Colonic Impaction - Dog and Cat

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Also known as: Faecal impaction — Constipation — Obstipation


Colonic impaction is intractable constipation which can occur in all species, including the dog and cat. There are hardened faeces in the colon and a delayed or failure of faecal passage. The slower transit time allows more salt and water to be reabsorbed, leaving drier faeces in the colon which are more difficult to pass. Peristalsis may increase initially but is then significantly reduced or even absent due to chronic distension. Chronic cases may progress to obstipation, the faeces become so hard and dry that defecation is no longer possible and ultimately there is secondary degeneration of the colonic musculature.

There are numerous causes which can be categorised as follows:

An abnormal diet with insufficient water content, scavenging or ingestion of indigestible material such as plastics, certain plants, hair and bones can all cause problems.

Mechanical obstruction
An obstruction of the colon or rectum will cause faecal material to become impacted and dry. The obstruction may be intraluminal such as a foreign body, polyp, mass or stricture. Extraluminal obstruction can be due to a mass, abscess, and prostatic diseases such as prostatic cyst, mass and prostamegaly. A diverticulum to the colon or rectum, or a perineal hernia interupts the normal passage of faeces and may result in an impaction.

Colonic weakness
A systemic disease causing abnormalities in electrolytes, such as hypercalcaemia, hypokalemia can affect peristaltic contractions; the endocrine disorder hypothyroidism also results in colonic weakness. Idiopathic megacolon is a significant cause of impaction especially in cats.

Problems with defecation
Environmental and behavioural factors are also important; a change in routine or household, or excessive stress can prevent animals from defecating normally. Animals also avoid defecation if it is painful due to anal sac disease, trauma to the perineal area, or they are unable to assume a normal position to defecate because of a fractured pelvis or another orthopaedic, condition.


Animals most commonly affected depend on the cause of the impaction. Significant risk factors include metabolic disease causing dehydration,inappropriate diet, and drug therapy affecting gastrointestinal motility such as opioids and anticholinergics.


Clinical signs

  • Failure to pass faeces
  • Tenesmus
  • Dyschezia
  • Anorexia
  • Lethargy
  • Vomiting

On abdominal palpation the colon is filled with firm faecal material. Digital rectal examination will reveal hardened faecal balls; there may be a palpable mass or stricture, anal sac disease or perineal hernia depending on the cause.


Abdominal ultrasound shows a colon impacted with faecal material. It may also reveal the cause in some cases such as foreign body, colonic mass, enlarged prostate or stricture.


Abdominal radiographs reveal a colon filled with faecal material. Radiographs are not normally needed to make a diagnosis of colonic impaction as it can usually be identified on clinical exam; however in certain cases it can identify the cause. A fractured pelvis, dislocated hip, enlarged prostate and colonic or rectal masses can be found on radiographs.


Colonoscopy will identify a colonic or rectal mass or stricture and facilitates obtaining biopsy specimens.


The treatment depends on the severity and duration of the impaction.

Dehydrated patients should receive IV fluid therapy, with correction of any concurrent electrolyte and acid-base abnormalities. A warm water enema can be used to soften and allow the impaction to pass. Laxatives such as emollient laxatives (docusate sodium), stimulant laxatives (bisacodyl), saline laxatives and disaccharide laxatives (lactulose) are also beneficial. Mineral oil and white petroleum lubricants should be avoided due to the risk of aspiration because of their tasteless nature.

Cisapride, a motility modifier is indicated in early cases of megacolon but is contraindicated in cases of obstruction.

Owners should be educated with regard to management. An appropriate wet diet should be fed, dietary supplementation with bran is helpful in some cases, fresh water should be freely available and activity should be encouraged.

Antidiurectic and anticholinergic drugs should be avoided.


Surgical removal of faeces under general anaesthesia is necessary in severe cases where enemas and laxatives have been unsuccessful. A colectomy is required in cases of obstipation or recurrent cases.


Prognosis varies depending on the underlying cause.

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Colonic Impaction in cats and dogs


  • Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition) Elsevier Science
  • Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
  • Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.
  • Tilley, L.P. and Smith, F.W.K.(2004)The 5-minute Veterinary Consult(Third edition) Lippincott, Williams & Wilkins.

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