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Megacolon

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Megacolon
Toxic megacolon associated withulcerative colitis.
SpecialtyGastroenterologyEdit this on Wikidata

Megacolonis an abnormal dilation of thecolon(also called the largeintestine).[1][2]This leads tohypertrophyof the colon.[2]The dilation is often accompanied by aparalysisof theperistalticmovements of the bowel. In more extreme cases, thefecesconsolidate into hard masses inside the colon, calledfecalomas(literally,fecal tumor), which can requiresurgeryto be removed.

A human colon is considered abnormally enlarged if it has adiametergreater than 12cm[3]in thececum(it is usually less than 9 cm[4]), greater than 6.5 cm[3]in therectosigmoidregion and greater than 8 cm[3]for theascending colon.The transverse colon is usually less than 6 cm in diameter.[4]

A megacolon can be eitheracuteorchronic.It can also be classified according to cause.[5]

Signs and symptoms[edit]

External signs and symptoms areconstipationof very long duration,[2]abdominalbloating,abdominal tenderness andtympany,abdominal pain,palpationof hard fecal masses and, in toxic megacolon,fever,low bloodpotassium,tachycardiaand may lead toshock.Stercoral ulcersare sometimes observed in chronic megacolon, which may lead to perforation of the intestinal wall in approximately 3% of the cases, leading tosepsisand risk of death.[6][7]

Cause[edit]

Aganglionic megacolon[edit]

Also calledHirschsprung's disease,it is acongenitaldisorder of the colon in whichnerve cellsof themyenteric plexusin its walls, also known as ganglion cells, are absent. It is a rare disorder (1:5 000), with prevalence among males being four times that of females. Hirschsprung's disease develops in thefetusduring the early stages ofpregnancy.A genetic predisposition to Hirschsprung's disease has been linked tochromosome 13where amissense mutationat an ultraconserved region impairs functionality of the W276C receptor. Seven other genes seem to be implicated, however. If untreated, the patient can developenterocolitis.[citation needed]

Medication[edit]

Risperidone,an anti-psychotic medication, can result in megacolon.[9]

Toxic megacolon[edit]

Main article:Toxic megacolon

Toxic megacolon is mainly seen inulcerative colitisandpseudomembranous colitis,two chronicinflammationsof the colon (and occasionally, in the other type ofinflammatory bowel disease,Crohn's disease). Its mechanism is incompletely understood. It is probably due to excessive production ofnitric oxide,at least in ulcerative colitis. The prevalence is about the same for both sexes.[citation needed]

In patients with HIV/AIDS,cytomegalovirus(CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy. CMV may also increase the risk of toxic megacolon in non-HIV/AIDS patients with IBD.[10]

Chagas disease[edit]

Megacolon can be associated withChagas disease.[11]Chagas disease is caused byTrypanosoma cruzi,a flagellateprotozoantransmitted by theassassin bug.Chagas disease can also be acquired congenitally, through blood transfusion or organ transplant, and rarely through contaminated food (for examplegarapa). There are several theories on how megacolon (and alsomegaesophagus) develops in Chagas disease. TheAustrian-BrazilianphysicianandpathologistFritz Köberlewas the first to propose theneurogenic hypothesisbased on the documented destruction of themyenteric plexusin the walls of the intestinal tracts of Chagas patients. In this, the destruction of theautonomic nervous systeminnervation of the colon leads to a loss of the normalsmooth muscletone of the wall and subsequent gradual dilation. His research proved that, by extensively quantifying the number of neurons of the autonomic nervous system in the Auerbach's plexus, that:[citation needed]

  1. neurons were strongly reduced all over the digestive tract;
  2. megacolon appeared only when there was a reduction of over 80% of the number of neurons
  3. these pathologies appeared as a result of the disruption of the neurally integrated control ofperistalsis(muscular annular contraction) in those parts where a strong force is necessary to impel the luminalbolusoffeces
  4. idiopathic megacolon and Chagas megacolon appear to have the same cause, namely the degeneration of the myenteric plexus.

WhyT. cruzicauses the destruction, however, remains to be determined. There is evidence for the presence of specificneurotoxinsas well as a disorderlyimmune systemreaction.[citation needed]

Diagnosis[edit]

Diagnosisis achieved mainly by plain and contrastedradiographicalandultrasoundimaging. Colonic marker transit studies are useful to distinguish colonic inertia from functional outlet obstruction causes. In this test, the patient swallows a water-soluble bolus ofradiocontrast agentand films are obtained 1, 3, and 5 days later. Patients with colonic inertia show the marker spread throughout the large intestines, while patients with outlet obstruction exhibit slow accumulations of markers in some places. Acolonoscopycan also be used to rule out mechanical obstructive causes.Anorectal manometrymay help to differentiate acquired from congenital forms. Rectal biopsy is recommended to make a final diagnosis of Hirschsprung disease.[12]

Treatment[edit]

Possible treatments include:[13]

  • Stable cases are effectively treated withlaxativesand bulking agents, as well as modifications indietand stool habits.
  • Corticosteroidsand other anti-inflammatory medications are used in toxic megacolon.
  • Antibioticsare used for bacterial infections such as oralvancomycinforClostridioides difficile
  • Disimpaction of feces and decompression using anorectal and nasogastric tubes are used to treat megacolon.
  • When megacolon worsens and the conservative measures fail to restore transit,surgerymay be necessary.
  • Bethanecholcan also be used to treat megacolon by means of its directcholinergicaction and its stimulation ofmuscarinic receptorswhich bring about aparasympathetic-like effect.

There are several surgical approaches to treat megacolon, such as acolectomy[2][14](removal of the entire colon) with ileorectalanastomosis(ligation of the remaining ileum and rectum segments), or a totalproctocolectomy(removal of colon, sigmoid and rectum) followed byileostomyor followed by ileoanal anastomosis.

See also[edit]

References[edit]

  1. ^"megacolon"atDorland's Medical Dictionary
  2. ^abcdWashabau, Robert J. (2013-01-01), Washabau, Robert J.; Day, Michael J. (eds.),"Chapter 10 - Constipation",Canine and Feline Gastroenterology,Saint Louis: W.B. Saunders, pp. 93–98,doi:10.1016/b978-1-4160-3661-6.00010-9,ISBN978-1-4160-3661-6,retrieved2020-12-21
  3. ^abcMegacolon, ChronicateMedicine
  4. ^abHorton KM, Corl FM, Fishman EK (2000)."CT evaluation of the colon: inflammatory disease".Radiographics.20(2): 399–418.doi:10.1148/radiographics.20.2.g00mc15399.PMID10715339.
  5. ^Porter NH (1961)."Megacolon: a physiological study".Proc. R. Soc. Med.54:1043–7.PMC1870487.PMID14488085.
  6. ^Maull, K. I.; Kinning, W. K.; Kay, S. (January 1982)."Stercoral ulceration".The American Surgeon.48(1): 20–24.PMID7065551.
  7. ^Singer M, Deutschman CS, et al. (February 2016)."The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)".JAMA.315(8): 801–10.doi:10.1001/jama.2016.0287.PMC4968574.PMID26903338.
  8. ^Sweeney AT, Malabanan AO, Blake MA, de las Morenas A, Cachecho R, Melby JC (2000)."Megacolon as the presenting feature in pheochromocytoma".J Clin Endocrinol Metab.85(11): 3968–72.doi:10.1210/jcem.85.11.6947.PMID11095415.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  9. ^Lim DK, Mahendran R (2002)."Risperidone and megacolon"(PDF).Singapore Med J.43(10): 530–2.PMID12587709.
  10. ^Hommes, DW; Sterringa, G; van Deventer, SJ; Tytgat, GN; Weel, J (May 2004)."The pathogenicity of cytomegalovirus in inflammatory bowel disease: a systematic review and evidence-based recommendations for future research".Inflammatory Bowel Diseases.10(3): 245–50.doi:10.1097/00054725-200405000-00011.PMID15290919.S2CID27341787.
  11. ^Koeberle F (1963)."Enteromegaly and cardiomegaly in Chagas disease".Gut.4(4): 399–405.doi:10.1136/gut.4.4.399.PMC1413478.PMID14084752.
  12. ^"Megacolon".The Lecturio Medical Concept Library.Retrieved10 August2021.
  13. ^Szarka LA, Pemberton JH (July 2006)."Treatment of megacolon and megarectum".Curr Treat Options Gastroenterol.9(4): 343–50.doi:10.1007/s11938-006-0016-5.PMID16836953.S2CID38700601.Retrieved10 August2021.
  14. ^Stabile G, Kamm MA, Hawley PR, Lennard-Jones JE (1991)."Colectomy for idiopathic megarectum and megacolon".Gut.32(12): 1538–40.doi:10.1136/gut.32.12.1538.PMC1379258.PMID1773963.

External links[edit]

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