Inguinal Canal: Anatomy and Hernias

The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. The canal contains the spermatic cord in men and the round ligament in women. An inguinal hernia occurs when tissue or an organ (such as a portion of the intestine) protrudes through in the abdominal wall and into the inguinal canal. Inguinal hernias are the most common type of hernia, and may be classified as indirect (tissue protrudes through the deep inguinal ring) or direct (tissue protrudes through the posterior wall of the inguinal canal). A hernia may cause pain or discomfort, and there is a risk of bowel obstruction due to bowel incarceration with possible strangulation and infarction. Surgery is indicated for inguinal hernias which are high-risk or cause significant pain.

Overview

• The 
  inguinal region
  , or the 
  groin
  , is located in the RLQ and LLQ of the anterior 
  abdominal wall
  .
• Boundaries:
  • Thigh
     inferiorly
  • Pubic tubercle medially
  • Anterior superior iliac spine
     laterally
• The inguinal canal runs in a straight line from the 
  anterior superior iliac spine
   to the pubic tubercle.
• Contents of inguinal canal:
  • Men:
    • Spermatic cord
       (with genitofemoral nerve)
    • Ilioinguinal nerve
  • Women:
    • Round ligament
    • Genitofemoral nerve
    • Ilioinguinal nerve
• Hesselbach triangle:
• A triangle of the 
  abdominal wall
• Located medial to the epigastric vessels
• Site of direct inguinal hernias

Embryologic Development

Formation of the inguinal canal

• Independent of testicular descent, in the 12th week of gestation, the anterior 
  abdominal wall
   musculature and 
  fascia
   form an evagination on each side of the midline known as the processus vaginalis.
• The processus vaginalis, in combination with the muscle and 
  fascia
   of the anterior 
  abdominal wall
  , forms the inguinal canal.
• In women, the ovum descends into the 
  pelvis
  , and the 
  round ligament
   of the 
  uterus
   travels through the inguinal canal to the 
  labia majora
  .

Male inguinal canal development

• The 
  testes
   originally reside in the posterior aspect of the abdominal cavity.
• Between 28 and 33 weeks' gestation, the 
  testes
   pass through the 
  inguinal region
   and into the 
  scrotum
  .
  • The 
    gubernaculum
    , 
    a band
     of mesenchymal tissue that terminates in the 
    inguinal region
     on the caudal pole of the 
    testes
    , assists the 
    testes
     in their migration.
  • Failed testicular descent results in 
    cryptorchidism
    .
• Descent of the 
  testes
   creates a weakness in the 
  abdominal wall
   in the region of the inguinal canal, making men particularly susceptible to 
  hernia
   formation.
• The connection between the processus vaginalis and the 
  peritoneum
   will obliterate at birth, but a serous sac will remain around the 
  testes
  , known as the 
  tunica vaginalis
   testis.
• Abdominal wall
   contributions:
  • Transversalis 
    fascia
     forms the internal spermatic 
    fascia
    .
  • Internal oblique
     muscle forms the cremasteric 
    fascia
     and muscle.
  • External oblique
     muscle forms the external spermatic 
    fascia
    .

Inguinal Canal Anatomy

Anterior 

abdominal wall

• The anterior 
  abdominal wall
   is composed of several muscles:
  • Rectus abdominis
  • External oblique
  • Internal oblique
  • Transversus abdominis
• The inner transversalis 
  fascia
   continues into the inguinal canal, forming the internal spermatic 
  fascia
  .

Course of the inguinal canal

• Approximately 4 cm long from 
  anterior superior iliac spine
   to pubic tubercle (superolaterally to inferomedially)
• Deep inguinal ring: an evagination of the transversalis 
  fascia
   (surrounding the 
  spermatic cord
   as the internal spermatic 
  fascia
  )
• Superficial inguinal ring: a 
  fissure
   in the aponeurosis of the 
  external oblique
   muscle

Boundaries of the inguinal canal

The boundaries of the inguinal canal vary throughout its course.

• At the level of the deep ring:
  • Anterior wall:
    • Internal oblique
       muscle
    • External oblique
       muscle
  • Posterior wall: transversalis 
    fascia
  • Roof: transversalis 
    fascia
  • Floor: 
    inguinal ligament
• At the middle of the inguinal canal:
  • Anterior wall: 
    external oblique
     aponeurosis
  • Posterior wall: transversalis 
    fascia
  • Roof: arching fibers of the 
    internal oblique
     muscle and 
    transversus abdominis
  • Floor: 
    inguinal ligament
• At the level of the superficial ring:
  • Anterior wall: 
    external oblique
     aponeurosis
  • Posterior wall: conjoint tendon
  • Roof: medial crus of 
    external oblique
     muscle
  • Floor: lacunar ligament

Borders of the Hesselbach triangle

• Refers to a triangle of the anterior 
  abdominal wall
• Boundaries:
  • Medial: lateral margin of the 
    rectus abdominis
     (linea semilunaris)
  • Superolateral: inferior epigastric vessels
  • Inferior: inguinal and pectineal ligament
• Direct hernias occur within the triangle, and indirect hernias occur lateral to the triangle.

Epidemiology and Etiology of Inguinal Hernias

Epidemiology

• Most common type of 
  hernia
   (> 75% of cases)
• Indirect inguinal hernias > direct inguinal hernias
• Ages of peak 
  incidence
  :
  • 0‒5 years of age
  • 75‒80 years of age
• Lifetime risk of approximately 25% for men and < 5% for women

Risk factors

• History of 
  hernia
   or previous 
  hernia
   repair
• Male 
  sex
• Older age
• Chronic obstructive 
  pulmonary disease
   (
  COPD
  )
• Chronic 
  constipation
• Weight lifting 
• Obesity
• Smoking

Etiology

• Congenital
  :
  • Due to abnormal development
  • Failed closure of the processus vaginalis
• Acquired:
  • Develop later in life due to progressive weakness of previously normal tissues
  • Conditions with increased intraabdominal pressure, such as strenuous physical activity, coughing, or 
    obesity
  • Sometimes 
    iatrogenic
     due to injury or abdominal surgery
• All direct hernias are acquired, while indirect ones may be 
  congenital
   or acquired.

Classification and Clinical Presentation

Classification

• Indirect hernias:
  • Lateral to the inferior epigastric blood vessels and the Hesselbach triangle 
  • Contents pass through the deep inguinal ring, traverse the entire trajectory of the inguinal canal, and exit the canal through the superficial inguinal ring.
  • Contents are encased by the coverings of the 
    spermatic cord
    .
• Direct hernias:
  • Medial to the inferior epigastric blood vessels and within the Hesselbach triangle
  • Contents protrude directly through the posterior wall of the inguinal canal and through the superficial inguinal ring, encased only by the external spermatic 
    fascia
    .
• Pantaloon 
  hernia
  : inguinal 
  hernia
   with both direct and indirect components
• Amyand 
  hernia
  : The 
  appendix
   is found within the 
  hernia
   sac.

Clinical presentation

• Mild inguinal 
  pain
   or discomfort
• Visible bulge in the 
  groin
   area, which increases upon standing or during physical activities that increase intraabdominal pressure (coughing, 
  sneezing
  , weight lifting) and reduces upon lying down.
• May be associated with a communicating 
  hydrocele
• Erythema
   may be noted over the 
  hernia
   if there is strangulation and tissue death.

Complications

• Incarceration:
  • Inability of the contents of the 
    hernia
     to return to their original cavity
  • Presents with severe 
    pain
     and a non-reducible bulge
  • If the intestines are incarcerated, symptoms of 
    intestinal obstruction
     develop.
• Strangulation:
• Contents of the 
  hernia
   must first become incarcerated.
• Blood supply to the incarcerated organs is compromised, which causes 
  ischemia
   and resultant tissue death.

Diagnosis and Management

Diagnosis

• Medical history and physical exam
• Palpation
   of the inguinal canal:
  • With the patient standing, palpate from the scrotal 
    skin
     toward the superficial inguinal ring.
  • Ask the patient to cough (
    Valsalva maneuver
    ).
  • Bulging can be felt at the fingertip.
• Imaging:
  • Used for confirmation in uncertain cases and occasionally surgical planning
  • Ultrasound :
    • Best initial imaging study in 
      patients
       without physical evidence of a 
      hernia
       
    • The diagnostic finding is an increased diameter of the inguinal canal (normally < 13 mm at the deep inguinal ring).
  • CT scans: particularly useful to distinguish between different subtypes of inguinal hernias
  • MRI:
    • Best imaging modality to differentiate between inguinal and femoral hernias with a 
      sensitivity and specificity
       greater than 95%
    • Due to the cost and limited availability of MRIs, CT scans are still more frequently used.

Management

• Surgical 
  hernia
   repair:
  • Complicated hernias
  • Uncomplicated hernias with moderate symptoms 
  • Selectively for uncomplicated hernias with mild 
    symptomatology
     or high risk of incarceration
  • Specifics of surgical repair techniques can be found in abdominal hernias.
• Surgical techniques:
  • Reinforcing the posterior wall of the inguinal canal with synthetic mesh
  • Reduction in the diameters of the inguinal rings