• Clinical science



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 enterocolitis) 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).



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
  • 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
  • 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
      • 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
      • Colonoscopic bowel decompression: indicated if neostigmine is contraindicated or unsuccessful
    • Surgery
      • Indications
        • Signs of impending or actual colonic ischemia/perforation or peritonitis
        • Failure of conservative therapy
      • Cecostomy
      • Colectomy with/without colostomy


Chronic megacolon (chronic colonic pseudo-obstruction)

References:[1][11][12][3][13][14][15][16][2][10][17][18][19][20] [21]

Toxic megacolon

Colonoscopy should be avoided in patients with suspected toxic megacolon since it increases the risk of colonic perforation.

  • 1. Bharucha AE, Phillips SF. Megacolon: Acute, toxic, and chronic. Curr Treat Options Gastro. 1999; 2(6): pp. 517–523. doi: 10.1007/s11938-999-0055-9.
  • 2. Cagir B. Intestinal Pseudo-Obstruction. In: Geibel J. Intestinal Pseudo-Obstruction. New York, NY: WebMD. http://emedicine.medscape.com/article/2162306. Updated January 5, 2016. Accessed January 29, 2017.
  • 3. O'dwyer RH, Acosta A, Camilleri M, Burton D, Busciglio I, Bharucha AE. Clinical Features and Colonic Motor Disturbances in Chronic Megacolon in Adults. Dig Dis Sci. 2015; 60(8): pp. 2398–2407. doi: 10.1007/s10620-015-3645-5.
  • 4. Camilleri M. Acute colonic pseudo-obstruction (Ogilvie's syndrome). In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/acute-colonic-pseudo-obstruction-ogilvies-syndrome. Last updated March 26, 2015. Accessed January 29, 2017.
  • 5. Gamarra RM. Acute Megacolon. In: BS Anand. Acute Megacolon. New York, NY: WebMD. http://emedicine.medscape.com/article/180872. Updated October 31, 2016. Accessed January 29, 2017.
  • 6. Vanek VW, Al-salti M. Acute pseudo-obstruction of the colon (Ogilvie's syndrome): An analysis of 400 cases. Dis Colon Rectum. 1986; 29(3): pp. 203–210. pmid: 3753674.
  • 7. Maloney N, Vargas HD. Acute intestinal pseudo-obstruction (Ogilvie's syndrome). Clin Colon Rectal Surg. 2005; 18(2): pp. 96–101. doi: 10.1055/s-2005-870890.
  • 8. Jain A, Vargas HD. Advances and challenges in the management of acute colonic pseudo-obstruction (ogilvie syndrome). Clin Colon Rectal Surg. 2012; 25(1): pp. 37–45. doi: 10.1055/s-0032-1301758.
  • 9. Geller A, Petersen BT, Gostout CJ. Endoscopic decompression for acute colonic pseudo-obstruction. Gastrointest Endosc. 1996; 44(2): pp. 144–150. pmid: 8858319.
  • 10. Beattie GC, Peters RT, Guy S, Mendelson RM. Computed tomography in the assessment of suspected large bowel obstruction. ANZ J Surg. 2007; 77(3): pp. 160–165. doi: 10.1111/j.1445-2197.2006.03998.x.
  • 11. Camilleri M. Chronic intestinal pseudo-obstruction. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/chronic-intestinal-pseudo-obstruction. Last updated July 18, 2016. Accessed January 29, 2017.
  • 12. Manuel D. Chronic Megacolon. In: BS Anand. Chronic Megacolon. New York, NY: WebMD. http://emedicine.medscape.com/article/180955. Updated March 28, 2016. Accessed January 29, 2017.
  • 13. Hanauer SB, Wald A. Acute and chronic megacolon. Curr Treat Options Gastroenterol. 2007; 10(3): pp. 237–247. pmid: 17547862.
  • 14. Camilleri M. Disorders of gastrointestinal motility in neurologic diseases. Mayo Clin Proc. 1990; 65(6): pp. 825–846. pmid: 2164123.
  • 15. Matsuda NM, Miller SM, Evora PR. The chronic gastrointestinal manifestations of Chagas disease. Clinics. 2009; 64(12): pp. 1219–1224. doi: 10.1590/S1807-59322009001200013.
  • 16. Gladman MA, Knowles CH. Novel concepts in the diagnosis, pathophysiology and management of idiopathic megabowel. Colorectal Dis. 2008; 10(6): pp. 531–538. doi: 10.1111/j.1463-1318.2007.01457.x.
  • 17. Kim ER, Rhee PL. How to interpret a functional or motility test - colon transit study. J Neurogastroenterol Motil. 2012; 18(1): pp. 94–99. doi: 10.5056/jnm.2012.18.1.94.
  • 18. Maurer AH. Gastrointestinal Motility, Part 2: Small-Bowel and Colon Transit. http://jnm.snmjournals.org/content/56/9/1395.full. Updated July 9, 2015. Accessed January 29, 2017.
  • 19. Ranjan P, Bansal N, Sachdeva M, Jain P, Arora A. Colonic Transit Time: Current Methodology and its Clinical Implications. JIMSA. 2012; 25(1): p. 35. url: http://medind.nic.in/jav/t12/i1/javt12i1p35.pdf.
  • 20. Wesson DE. Congenital aganglionic megacolon (Hirschsprung disease). In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/congenital-aganglionic-megacolon-hirschsprung-disease. Last updated November 9, 2016. Accessed December 22, 2016.
  • 21. Farmer AD, Scott SM, Hobson AR. Gastrointestinal motility revisited: The wireless motility capsule. United European Gastroenterology Journal. 2013; 1(6): pp. 413–421. doi: 10.1177/2050640613510161.
  • 22. Weiner BC. Ulcerative colitis in adults. http://www.dynamed.com/topics/dmp~AN~T114507#Colonic-complications. Updated May 13, 2019. Accessed July 16, 2019.
  • 23. Lin B. Toxic megacolon Treatment & Management. https://emedicine.medscape.com/article/181054-treatment. Updated March 1, 2018. Accessed July 16, 2019.
  • 24. Lin B. Toxic Megacolon. In: Cagir B. Toxic Megacolon. New York, NY: WebMD. http://emedicine.medscape.com/article/181054. Updated November 20, 2016. Accessed January 10, 2017.
  • 25. Sheth SG, Lamont JT. Toxic megacolon. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/toxic-megacolon. Last updated October 15, 2015. Accessed January 30, 2017.
  • 26. Sheth SG, Lamont JT. Toxic megacolon. Lancet. 1998; 351(9101): pp. 509–513. doi: 10.1016/S0140-6736(97)10475-5.
  • 27. Ausch C, Madoff RD, Gnant M, et al. Aetiology and surgical management of toxic megacolon. Colorectal Dis. 2005; 8(3): pp. 195–201. doi: 10.1111/j.1463-1318.2005.00887.x.
  • 28. Gan SI, Beck PL. A new look at toxic megacolon: an update and review of incidence, etiology, pathogenesis, and management. Am J Gastroenterol. 2003; 98(11): pp. 2363–2371. doi: 10.1111/j.1572-0241.2003.07696.x.
  • 29. Mourelle M, Casellas F, Guarner F et al. Induction of nitric oxide synthase in colonic smooth muscle from patients with toxic megacolon. Gastroenterology. 1995; 109(5): pp. 1497–1502. doi: 10.1016/0016-5085(95)90636-3.
last updated 11/03/2020
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