What is the anatomy of an inguinal hernia?

Anatomy of Inguinal Hernia

An inguinal hernia results from incomplete involution of the processus vaginalis, creating a patent processus vaginalis (PPV) through which intra-abdominal structures like bowel can herniate into the inguinal canal. 1

Embryological Development

• Testicular descent involves two distinct phases: intra-abdominal and extra-abdominal 2
• During the intra-abdominal phase (8-15 weeks postconception), the testis migrates from the urogenital ridge as the craniosuspensory ligament regresses and the gubernaculum thickens 2
• The gubernaculum anchors the testis to the scrotum through the external and internal rings of the inguinal canal 2
• In females, the craniosuspensory ligament is maintained (keeping ovaries in retroperitoneal position) and the gubernaculum persists as the ovarian round ligament 2
• During the extra-abdominal phase (25-35 weeks gestation), the testis descends through the inguinal canal, drawing with it an extension of peritoneal lining called the processus vaginalis 2

Processus Vaginalis and Hernia Formation

• Normally, the processus vaginalis obliterates and involutes, forming the tunica vaginalis 2
• Incomplete involution results in a patent processus vaginalis (PPV) 2
• If the communication is large, intra-abdominal structures (typically bowel) can herniate through this defect, resulting in an indirect inguinal hernia 2
• The genitofemoral nerve innervation is critical for regulation of gubernacular length and obliteration of the processus vaginalis 2

Epidemiology and Distribution

• More than 90% of pediatric inguinal hernias occur in boys due to the relationship between processus vaginalis and testicular descent 2
• 60% of indirect inguinal hernias occur on the right side, consistent with the observation that involution of the left processus vaginalis precedes that of the right 2
• The prevalence of PPV is highest during infancy (up to 80% in term male infants) and declines with age 2
• Not all cases of PPV result in inguinal hernias; the estimated childhood risk of developing an inguinal hernia with a PPV is between 25% and 50% 2

Anatomical Structures of the Inguinal Region

• The inguinal canal contains important structures that play roles in hernia formation and repair 3:

  • Iliopubic tract - a key structure that lies in the plane of the original defect of most groin hernias 3
  • Transversus abdominis aponeurosis 4
  • Transversalis fascia 4
  • External oblique aponeurosis 5

• A physiologically dynamic and strong posterior inguinal wall, along with the shielding and compression action of surrounding muscles and aponeuroses are important factors that prevent hernia formation 5

• The posterior wall of the inguinal canal is often weak and without dynamic movement in patients with inguinal hernias 5

Clinical Implications

• Inguinal hernias should be repaired to avoid the risk of bowel incarceration and gonadal infarction/atrophy 1
• The physical features of hernia (size of abdominal wall defect, amount of herniating intestine, ease of reduction) do not consistently predict the risk of incarceration 1
• Delayed treatment (>24 hours) of strangulated hernias is associated with higher mortality rates 1

Diagnostic Considerations

• While inguinal hernias are easily diagnosed on physical examination in men, ultrasonography is often needed in women 6
• Magnetic resonance imaging has higher sensitivity and specificity than ultrasonography and is useful for diagnosing occult hernias if clinical suspicion is high despite negative ultrasound findings 6