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General Considerations
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Colonic ischemia, also referred to as ischemic colitis, is the most frequent form of mesenteric ischemia, accounting for 75% of all intestinal ischemia and affecting primarily the elderly. It is estimated that colonic ischemia may account for as many as 3 per 1000 hospital admissions. Findings of colonic ischemia are seen in 1 of every 100 colonoscopies and may be misdiagnosed as inflammatory bowel disease or infectious colitis (Plate 3). Colonic ischemia has been described in several clinical settings (Table 6–2), although in many instances, no specific cause can be identified. Many cases are initially misdiagnosed as inflammatory bowel disease or infectious colitis, especially in individuals younger than age 50 years. The risk of colonic ischemia appears to be highest for patients who have recently undergone cardiovascular surgery, and these patients may experience more severe episodes.
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Ischemic injury to the colon usually occurs as a consequence of a sudden and transient reduction in blood flow, resulting in a low-flow state. In the majority of cases, a specific occluding anatomic lesion cannot be identified. Although it may occur anywhere, colonic ischemia most commonly affects the so-called watershed areas with a limited collateral blood supply, such as the splenic flexure and left colon (Figure 6–7). Ischemia is usually mucosal and rarely transmural; consequently, gangrenous colitis and colonic strictures are infrequent. Eighty-five percent of cases of colonic ischemia resolve spontaneously within 2 weeks.
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Patients with colonic ischemia usually present with abrupt onset of crampy left lower quadrant abdominal pain, and mild to moderate rectal bleeding or bloody diarrhea within the first 24 hours. Over 90% of patients are older than 60 years. Cardiovascular disease is common, and frequent precipitating factors include hypotension, cardiovascular surgery (coronary artery bypass grafting, aortic aneurism repair), dialysis, and dehydration. Physical examination reveals mild to moderate abdominal tenderness over the affected bowel, most often left-sided.
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In contrast to patients with AMI, those with colonic ischemia do not usually appear acutely ill. Bleeding is usually mild, and patients rarely require blood transfusion. Peritoneal signs, if present, would suggest perforation or peritonitis. Ischemic colitis is usually a singular event, and only 5% of patients develop a recurrence.
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The diagnosis is usually established on the basis of clinical history, physical examination, and endoscopic or radiologic studies. Although most patients who develop colonic ischemia are elderly, the condition can also occur in younger patients. For patients who are younger than age 50, several precipitants of colonic ischemia should be considered (see Table 6–2). In young women, the triad of smoking, use of oral contraceptives, and carriage of the factor V Leiden mutation may be associated with increased risk of colonic ischemia. Recent reports indicate that giving penicillin derivatives to patients who harbor Klebsiella oxytoca may precipitate hemorrhagic colitis.
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Diagnostic modalities include flexible sigmoidoscopy or colonoscopy, plain films of the abdomen, and CT scan. Colonoscopy with biopsies makes the definitive diagnosis; however, endoscopy should be avoided in patients with significant abdominal pain or distention because air insufflation may precipitate perforation in cases of severe ischemia. Endoscopic findings frequently include petechial bleeding, pale mucosa, and, in more severe cases, hemorrhagic ulceration (see Plate 3), and biopsy specimens show characteristic findings. Plain films of the abdomen are usually nondiagnostic, but thumbprinting representing submucosal hemorrhage and edema may be seen in 20–25% of cases. The use of plain films has been largely superseded by the ready availability and accuracy of CT scans. CT scans can demonstrate wall thickening, mucosal and submucosal hemorrhage, and pericolic fat stranding, and occasionally bowel wall pneumatosis (Figure 6–8).
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Angiography is usually not necessary in the evaluation of colonic ischemia; however, it should be considered if the clinical findings raise concern for concomitant small bowel ischemia or infarction.
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Stool studies should be performed to exclude infections such as Escherichia coli O157:H7, Campylobacter enteritis, Klebsiella oxytoca, Shigella, or Clostridium difficile, which can be associated with hemorrhagic colitis.
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Patients with colonic ischemia are usually placed on bowel rest. Patients should be followed with serial abdominal examinations and monitored for bleeding, fever, leukocytosis, and electrolyte abnormalities. Although there are no controlled randomized trials proving the effectiveness of antibiotics in reducing morbidity and mortality, broad-spectrum intravenous antibiotics are recommended. Any medications that can cause vasoconstriction and promote ischemia should be withdrawn (ie, digitalis, glycosides, vasopressin, and diuretics). Marked colonic distention is treated with rectal tubes and nasogastric decompression if necessary. There is no role for anticoagulation or corticosteroids. Prognosis is favorable, and most patients improve within a few days and demonstrate clinical and radiologic resolution within 2 weeks.
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Indications for surgery include peritoneal signs suggesting perforation, gangrenous colitis, massive bleeding, toxic megacolon, and recurrent sepsis. Long-term complications, including persistent recurrent colitis and colonic structures, are infrequent but may require resection of the affected colonic segment.
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In contrast to small bowel ischemia, colonic ischemia is rarely life threatening. However, some reports suggest that ischemia of the right colon may have a worse prognosis compared with ischemia of other parts of the colon. Furthermore, the development of colonic ischemia in the setting of recent cardiovascular surgery also deserves special mention, as the natural history of colonic ischemia in these patients may be more severe. Prolonged colonic ischemia, such as can occur in patients with ruptured abdominal aortic aneurysms or prolonged aortic cross-clamp time, can lead to acute gangrenous colitis and transmural infarction of the colon. Although emergent operative intervention may be necessary in the setting of sepsis and peritoneal signs, most cases of colonic ischemia resolve with conservative management.
Brandt LJ, Feuerstadt P, Blaszka MC. Anatomic patterns, patient characteristics, and clinical outcomes in ischemic colitis: a study of 313 cases supported by histology.
Am J Gastroenterol. 2010;105:2245–2252.
[PubMed: 20531399]
Hogenauer C, Langner C, Beubler E, et al. Klebsiella oxytoca as a causative organism of antibiotic-associated hemorrhagic colitis.
N Engl J Med. 2006;355:2418–2426.
[PubMed: 17151365]