Inguinal Canal and Spermatic Cord

Inguinal Canal and Spermatic Cord

Negative Feedback Loop

• The thermostat in a house exemplifies a negative feedback loop system.
• When the temperature decreases, the thermostat activates the furnace to release warm air until the target temperature is attained.
• The thermostat then detects this and shuts off the system until the temperature drops to the threshold again.
• A similar feedback mechanism is present in the tissues of the scrotum and spermatic cord to regulate testicle temperature.

Introduction to the Inguinal Canal and Spermatic Cord

• The inguinal canal is the inferior part of the anterolateral abdominal wall.
• It contains the same myofascial layers as the anterolateral abdominal wall, but they are specialized.
• The spermatic cord and testis are also examined, relating to the descent of the testis.
• The testis produces spermatozoa, which need to be below body temperature for normal development.
• During development, the testis descends outside the abdominal cavity into the scrotum.
• This descent creates an evagination through the anterolateral wall along the inguinal canal, modifying the myofascial elements to form the spermatic cord.

Objectives

• Examine the organization of the inguinal canal and how myofascial layers contribute to its structure.
• Analyze the spermatic cord structure, including a discussion of the male gonad.
• Discuss clinical conditions associated with this area.

Embryological Development

• Early in embryology, undifferentiated gonads develop along the posterior abdominal wall.
• A connective tissue tract, the gubernaculum, anchors the gonads to the anteroinferior abdomen.
• During fetal development, the gubernaculum retracts, pulling the gonad in an anteroinferior direction.
• This retraction is more pronounced in males, causing the testes to descend into the scrotum.
• Postnatally, the gubernaculum persists as the scrotal ligament in males.
• In females, the ovaries remain suspended in the posterior abdominal pelvic cavity, with minimal gubernaculum retraction.
• The gubernaculum degenerates to form the round ligament of the uterus, anchoring it to the labia majora.
• Both males and females have communication between the abdominal pelvic cavity and external genitalia.
• In males, it is the spermatic cord into the scrotum; in females, it is the round ligament into the labia majora.
• The inguinal canal is the channel of communication in both sexes.

Structure of the Inguinal Canal

• The inguinal canal is bound and reinforced by the myofascial layers of the anterolateral abdominal wall.
• The aponeurosis of the external oblique muscle forms the anterior wall of the inguinal canal.
• Inferiorly, the aponeurosis curves dorsally to form the floor of the inguinal canal.
• The inguinal ligament runs from the anterior superior iliac spine to the pubic tubercle, providing structural support.
• The medial-most point of the inguinal canal is at the pubic tubercle, where the terminal fibers form the superficial inguinal ring.
• The spermatic cord and round ligament exit the inguinal canal at this point.
• The posterior wall is formed by the aponeurosis of the internal oblique and transversalis fascia.
• These tendons are often fused as the conjoint tendon, a weak point prone to tears leading to direct inguinal hernias where abdominal contents bulge through.
• Medially, the conjoint tendon is anchored to the pubic crest and pectineal line.
• The lacunar ligament projects off the inguinal ligament to the conjoint tendon, supporting the medial floor.
• Laterally, fibers of the transversus abdominis arch over the spermatic cord or round ligament to form the deep inguinal ring, marking the lateral termination of the canal.
• Deep to the conjoint tendon, the transversalis fascia projects inferiorly to blend into the inguinal ligament, forming the ileopubic tract.
• This fusion creates a functional boundary between the abdomen and lower limb.

Scrotum and Spermatic Cord Layers

• The skin is continuous with the anterolateral abdominal wall.
• Camper's fascia thins to become almost imperceptible in the scrotum.
• Scarpa's fascia continues into the scrotum and is modified for thermal regulation.
• The scrotum needs to maintain a temperature below body temperature to prevent frostbite.
• Scarpa's fascia transitions into dartos fascia, a thin latticework of smooth muscle fibers.
• When the temperature drops, the dartos fascia contracts, condensing like shrink-wrap, which:
  • Decreases surface area for heat radiation.
  • Thickens the scrotum wall, forming an insulation barrier.
  • Draws the testicle closer to the abdominal pelvic cavity to absorb heat.
  • Generates a small amount of heat through muscle contraction.
• Dartos fascia also contracts during sexual arousal, aiding in fluid propulsion during ejaculation.
• A fascia layer from the external oblique muscle joins the spermatic cord as the external spermatic fascia.
• The internal oblique muscle forms the cremasteric fascia, containing muscle fibers that contract to elevate the testicle for thermoregulation and sexual arousal.
• The cremasteric reflex involves the cremaster muscle contracting to lift the testicle when the inner thigh is stroked, protecting against potential harm and testing the lower spinal cord integrity.
• The transversus abdominis does not contribute to the spermatic cord.
• The transversalis fascia continues into the cord as the internal spermatic fascia.
• The parietal peritoneum forms the processus vaginalis, leading the testicle through the inguinal canal.
• Postnatally, the processus vaginalis fuses to seal off the passage, but incomplete fusion can lead to indirect inguinal hernias where abdominal contents enter the scrotum.

Spermatic Cord Structures

• Neurovascular Structures:
  • The testicular artery branches off the descending aorta and enters the inguinal canal through the deep inguinal ring to supply the testicle.
  • Testicular veins form the pampiniform plexus, a series of parallel vessels surrounding the artery for temperature regulation.
  • The pampiniform plexus creates a countercurrent arrangement for heat exchange, cooling arterial blood before it reaches the testicle.
• Nerves:
  • The ilioinguinal nerve penetrates the internal oblique aponeurosis and accompanies the spermatic cord, providing cutaneous sensation to the anterior external genitalia and supramedial thigh.
  • The genital branch of the genitofemoral nerve is the principal motor nerve for the cremaster and dartos muscles. It enters the inguinal canal through the deep inguinal ring.
• Ductus Deferens (Vas Deferens):
  • It is a thick muscular tube with a small lumen, identifiable by its rigidity.
  • It is nourished by the testicular artery off the internal iliac artery and has a rich sympathetic nerve supply for peristaltic contractions during ejaculation.

Testicle Structure

• The testicle is an ovoid organ for spermatozoa production, descending through the inguinal canal via the processus vaginalis.
• The processus vaginalis opens as the tunica vaginalis, with a parietal layer lining the scrotum and a visceral layer covering the testicle.
• The tunica albuginea, a thick fibrous connective tissue, forms the outer cortex, dividing the testicle into lobules.
• Within the lobules, seminiferous tubules produce spermatozoa, converging to form the rete testes.
• Spermatozoa then pass into the epididymis for storage and maturation.
• The epididymis tapers posteriorly, becoming the vas deferens.