Category:Obstruction, Intestinal

Intestinal obstruction can be the sequel to either mechanical or functional causes. Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction (Brown et. al, 2007).

Mechanical Obstruction

• Acute of chronic mechanical obstruction of the intestine can occur in all species.
  • Acute obstruction usually involves the upper or middle small intestine
  • Chronic obstruction typically occurs in the distal small intestine or large intestine.
• Three main categories of causes of obstruciton:
  • Intraluminal
    • E.g. foreign bodies, food impaction.
  • Intramural
    • E.g. neoplasia
  • Extrinsic
    • E.g. adhesions, neoplasia and prostate enlargement.

Intraluminal Obstruction

Foreign Bodies

• Foreign bodies of all types can be found in the intestines.
• While some may pass through posing no problems, others can cause acute obstruction,
• Quite common in dogs
  • Rare in other species - tend to lodge in the oesophagus or in one of the ruminant stomachs.)
  • Enteroliths can be seen in horses greater than 4 years of age.
    • Are stones consisting of magnesium ammonium phosphate around a central nidus (often a metallic foreign body)
    • Typically lodge at the pelvic flexure or the transverse colon.
• Clinical
  • Obstruction at pylorus produces repeated vomiting.
  • Obstrustion lower down gives less dramatic effect.
    • Is still a problem if in the middle of the small intestines.
    • May be vague signs; some vomiting and off food.
• Diagnosis
  • May not show up well radiographically (unless radio-opaque) for several days.
    • May also be objects that are semi solid or soft, e.g.
      • String
      • Plastic bags
      • Stringy things, like pieces of material- particularly in puppies.
  • Make all of intestines have knotted appearance.
  • May be seen in horses with baler twine.
• Pathogenesis
  • Smooth, round objects, such as golf balls, lodge especially near the pylorus or lower down.
  • Occasionally in cattle (piece of rope or piece of tarpaulin) produces a tangled mass in rumen.
  • Cause pressure necrosis and eventually perforation.
  • Foreign bodies can also be chronic, remaining for long periods of time without causing disturbance.

Impaction

• Impaction of the colon can occur in all species.
  • Dog and cat - main cause is dehydrated faecal material.
  • Horse - faeces, digesta, sand, or fibrous material can all contribute.
    • There are certain predisposing factors:
      • Poor dentition
      • Water deprivation
      • A high roughage diet
      • General debility.
• Antihelminthic administration or large parasite burdens can also lead to impaction.

Extrinsic Obstruction

• Obstruction of the intestine due to external factors such as tumours, abscesses, and fibrous adhesions is a common occurrence.

Inflammatory Adhesions

colonic adhesions in the horse (Courtesy of Elspeth Milne)

• Arise following gut perforation, peritonitis or surgery.
• Consist of fibrous tissue bands that may:
  • Restrict intestinal motility
  • Cause kinks in the mesentery.

Prostatic Enlargement

• In the dog
• Can lead to compression of the rectum

Neoplasia

• Neoplasi in structures adjacent to the intestines can spread and cause external compression.
• Pancreatic tumours in particular can extend and impinge on the duodenum.
• Pedicles of tumours such as lipomas in horses can become wound in loops of intestine leading to obstruction and possible strangulation.

Closeup of a pedunculated lipoma (Courtesy of Elspeth Milne)

• Clinical
  • Occasional vomiting and ntermittent diarrhoea over several weeks.
• Pathogenesis
  • Seen occasionally in cat (rarer in dog)
  • Usually towards end of intestines
    • E.g. at the ileocaecocolic valve.
  • Gut proximal to tumour becomes thickened due to hypertrophy of smooth muscle as a result of trying to force ingesta past progessively narrowing lumen.
  • Produces "hose pipe intestine".
  • Seen with carcinoma, lymphoma, leiomyoma and other tumours.

Functional Obstruction

Paralytic Ileus

• A common condition.
• Occurs following trauma or abdominal surgery.
• Stasis of gut flow due to failure of peristalsis.
  • Leads to distension with gas and fluid, as well as a flaccid intestinal wall.

Causes

• Anything which stops peristalsis, e.g.
  • Damage to nerve supply to intestine (autonomic nervous system)
  • Pain
  • Abnormal metabolism
  • Toxaemia
  • Electrolyte imbalance such as hypocalcaemia, hypomagnesaemia, and hypokalaemia.
• Also in
  • Diabetes mellitus
  • Uraemia
  • Tetanus
  • Lead poisoning.

Pathology

• loss of smooth muscle tone leads to a flaccid bowel.
• Bowel is distended with fluid.

Pathogenesis

• Intestine susceptible to neurogenic damage during an operation.
• Peristalsis fades away over a few days producing paralytic (adynamic) ileus.
• Particularly occurs if bowel handled roughly, or if serosa gets cold and dry at surgery.
• Very difficult to start peristalsis again but will sometimes respond to pharmacological or electrical stimulation.
• The horse is very susceptible, and the dog is somewhat suscpeitble.

Dysautonomia

• Most notably affects horses and cats.

Equine dysautonomia, or grass sickness

• Most prevalent in the UK and western Europe.
  • Common in wetter areas, e.g. the South West.
• Seen in horses out at pasture in late summer and autumn.
• Usually affects young adults.
  • 6-7 years old.
• Clinical
  • Acute oneset:
    • Muscular tremors
    • Abdominal pain
    • Does not eat
    • Constipation
    • Become severly tympanic in acute cases
    • Dull and restless
    • Avoid swallowing
    • Salivate excessively
  • Degenerative lesions are seen in the autonomic nerve ganglia, including enteric plexuses
  • May either:
    • Progress rapidly to death
    • Take a slower clinical course.
      • Eat a bit, but food drops out of mouth
      • Go on to die slowly.
  • Some horses recover
    • This is very unlikely, and the condition is usually fatal.
  • Clinically difficult to diagnose - signs are confined to the gut.
    • Easy to diagnose on post mortem
• Pathology
  • Stomach and small intestine large amounts of contain watery yellow fluid.
    • There is an abrupt change in the large intestine, where no fluid is present.
      • large intestine has very dry mucoid contents.
• Pathogenesis
  • Due to functional obstruction at ileocaecal valve and a degree of paralytic ileus of the small intestine.
  • The exact cause is unknown, but a type of bacterial or fungal toxin which may damage autonomic nervous system ganglia may be involved.
    • Clostridium botulinum is thought to be involved.
• A similar condition seen in hares
  • Certain yeares almost seem to have outbreaks.
• Certain pastures at certain times of year produce grass sickness quite often.
  • A definitive diagnosis must be made - if the condition is due to the grazing we need to know.
    • E.g. if on livery or stud grazing, may put people off going there.
• 'Diagnosis
  • At post mortem look for degenerative changes in coeliaco-mesenteric ganglia - need to examine histologically.
    • Ganglia are peanut sized and found in perirenal fat between adrenal gland and the aorta.

Feline dysautonomia, or Key-Gaskell Syndrome

Histological section of degenerate neuron in feline dysautonomia(Courtesy of Susan Rhind)

• Occurs mostly in the UK and continental Europe.
• Is also of unknown aetiology. Suggested causative factors include:
  • Environmental toxins
  • Infectious agents
  • Botulinum toxins .
• Clinical signs:
  • Anorexia
  • Depression
  • Bradycardia
  • Decreased lacrimation,
  • Altered pupillary dilataion,
  • Megaoesophagus
  • Constipation.
• Degenerative lesions of autonomic nerve ganglia can be seen.
• Also occurs in the oesophagus.