Category:Intestine - Physical Disturbances

Category:Obstruction, Intestinal

Positional Changes/ Displacements

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

• Associated with trauma or the weakening of tissues.
  • For example,
    • Old age
    • Pregnancy
    • Straining
    • Wound dehiscence.
• Most hernias are external
  

  Diagram of a hernial sac (Courtesy of Elspeth Milne)
  • 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)

Volvulus

• A twist about the long axis of the gut.
• Generally in the small intestine.
• Intense congestion
  • Often almost black.
• Mostly in young animals
  • Especially calves and piglets
  • Occasionally sheep and dogs.
  • Occasionally in greater mesentery of horse.

Pathogenesis

• Loop of bowel twists through 180 degrees around mesentery to produce obstruction of lumen.
• Proximal the the obstruction, the bowel becomes rapidly distended.
  • Venous return is first shut off, but the arterial supply remains.
    • Bowel becomes engorged with blood.
  • Produces rapid death.
• Bowel becomes hypoxic.
  

  Torsion of the large colon in the horse (Courtesy of Elspeth Milne)
  • Toxic material and bacteria pass through the anoxic wall of bowel.
• In piglets may see whole of small intestine twisted around root of mesentery.
  • Very little can be done to resolve this** Produces rapid death

Torsion

• A twist across the long axis of gut.
• Most common in the colon of the pig and the horse

Intussusception

Diagram of intussuscception (Courtesy of Elspeth Milne)

• Telescoping of one segment of the bowel into another.
• Occurs in all species.
  • Particularly in young dogs.
• Can occur in the small intestine, caecum or colon.

Clinical

• Intussusception is a less acute type of obstruction.
• Produces intermittent diarrhoea.
• Animals go downhill in a few days.
• Palpation of abdomen may allow a "Cumberland sausage" effect to be felt.
  • NB abdominal palpation in small animal, rectal palpation in large animal.

Pathogenesis

• Proximal intestine invaginates into lower part of intestine.
  

  Intersusception (Courtesy of Bristol BioMed Image Archive)
  • Takes mesenteric attachment with it.
• Compression of the mesenteric vessels obstructs venous drainage of the gut, resulting in venous congestion.
  • Swelling (oedema/congestion) arises.
    • Inflammatory exudate from serous surface.
      • Fibrinous adhesions form between surfaces making structure irreducible.
• May progress to necrosis and gangrene of the tissue.
• There is often functional obstruction to bowel.
• May rupture, leading to peritonitis and death.
• Associated with anything that raises peristalsis e.g. change in diet, bacterial infection.
  • Foreign body
  • Intramural abscess/tumour
  • Heavy parasitism
  • Previous intestinal surgery
  • Enteritis
  • Other motility disorders.
  • Change in diet
  • Bacterial infection

Pathology

• When operate or at post mortem see large sausage shaped distension of length of intestine.

• Intussusception may occur post mortem
  • There are no associated changes
  • The condition is easilt reducible.

Rectal prolapse

• Pig, sheep, cattle
• Related to prolonged tenesmus, e.g.
  • Colitis
  • Urinary infection
  • Obstruction
  • Hepatic failure.

References

Brown CC, Baker DC, Barker IK: Alimentary System. In: Jubb, Kennedy and Palmer's Pathology of Domestic Animals, ed. Maxie MG, 5th ed., pp. 1-296. Elsevier, Philadelphia, PA, 2007.

McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393.Elsevier, St. Louis, Missouri, 2007.