Canis ISSN: 2398-2942

Megacolon

Contributor(s): Lori Ludwig, James Simpson

Introduction

  • Condition of the bowel in which the colon becomes chronically enlarged and hypermotile.
  • Causes: chronic constipation due to dietary indiscretion or narrowing of the pelvis following trauma; motility disorders due to intrinsic or extrinsic neurogenic causes; unknown factors.
  • Signs: tenesmus and/or observed lack of defecation.
  • Diagnosis: history, physical examination, clinical signs and radiography.
  • Treatment: re-establish normal fluid and electrolyte abnormalities, attempt to empty the feces-filled colon, a subtotal colectomy (95-98% of the colon) with or without the removal of the ileocolic valve.
  • Medical management: deobstipation followed by high fiber diet, laxatives (lactulose) and prokinetic agents (cisapride).
  • Prognosis: expect 50% recurrence rate. Prognosis with surgery can be good to excellent in cats with minimal recurrence in most cases. However, chronic diarrhea may occur.

Pathogenesis

Etiology

  • Chronic constipation due to dietary indiscretion.
  • Narrowing of the pelvis:
  • Motility disorder due to intrinsic or extrinsic neurogenic causes:
    • Sacral spinal cord degeneration.
    • Disautonomia Dysautonomia.
  • Colonic stricture:
  • Unknown factors.

Predisposing factors

General
  • History of trauma and a progressive problem with constipation.
  • Pelvic deformity.
  • Stricture due to chronic inflammation.
  • Denervation secondary to a lower spine injury.
  • Primary tumors involving the colon Intestine: linear foreign bodies or extracolonic structures.

Pathophysiology

  • Water resorption from retained feces leads to fecal concretions which are difficult to pass. Prolonged retention of feces and distention of the colon results in damage to smooth muscle and nerved and ultimately colonic inertia.
  • Progressive disease since dilation → stretching of smooth muscle → reduced contractility.
  • Water resorption from stagnant feces → dry fecal boluses which are difficult to pass.
  • Side-effects of constipation include lethargy, anorexia, dehydration and occasionally vomiting.
  • Absorption of bacteria/toxins from retained feces can lead to lethargy, anorexia and vomiting. Vomiting may also result from vagal stimulation (secondary to bowel distention).

Timecourse

  • Days to weeks.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schrader S C (1992) Pelvic osteotomy as a treatment for obstipation in cats with acquired stenosis of the pelvic canal - 6 cases (1978-1989). JAVMA 200 (2), 208-13 PubMed.
  • Matthiesen D T, Scavelli T D, Whitney W D (1991) Subtotal colectomy for the treatment of obstipation secondary to pelvic fracture malunion in cats. Vet Surg 20 (2), 113-7 PubMed.
  • Rosin E et al (1988) Subtotal colectomy for treatment of chronic constipation associated with idiopathic megacolon in cats - 38 cases (1979-1985). JAVMA 193 (7), 850-3 PubMed.
  • Bright R M, Burrows C F & Goring R et al (1986) Subtotal colectomy for treatment of acquired megacolon in the dog and cat. JAVMA 188 (12), 1412-1416 PubMed.


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