Definition

The abnormal protrusion of a cavities contents through a weakness in the cavity wall, that involves all layers.

That be divided into congenital and acquired and as:

• Internal
  • Diaphragmatic hernia - congenital or acquired
  • Duodenum herniating in the paraduodenal pouch
  • Intestine into the lesser sac
  • Into a hole in mesentery (following previous surgery, e.g. right hemi)
  • Into a hole in transverse mesocolon
  • Into defect in broad ligament
  • Into Ileo-caecal fossae - superior & inferior
  • Into retro-caecal fossa
  • Into a pocket created by a band adhesion

• External
  • Anterior
    • Inguinal - indirect & direct
    • Femoral
    • Umbilical - Exomphalos (major & minor), & child umbilical hernia.
    • Paraumbilical
    • Epigastric
    • Divarication of Rectii - put here as a note, not really a hernia (although some would argue that is does fit the def. However, you never repair)
    • Spigelian
    • Obturator
    • Interstitial / Interparietal - 4 types -
      • Pro-peritoneal - diverticulum from inguinal or femoral hernia.
      • Intermuscular - common in obese patients - spreads between EO & IO - narrow neck - tendency to strangulation.
      • Inguinosuperficial - hernia into the superficial inguinal pouch - associated commonly with an ectopic testis in the pouch.
      • Spigelian - occurs at lateral border of rectus sheath at level of arcuate line.
  • Posterior
    • Lumbar - superior & inferior. May be a phantom hernia - d.t. local muscular paralysis e.g. polio.
    • Gluteal - through greater sciatic foramen.
    • Sciatic - through lesser sciatic foramen.
  • Perineal hernia - 4 types
    • Post - operative - after AP resection of rectum.
    • Median sliding hernia - complete rectal prolapse.
    • Antero-lateral - in females - swelling of one side labium majus.
    • Postero-lateral - through levator ani muscle into the ischirectal fossa.
  • Para stomal hernia
    • Para-ileostomy
    • Para-colostomy

Aetiology

There would appear to be many factors that contribute to hernia formation. And there are a number of eponymous theories, they are here for interest sake.

• Russell's theory - Mr Hamilton Russel (1906) suggested that all hernia are congential and so form in pre-existing sacs - NOT TRUE
• Cloquet's lipoma theory - (1817) Cloquet's lipoma is a spermatic cord lipoma. It's presence alone can be mistaken for a hernia. It was postulated that it's presence induced a wekaness and cold led to true hernia formation
• Fruchaud's theory - big opening in the lower abdomen - between the pubic bone and conjoint tendon. Divided into two by inguinal ligament. Through the upper part passes the inguinal hernia, while through the lower part passes the femoral hernia.
• Denervation theory - division of the ilioinguinal nerve esp after appendectomy.
• Uglavasky theory - chronic increased intra-abdominal pressure
• Peacock's theory - defective collagen synthesis.
• Walk's theory - weakness of abdominal wall at exit of neurovascular bundle.
• Keith's theory - stress related degeneration of connective tissue - especially in the fascia transversalis.
• Deficient insertion of the conjoint tendon seen in males - especially white males - pre-disposes to direct inguinal hernia - less support to posterior inguinal canal wall. Attachment quite wide in females - direct hernia almost never occurs in females.

Collagen related factors

• Hernias are more common in patients with connective tissue disorders e.g. Ehlers-Danlos (NB there are over 10 types, mainly effects Type I and III collagen)
  • Type I the most abundant type. Tendons, skin, arterial wall and scar tissue. Closely associated with type III
  • Type II mainly cartilage (hyaline), vitreous humour of eye
  • Type III produced by fibroblasts before stronger type I is made.
  • Type IV basement membrane
  • Type V associated with type I, hair, interstitial tissue and placenta
  • There are many other type going all the way to XXIX!
• Key experimental finding is that a reduced type I to III ratio leads to increased hernia prevalence