Difference between revisions of "Category:Obstruction, Intestinal"

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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.
  • 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.
  • 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
  • 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
  • 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.
  • 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.

Subcategories

This category has the following 2 subcategories, out of 2 total.