Megacolon

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• Extreme dilation of the colon leading to severe constipation.
• Cause: primary - idiopathic, may be disorder of smooth muscle function; secondary to any lesion preventing normal defecation over a long period, eg neoplasia, strictures, foreign bodies, extramural compression of colon.
• Signs: lethargy, anorexia, constipation, ptyalism, vomiting, tenesmus.
• Diagnosis: abdominal palpation, radiography.
• Treatment: initially - fluid therapy, remove cause, laxatives and enemas; long-term - diet and bulk-forming agents, prokinetics, eg cisapride; surgery - subtotal colectomy for irreversible cases.
• Prognosis: guarded depending on stage of disease and choice of treatment.

• Older cats - primary megacolon.

• Idiopathic - dysfunction of colonic smooth muscle, progressive post-receptor defect in excitation-contraction coupling.
• Secondary to colonic obstruction - extraluminal compression, eg pelvic fracture, intraluminal masses or strictures, functional disorders, eg neuromuscular disease, congenital anomalies, metabolic disorders.

• Colonic neoplasia, eg lymphosarcoma .

• Foreign bodies.
• Extramural colonic compression.
• Strictures.

• Smooth muscle dysfunction OR other primary disease normal defecation prevented over prolonged period colon distends muscle degenerates colon flaccid and filled with dry, hard fecal material.

• Constipation .
• Tenesmus.
• Anorexia.
• Vomiting .

• Constipation.

• Tenesmus.
• Vomiting.
• Ptyalism (sign of nausea).
• Anorexia.
• Weight loss.

• Palpable colon, distended with hard material.

• Depressed.
• Unkempt appearance.

• Palpation of secondary cause, eg pelvic fracture, abdominal mass.
   Perform neurological and anorectal examination to rule out possible secondary causes.

• Dehydration.

• Colon distended with impacted fecal material .
• Possible secondary causes, eg fracture, radio-opaque foreign body, other lesions, eg spinal, abdominal.
• Contrast radiography following evacuation of colon to detect intraluminal obstruction.

• To guide supportive therapy.

• Neuromuscular function tests.

• Palpation of fecal-filled colon.

• Radiography.

• Examination requires removal of ventral coxal bones by cutting cranially and caudally from each obturator foramen. Complete exposure essential to rule out obstruction/compression.
   Beware, adenocarcinoma resembles fibrous structure grossly, so histopathology essential.
   Consider examining spinal cord and nerve supply for neurological causes.

• Fix colon and colonic nodes for histology. Include autonomic ganglia, spinal cord and nerves if possible. Include multiple samples from remainder of gastrointestinal tract.

• Megacolon occasionally associated with lymphocytic inflammation of myenteric ganglia. Cause unknown.

• Causes of constipation .

• Colitis .

• Restore electrolyte and fluid balance .
• Remove fecal concretions under general anesthesia .
  • Instil 30-40 ml warm isotonic electrolyte solution into rectum.
     Rapid instillation of enema can induce vomiting even in anesthetized patients, so use cuffed endotracheal tube.
  • Massage gently through the abdominal wall.
  • Removal of feces with whelping or sponge forceps.
  • Administer corticosteroid and antibiotic ointment combined 3:1 with lidocaine ointment into rectum to treat proctitis .
• Remove inciting cause if possible.
• Diet - feed low-residue, highly digestible diet .
• Lactulose (bulk forming agent), usual dose is 1 ml/kg SID, but can titrate for individual.
   Mix with milk to improve palatability.
• Cisapride (stimulates colonic motility) 0.3-0.4 mg/kg TID.

Surgery

• If failure to respond to medical management, ie changes in colonic smooth muscle are irreversible, or poor compliance with medical treatment:
  • Subtotal colectomy.
  • Resect colon from just above or below the ileocolonic junction to a point immediately proximal to the pubic brim.
  • Anastomose ileum or proximal colon to terminal colon in end-to-end or side-to-side fashion.
  • Results usually in soft to semi-solid fecal consistency.
     Preservation of ileo-colic valve reduces incidence of diarrhea post-operatively.

• Repeat enemas may be necessary in cases managed medically.

• Guarded: depends on stage of disease at diagnosis and owner compliance, (long-term dietary and medical management required).
• Good: if treated with subtotal colectomy.

• Control of constipation.

• Progression of disease.
• Standard reasons .

• Bertoy RW (2002) Megacolon in the cat. Vet Clin North Am Small Anim Pract. 32 (4), 901-915

• Prof Ed Hall MA VetMB PhD DipECVIM MRCVS
• Dr Philip K Nicholls BVSc BSc PhD MRCVS FRCPath

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