From Dog
Typical radiographic appearance of a dog with constipation due to megacolon[1]

Megacolon is a relatively uncommon intestinal disorder of dogs characterized by intractable constipation, abdominal distension and hypertrophy of the colon.

This condition is less commonly reported compared to megacolon in cats and may be a congenital disease or acquired later in life.

In dogs, diet is the most important local factor affecting colonic function and the quality of feces formed in the colon. As well, ileal distension appears to play a role in the initiating cascade of reflex colonic relaxation and distension in the dog[2].

Large-breed dogs appear predisposed, and other factors may aggravate the condition such as:

  • dietary bone meal, dietary calcium supplementations
  • inactivity
  • chronic constipation
  • autonomic ganglioneuritis[3]
  • pelvic injury

When dried and concreted feces remains lodged in the colon for prolonged periods, distention of the colon results in irreversible colonic inertia.

Clinically affected dogs have a protracted history of constipation non-responsive to medical intervention with prokinetic drugs[4]. The affected dogs strains to defecate with passage of only small or no fecal volume.

Diagnosis is usually confirmed by a history of intermittent dyschezia, abdominal palpation, plain radiography and postoperative histopathological findings. During exploratory laparotomy, megacecum has also been reported[5].

Treatment normally requires subtotal colectomy with preservation of the ileocolic junction[6].


  1. Vetnext
  2. Basilisco G & Phillips SF (1994) Ileal distention relaxes the canine colon: a model of megacolon? Gastroenterology 106(3):606-614
  3. Petrus DJ et al (2001) Megacolon secondary to autonomic ganglioneuritis in a dog. Vet Rec 148(9):276-277
  4. Washabau RJ et al (2003) Gastrointestinal motility disorders and gastrointestinal prokinetic therapy. Vet Clin North Am Small Anim Pract 33(5):1007-1028
  5. Bright RM et al (1986) Subtotal colectomy for treatment of acquired megacolon in the dog and cat. J Am Vet Med Assoc 188(12):1412-1416
  6. Nemeth T et al (2008) Long-term results of subtotal colectomy for acquired hypertrophic megacolon in eight dogs. J Small Anim Pract 49(12):618-624