• Clinical science

Megacolon

Abstract

Megacolon is the dilation of the colon in the absence of a mechanical obstruction (e.g., colonic tumor/stricture). There are three etiological types of megacolon: acute, chronic, and toxic megacolon. Acute megacolon (Ogilvie's syndrome) is the acute dilation of the colon, characteristically seen in severely medically/surgically ill patients, probably secondary to an electrolyte/metabolic imbalance. Chronic megacolon is the permanent dilation of the colon caused by chronic colonic dysmotility due to an underlying neuropathic (Hirschsprung's disease, chronic Chagas disease) or myopathic (Duchenne's muscular dystrophy) disorder. Patients with acute/chronic megacolon typically present with abdominal pain, bloating, and constipation. Toxic megacolon is a life-threatening dilation of the colon associated with systemic toxicity due to infectious colitis (C. difficile pseudomembranous colitis, Salmonella colitis) or inflammatory colitis (inflammatory bowel disease). Patients typically present with signs of sepsis (tachycardia, hypotension) and a history of abdominal pain and bloody diarrhea. Abdominal x-rays demonstrate a colonic dilation, with/without air-fluid levels, and without haustrae. Contrast-enhanced CT scans can identify/rule out a mechanical colonic obstruction and possible complications (colonic ischemia/perforation). Patients with acute/chronic megacolon can often be treated conservatively with bowel rest, dietary modifications, prokinetic drugs, and/or neostigmine. Colonoscopic decompression is often successful in patients with acute megacolon. Surgical intervention for acute/chronic megacolon (colectomy and ileorectal anastomosis) is indicated if conservative treatment fails. Conservative management of toxic megacolon includes bowel rest, IV antibiotics (for infectious colitis), IV steroids (for inflammatory bowel disease). There is a high risk of colonic perforation in patients with toxic megacolon. Hence, no improvement to medical therapy within 48–72 hours is an indication to perform surgery (subtotal colectomy and end ileostomy).

Classification

References:[1][2][3]

Acute megacolon (Acute colonic pseudo-obstruction or Ogilvie's syndrome)

  • Description: Acute dilation of the colon in the absence of a mechanical obstruction; , characteristically seen in severely ill or postoperative patients
  • Etiology
  • Pathophysiology
    • Etiological factorsimpairment/destruction of the autonomic nervous systemimbalance between sympathetic and parasympathetic control of intestinal motility → accumulation of feces, air, and intestinal secretions in the intestine → colonic dilation
  • Clinical features
  • Diagnostics
    • Laboratory values: may show signs of underlying disease; hypokalemia as a potential cause
    • Abdominal x-ray: dilation of the cecum and right colon (occasionally up to the rectum) with/without multiple air-fluid levels; haustrae are preserved
    • Contrast enhanced CT scan(oral and IV contrast)
      • Confirms x-ray findings
      • Rules out mechanical obstruction (e.g., tumor/stricture)
      • Can diagnose complications (ischemic bowel segments or perforation peritonitis)
    • Colonoscopy and endoscopy: indicated in hemodynamically stable patients when CECT cannot be performed; rules out a mechanical obstruction Colonoscopic decompression of acute megacolon can be performed in the same sitting.
  • Treatment
    • Conservative management
      • Supportive measures
        • Indications: patients with mild symptoms and cecal dilation < 12 cm
        • Treat the inciting factor
        • IV fluids and bowel rest (NPO)
        • Bowel decompression
          • Nasogastric tube to decompress the stomach
          • Rectal tube to decompress the rectum and distal colon
      • Pharmacologic management: Neostigmine
        • Indications
          • No improvement > 24–48 hours of bowel rest and decompression
          • Cecal dilation > 12 cm and no signs of colonic ischemia/perforation or peritonitis
        • Methylnaltrexone: may be attempted if opiates are suspected as a precipitating factor
      • Colonoscopic bowel decompression: indicated if neostigmine is contraindicated or unsuccessful
    • Surgery
      • Indications
      • Cecostomy
      • Colectomy with/without colostomy

References:[4][5][6][7][8][9][2][10]

Chronic megacolon (chronic colonic pseudo-obstruction)

  • Description: Permanent dilation of the colon caused by congenital/acquired colonic dysmotility in the absence of a mechanical obstruction
  • Etiology
  • Pathophysiology: Etiological factors cause a neural and/or motor dysfunction of the bowel → bowel dysmotility → progressive colonic dilation
  • Clinical features
    • Recurrent episodes of:
    • Examination findings: Abdominal distention; mild abdominal tenderness
    • Signs and symptoms of the underlying disorder
  • Diagnostics
    • Laboratory values: may show signs of underlying disease
    • Abdominal x-ray: dilation of the cecum and right colon (occasionally up to the rectum) with/without multiple air-fluid levels; haustrae are preserved
    • Contrast-enhanced CT scan (CECT; oral and IV contrast)
      • Confirms x-ray findings
      • Rules out mechanical obstruction (e.g., tumor/stricture)
      • Can diagnose complications (ischemic bowel segments or perforation peritonitis)
    • Colonoscopy and endoscopy: indicated in hemodynamically stable patients when CECT cannot be performed; rules out a mechanical obstruction Colonoscopic decompression of acute megacolon can be performed in the same sitting.
    • Assessment of colonic motility
      • Colon transit scintigraphy: Investigation of choice to diagnose and determine the extent of delayed colonic transit
      • Colon transit test using radio-opaque markers
      • Wireless motility capsule
    • Manometry
    • Colonic biopsy
  • Treatment
    • Conservative management
    • Surgery: : indicated in patients who do not improve/worsen on conservative therapy

References:[1][11][12][3][13][14][15][16][2][10][17][18][19][20]

Toxic megacolon

Coloscopy should be avoided in patients with suspected toxic megacolon since it increases the risk of colonic perforation.
References:[21][13][22][23][24][25][26][10]

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last updated 09/06/2018
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