Hernia

• A hernia is defined as the displacement of the small intestine through a normal or pathologic foramina.
  • Occasionally, the large intestine is involved.

Pathogenesis

Diagram of a hernial sac (Courtesy of Elspeth Milne)

• Associated with trauma or the weakening of tissues.
  • For example,
    • Old age
    • Pregnancy
    • Straining
    • Wound dehiscence.
• Most hernias are external
  • Contents pass through a hernial ring in the abdominal wall.
  • Are covered with parietal peritoneum, soft tissue and skin.
    • A hernial sac.

Sequelae

• The sequelae depend on whether the hernia is reducible, or is an incarceration.

Reducible hernia

• The hernial contents are freely moveable.
• There are NO sequelae.

Incarceration

• The small intestine contents are trapped.
  • The hernia is non-reducible.
• Venous drainage is obstruced.
  • Oedema
  • Congestion
• Adhesions form between the contents and the sac.
• Accumulated gas/ ingesta distends the herniated viscus.
• Obstruction of lumen leads to
  • Rupture
  • Peritonitis
  • Death.

Types of hernia

• Umbilical - usually congenital.
• Diaphragmatic - common following road traffic accidents in the dog and cat.
• Inguinal/scrotal - may be:
  • Congenital
  • Acquired
    • E.g. post castration of stallion
• Perineal - old male dogs with prostate enlargement.
• Ventral -wound site breakdown, old mares
• Omental/mesenteric - internal hernias.

Volvulus (Courtesy of Bristol BioMed Image Archive)