Pelvic Anatomy and Ureters

Learning Outcomes

• By the end of this lecture, the anatomy of the bony pelvis, including the contrast between male and female features, should be understood.
• The surface anatomy and innervation of the perineum should be known.
• Understanding of the peritoneal reflections and recesses within the perineum is important.
• An understanding of how inguinal hernias develop, including their anatomy and clinical findings, is important.
• Should be able to describe the layers of the scrotum, the testis and epididymis, and the effects of torsion.

Ureter

• Constriction areas are located at the junction of the ureters and renal pelves (ureteropelvic junction), where the ureters cross the brim of the pelvic inlet, and during their passage through the wall of the urinary bladder (Uterovesical junction).
• The blood supply to the ureter comes from branches of the renal, gonadal, common iliacs, and internal iliacs arteries, as well as branches from the aorta.
• The nerves to the abdominal part of the ureters derive from renal, abdominal aortic, and superior hypogastric plexuses.
• Visceral afferent fibers convey pain sensations retrograde to spinal ganglia and cord segments T11-L5.
• Referred pain may be felt in the small of the back, lumbar region (flank), and genitals, manifesting as loin to groin pain.

Anterior Abdominal Wall

• The arcuate line is a significant landmark on the posterior surface.
• The median umbilical ligament and medial umbilical ligament are key structures.
• The inferior epigastric artery and deep circumflex artery are important vascular components.
• The medial umbilical fold and lateral umbilical fold are also present on the posterior surface.

Hernias

• Indirect inguinal hernias are more common in men and babies and can be caused by a patent process vaginalis.
• In indirect inguinal hernias, the abdominal content passes through the deep ring, causing the bulge to occur lateral to the epigastric vessels.
• Direct inguinal hernias the abdominal content passes through a weakened posterior wall, causing the bulge to occur medial to the epigastric vessels which forms Hesselbach’s triangle.
• Direct inguinal hernias are more common in mature men and are often acquired through heavy lifting, constipation, or sports.

Descent of Testis

• Gubernaculum guides the testes through the inguinal canal to the scrotum.
• The gonads follow the gubernaculum.
• The spermatic cord also follows, and the gubernaculum degenerates after the descent is complete.
• Processus vaginalis, an evagination of the peritoneum, follows the course of the gubernaculum.
• It is anterior to both the gubernaculum and testes and usually obliterates, but a small part may persist as the tunica vaginalis.

Testicular Torsion

• Torsion, or twisting of the spermatic cord, results in compression of the vasculature.
• The most common predisposing factor is excessive mobility of the testis due to developmental anomalies.
• Torsion of the tiny vestigial appendix testis may cause acute pain in the scrotum, simulating acute epididymitis or mimicking acute appendicitis that manifests as referred pain.

Weakness in Pelvic Support

• Rectocele: Weakening of the tissue between the vagina and rectum (rectovaginal fascia) allows the rectum to protrude into the lower posterior vaginal wall.
• Cystocele: Descent in the anterior compartment causes the bladder to prolapse into the vagina.
• Uterine prolapse: Weakening of the uterus support (ligaments, perineal body, levator ani) causes the uterus to drop into the vagina.

Injury to Pelvic Floor

• The pelvic floor supports the fetal head during childbirth.
• The perineum, levator ani, and pelvic fascia may be injured during childbirth.
• These injuries may alter the position of the neck of the bladder and urethra and cause urinary stress incontinence.

Spermatic Cord

• Consists of three layers: internal spermatic fascia, cremasteric layer, and external spermatic fascia.
• It contains three arteries: testicular, cremasteric, and artery of vas.
• It consists of three nerves: nerve to cremaster, sympathetic, and ilioinguinal.
• Contains the vas deferens and pampiniform plexus of veins, with lymphatics to para-aortic nodes at L2.

Sacral Plexus

• Formed by the anterior rami of S1-4 and the lumbosacral trunk.
• Located anterior to the piriformis muscle.
• Consists of several main branches which include: sciatic nerve (L4-S3).
• Other nerves include: Pudendal nerve (S2-4)
• Superior (L4-S1) and inferior (L5-S2) gluteal nerves, posterior cutaneous nerve of the thigh (S1-S3), and pelvic splanchnic nerves (S2-4), including preganglionic parasympathetic and visceral afferents.

Autonomics of Pelvis

• The autonomic nerves enter the pelvic by four main routes.
• Sacral sympathetic trunks mainly supply the lower limb and postsynaptic fibers.
• Peri-arterial plexuses supply the superior rectal, ovaries, and internal iliac arteries.
• Pelvic splanchnic nerves provide parasympathetic innervation to the pelvic and hindgut.
• The hypogastric plexuses are the most important sympathetic route.

Hypogastric Plexus

• The inferior hypogastric plexus contains sympathetic, parasympathetic, and visceral afferent fibers.
• Arises from the rectal, uterovaginal, prostatic, and vesical plexuses.

Female Reproductive Organs

• The ovaries and uterine tube receive innervation.
• Nerves descend via the ovarian plexus on top of arteries.
• Visceral afferents carry pain via sympathetic fibers to T11-L1 and reflexes via parasympathetics to S2-S4.
• The uterus and superior part of the vagina.
• Nerves from the uterovaginal nerve plexus carry sympathetic (T12-L2), parasympathetics (S2-4), and visceral afferents.
• Visceral afferents carrying pain from intraperitoneal structures go back with sympathetic fibers.
• The inferior quarter of the vagina is innervated by somatic-pudendal nerves.

Regional Blocks

• Pudendal block anesthetizes the S2-4 region and is somatic.
• A caudal block anesthetizes S2-4 and is both somatic and parasympathetic.
• Spinal block anesthetizes the somatic, parasympathetic, and sympathetic areas

Male Internal Genital Organs

• The nerves from the inferior hypogastric plexus carry sympathetic (T12-L2), parasympathetic (S2-4), and visceral afferent fibers.
• Sympathetic innervation (T12-L2) causes contraction of the internal urethral sphincter, stimulates rapid peristalsis of the ductus deferens, and contributes to contraction and secretion of the prostate and seminal vesicles, resulting in ejaculation.
• Parasympathetic innervation (S2-3) supplies the erectile tissue.
• Causes the prostatic plexuses to form cavernous nerves which innervate the erectile tissue of the penis and are responsible for erection.

Male and Female Urethra

• Males urethra is both long and bends twice.
• The male urethra has four regions: pre-prostatic, prostatic, membranous, and spongy.
• The membranous portion contains the external urethral sphincter.
• The spongy portion contains the corpus spongiosum and bulbourethral glands, with two parts: bulbar and penile.
• The female urethra is short and goes through the pelvic floor and perineum to open into the vestibule, and has para-urethral mucous glands.

Male Urethra

• The prostatic urethra contains the prostatic urethra, seminal colliculus. Has multiple openings
• The bulbourethral glands are also present.

Female Reproductive Organs

• Ectopic pregnancy happens when a blastocyst implants in the uterine tube which causes tubal rupture and severe hemorrhage that can be life-threatening.
• The ovarian artery supplies the ovary and uterine tubes, while the uterine artery anastomoses with branches from the ovarian and vaginal arteries.
• The vagina is supplied by the vaginal artery and internal pudendal artery.