. Internal urethral sphincter. -2. Prostatic- where the prostatic sinus and seminal colliculus lie. -3. Membranous- which contains the External urethral sphincter. -4. Spongy- contains the Corpus spongiosum and openings of the bulbourethral glands. Two parts: bulbar and penile.
• Females: -Short tube. -Passes Through the pelvic floor and perineum before opening into the vestibule. -Consists of Para-urethral mucous glands.
• Features of prostatic urethra include: -Capsule. -Prostatic urethra containing the seminal colliculus. -Bulbourethral glands.

Ectopic Pregnancy

• An ectopic pregnancy happens when ablastocyst fails to reach the uterus and may implant in the mucosa of the uterine tube.
• Tubal rupture and severe hemorrhage pose a significant threat to the mother's life and will result in the embryo's demise.

Blood Supply to Female Reproductive Organs

• The ovaries and uterine tubes get their blood supply from the ovarian artery.
• The uterine artery anastomoses with branches from the ovarian and vaginal arteries.
• The vagina is supplied by the vaginal artery and internal pudendal artery.