You are in: eMedicine Specialties > Radiology > GASTROINTESTINAL Toxic MegacolonArticle Last Updated: Apr 29, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Hemalatha Chandramohan, MBBS, Staff Physician, Department of Geriatric Medicine, Stepping Hill Hospital, United Kingdom Editors: Neela Lamki, MD, Professor, Department of Radiology, Sultan Qaboos University, Oman; Adjunct Professor, Department of Radiology, Baylor College of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; David Andrew Nicholson, BM, BS, FRCR, Honorary Lecturer, Department of Radiology, University of Manchester; Consultant Gastrointestinal Radiologist, Department of Radiology, Hope Hospital, Salford Royal Hospital NHS Trust; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Clinical Assistant Professor of Radiology, University of Washington Medical School Author and Editor Disclosure Synonyms and related keywords: severe colitis, segmental dilatation of the colon, total dilatation of the colon, ulcerative colitis, pancolitis, acute transmural fulminant colitis, Crohn disease, Crohn's disease, antibiotic-induced pseudomembranous colitis, amebiasis, Salmonella enteritis, S enteritis, Campylobacter enteritis, C enteritis, ischemic colitis INTRODUCTIONSection 2 of 9
  BackgroundToxic megacolon is defined as a severe episode of colitis with segmental or total dilatation of the colon. It is typically a complication of ulcerative colitis, but it may be a complication of Crohn disease, antibiotic-related pseudomembranous colitis, and other colitides. Pathologically, acute fulminant colitis is associated with neuromuscular degeneration and a rapid and extensive colonic dilatation. The diagnosis of toxic megacolon is based on clinical findings, simple laboratory results, and a careful scrutiny of the plain abdominal radiograph. Usually, no other radiologic investigations are required. Once toxic megacolon is diagnosed, the patient must be immediately admitted to an intensive care unit where he or she can be monitored by intensivists and a team of physicians and surgeons. The mortality rate is high, at 20%. PathophysiologyMegacolon may occur acutely or as a chronic illness.1 Acute megacolon that occurs in association with severe inflammation of the colon is known as toxic megacolon, whereas acute megacolon without obvious colonic disease is known as Ogilvie's syndrome. Methotrexate, vincristine, and high-dose therapy with autologous stem-cell transplantation for amyloidosis-induced toxic megacolon have also been reported.6 The colon is a frequent site of gastrointestinal complications in patients with HIV infection; these colonic disorders increase in frequency as the immunodeficiency worsens. The most common manifestations of colonic disease in AIDS are diarrhea, lower gastrointestinal bleeding, and abdominal pain; however, toxic megacolon has also been reported. Toxic megacolon almost always occurs in the setting of pancolitis, although the rectum may be spared. Megacolon is considered to be present if the diameter of the colon is 5.5 cm or more, with apparent edema of the bowel wall on plain abdominal radiographs. Rarely, the toxic dilatation may extend to the terminal ileum. Colonic dilatation may be superimposed on an acute fulminant colitis in a patient with a history of inflammatory bowel disease. The dilatation may fluctuate or resolve completely, leaving the patient with toxic colitis. Clostridium difficile is the most common causative agent implicated in pseudomembranous colitis.7, 8, 9 Toxic megacolon secondary to infective colitis is rare in children, but when it occurs, it may be fulminating and potentially fatal. The mortality rate is 15%, and 15% of children require surgery. The course of the disease can be divided into 3 stages: the acute toxic stage, the gut-failure stage, and the convalescence or deterioration stage. Bacterial and/or endotoxin translocation is believed to play an important role in gut failure. Toxic megacolon is associated with an acute transmural fulminant colitis with the neurogenic loss of motor tone. The result is the rapid development of colonic dilatation resulting from damage to the entire wall of the colon associated with neuromuscular degeneration. Histologic examination reveals extensive sloughing of the mucosa and frequent necrosis of the muscle layers of the bowel wall. Thinning of the muscle layer of the colon often occurs. FrequencyUnited StatesTo the author's knowledge, no reliable demographic data describe the incidence of toxic megacolon as a complication of ulcerative colitis and other colitides. InternationalTo the author's knowledge, no data suggest that the worldwide incidence or prevalence of toxic megacolon differs from that in the United States. Mortality/MorbidityToxic megacolon is a fulminating and potentially lethal complication of severe colitis. The disease requires intensive treatment and has a prolonged convalescence period. The mortality rate is 20% in adults and 15% in children. RaceNo racial predilection is noted. SexNo sex preponderance is reported. AgeMost cases affect young adults, but individuals of any age can be affected. Toxic megacolon secondary to infective colitis is rare in children, but when it occurs, it may be fulminating and potentially fatal. Clinical DetailsToxic megacolon is a clinical diagnosis, one based on thorough history taking and physical examination and supported by plain abdominal radiographic findings. Patients have abdominal distention, pain, diarrhea, fever, and dehydration; some patients progress to shock.10 The symptoms may ensue in the setting of known inflammatory bowel disease or antibiotic therapy. In patients receiving steroids, some of the clinical features may be masked. Clinical examination is not accurate in the detection of perforation in the setting of toxic megacolon. The first hint of a colonic perforation may be provided on a plain abdominal radiograph.11, 12, 13, 14 Preferred ExaminationPatients with toxic megacolon often present in the emergency department as having abdominal distention superimposed on chronic or acute diarrhea. The diagnosis should be considered in all such patients. The diagnosis is usually based on thorough clinical history taking and physical examination combined with plain abdominal radiography. CT has a limited role, although it better depicts the anatomic detail of transmural disease, mesenteric involvement, and intraperitoneal complications of inflammatory bowel disease.15 Ultrasonography and radionuclide studies have a limited role if any.16, 17, 18, 19 Limitations of TechniquesChagas disease, Hirschsprung disease, and intestinal pseudo-obstruction may superficially resemble toxic megacolon on plain radiographs.20, 21 However, because they occur in totally different clinical settings, they are unlikely to be confused with toxic megacolon. DIFFERENTIALSSection 3 of 9
Colitis, Ischemic Colitis, Pseudomembranous Crohn Disease Hirschsprung Disease Ulcerative Colitis Other Problems to Be ConsideredChagas disease
RADIOGRAPHSection 4 of 9
FindingsIf toxic megacolon is clinically suspected, patients are usually followed up with plain abdominal radiography every 12-24 hours, depending on the patient's clinical condition. A single abdominal radiograph may not be sufficient and should be combined with a horizontal-beam radiograph, which may better depict large, dilated bowel loops with fluid levels. Also, abdominal perforation is less likely to be missed (see Images 1-5). Toxic megacolon is almost always a complication of pancolitis, with occasional sparing of the rectum. Therefore, changes such as strictures and mucosal abnormalities may be seen in association with toxic megacolon. Toxic megacolon in the setting of Crohn disease is less common, but the plain radiographic findings of toxic megacolon in ulcerative colitis and those of Crohn disease overlap. However, with Crohn disease, the colonic wall tends to be thicker; thus, a thicker colonic wall in the setting of toxic megacolon in a patient with no previous disease should suggest Crohn disease rather than ulcerative colitis. Marked dilatation is observed in the transverse colon; the upper range of normal for the transverse diameter is 5.5-6.5 cm. This finding has led to the belief that the transverse colon is the area most severely affected. However, if a prone radiograph is obtained, the greatest distention is observed in the ascending colon and descending colon. The apparent prominent involvement simply reflects the movement of the retained gas to the least dependent part of the colon. Serial radiographs may show increasing dilatation of the transverse diameter of the colon. Images may show a coarse, irregular mucosal pattern of the large bowel. This thumbprinting is caused by mucosal edema due to inflammatory infiltration. The normal haustral pattern is absent in the involved segments, and pseudopolyps often extend into the lumen.22 These represent mucosal islands in denuded ulcerated colonic wall in ulcerative colitis. Pneumatosis coli is an occasional finding. If perforation occurs, radiographic signs of a pneumoperitoneum may be apparent on the supine and/or lateral decubitus radiographs.19 Degree of ConfidenceA diagnosis of toxic megacolon can be made fairly confidently by using plain radiography in the appropriate clinical setting, although a series of radiographs may be required. False Positives/NegativesDilatation in toxic megacolon may fluctuate or resolve, leaving the patient with toxic colitis. A perforated large bowel in association with a toxic megacolon may be missed on a plain abdominal radiograph. CT SCANSection 5 of 9
FindingsThe large bowel appears distended, with associated fluid levels. The haustral pattern may show edema. In toxic megacolon associated with ulcerative colitis, the bowel wall may be thin. Intramural air in association with small pericolonic fluid collections may be observed. Extraluminal air may be present if a perforation is present as a complication of toxic megacolon.23 Degree of ConfidenceCT provides better anatomic detail of transmural disease, mesenteric involvement, and intraperitoneal complications of inflammatory bowel disease. Extraluminal air associated with bowel perforation is better seen with CT than with other techniques. False Positives/NegativesNone of the CT findings are specific; they may also be found in severe forms of colitides. NUCLEAR MEDICINESection 6 of 9
FindingsTechnetium-99m hexamethyl-propyleneamine oxime (HMPAO)–labeled WBC scanning can be used as an alternative to colonoscopy to assess the extent and severity of the disease in critically ill patients with ulcerative colitis. This technique decreases the number and severity of complications that may occur in these patients. However, the role of this method of scintigraphy is limited in the diagnosis of toxic megacolon and in the determination of its severity. Degree of ConfidenceThe severity of the disease can be adequately determined by means of 99mTc HMPAO–labeled WBC scintigraphy.24 However, its role in the diagnosis of toxic megacolon has not been determined. False Positives/NegativesFindings with 99mTc HMPAO–labeled scintigraphy are nonspecific, and scans in a variety of inflammations and colitides can show uptake. INTERVENTIONSection 7 of 9
The optimal management of severe colitis requires close collaboration between gastroenterologists, intensivists, and surgeons. All patients with severe colitis need to be hospitalized and treated with intravenous steroids. If significant improvement does not follow within 7-10 days, other therapeutic measures (eg, intravenous cyclosporine therapy, surgery) must be considered.25 When surgery is indicated, total colectomy with ileostomy is the appropriate surgical treatment in most cases.26 In patients with toxic megacolon, early surgical intervention is indicated.27 Toxic megacolon secondary to infective colitis is rare in children, but when it occurs, it may be fulminating and potentially fatal. The mortality rate is 15%, and 15% of children require surgery. Medical/Legal Pitfalls
See also the Medscape topic Medical Malpractice and Legal Issues. MULTIMEDIASection 8 of 9
REFERENCESSection 9 of 9
Article Last Updated: Apr 29, 2008 | ||||||||||||||||||||||||||||||||||||||||||
