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BENIGN PATHOLOGYBENIGN PATHOLOGYIschemic ColitisIschemic Colitis

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Ischemic Colitis – Introduction

• Ischemic colitis is a medical condition in which inflammation and injury of the large intestine result from inadequate blood supply.

• Ischemic colitis occurs mostly in the elderly and is the most common form of bowel ischemia.

• Causes of reduced blood flow can include changes in the systemic circulation or local factors, such as constriction of blood vessels or a blood clot.

• Ischemic colitis can span a wide spectrum of severity; most patients are treated supportively and recover fully, while a minority with very severe ischemia may develop sepsis and become critically ill.

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Ischemic Colitis

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Ischemic Colitis – Causes and Epidemiology

• Ischemic colitis is responsible for about 1 in 2000 hospital admissions and is seen on about 1 in 100 endoscopies.

• Men and women are affected equally.

• Ischemic colitis is a disease of the elderly, with more than 90% of cases occurring in people over the age of 60.

• Ischemic colitis is often classified according to the underlying cause. – Occlusive ischemia indicates that a blood clot or other

blockage has cut off blood flow to the colon.– Non-occlusive ischemia develops because of low blood

pressure or constriction of the vessels feeding the colon.

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Ischemic Colitis – Causes and Epidemiology

• Occlusive ischemia—

– Mostly the result of a thromboembolism. Commonly, the embolism is caused by atrial fibrillation, valvular

disease, myocardial infarction, or cardiomyopathy.

• Non-occlusive ischemia—– In hemodynamically unstable patients (i.e. shock), the

mesenteric perfusion may be compromised. This condition is commonly asymptomatic and usually

only apparent through a systemic inflammatory response.

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Ischemic Colitis – Pathophysiology

• Colonic blood supply– The colon receives blood from both the superior and

inferior mesenteric arteries. – The blood supply from these two major arteries overlap with

abundant collateral circulation. – There are vascular “weak” points, at the borders of the

territory supplied by each of these arteries. – These watershed areas are most vulnerable to ischemia

when blood flow decreases, as they have the fewest vascular collaterals.

– The rectum receives blood from both the inferior mesenteric artery and the internal iliac arteries.

– The rectum is rarely involved with colonic ischemia due to this dual blood supply.

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Ischemic Colitis – Pathophysiology

• Development of ischemia—

– Under ordinary conditions, the colon receives between 10% and 35% of the total cardiac output.

– If blood flow to the colon drops by more than about 50%, ischemia will develop.

– The arteries feeding the colon are very sensitive to vasoconstrictors.

– As a result, during periods of low blood pressure, the arteries feeding the colon clamp down vigorously.

– A similar process can result from vasoconstricting drugs such as ergotamine, cocaine, or vasopressors.

– This vasoconstriction can result in non-occlusive ischemic colitis.

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Ischemic Colitis – Signs and Symptoms

• Three progressive phases of ischemic colitis have been described:

– A hyperactive phase occurs first, in which the primary symptoms are severe abdominal pain and the passage of bloody stools. Many patients get better and do not progress beyond this phase.

– A paralytic phase can follow if ischemia continues. In this phase, the abdominal pain becomes more widespread, the belly becomes more tender to the touch, and bowel motility decreases, resulting in abdominal bloating, no further bloody stools, and absent bowel sounds on exam.

– Finally, a shock phase can develop as fluids start to leak through the damaged colon lining. This can result in shock and metabolic acidosis with dehydration, low blood pressure, rapid heart rate, and confusion. Patients who progress to this phase are often critically ill and require intensive care.

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Ischemic Colitis – Diagnosis

• Ischemic colitis must be differentiated from the many other causes of abdominal pain and rectal bleeding (for example, infection, inflammatory bowel disease, diverticulosis, or colon cancer).

• It is also important to differentiate ischemic colitis, which often resolves on its own, from the more immediately life-threatening condition of acute mesenteric ischemia of the small bowel.

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Ischemic Colitis – Diagnostic Tests

• There are no specific blood tests for ischemic colitis. The sensitivity of tests among 73 patients was, as follows:

– White blood cell count more than 15,000/mm3 in 20 patients (27%)

– Serum bicarbonate level less than 24 mmol/L in 26 patients (36%).

• Plain X-rays are often normal or show non-specific findings. In a series of 73 patients, plain abdominal radiography was diagnostic in 56%, showing colic distension in 53% and a pneumoperitoneum in 3%.

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Ischemic Colitis – Diagnostic Tests

• CT scans are often used in the evaluation of abdominal pain and rectal bleeding, and may suggest the diagnosis of ischemic colitis, demonstrate complications, or suggest an alternate diagnosis.

• Endoscopic evaluation, via colonoscopy or flexible sigmoidoscopy, is the procedure of choice if the diagnosis remains unclear. Ischemic colitis has a distinctive endoscopic appearance; endoscopy can also facilitate alternate diagnoses such as infection or inflammatory bowel disease. Biopsies can be taken via endoscopy to provide more definitive information.

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Ischemic Colitis - Treatment

• Except in the most severe cases, ischemic colitis is treated with supportive care. IV fluids are given to treat dehydration, and the patient is placed on bowel rest until the symptoms resolve.

• If possible, cardiac function and oxygenation should be optimized to improve oxygen delivery to the ischemic bowel.

• A nasogastric tube may be inserted if an ileus is present.

• If a patient develops worsening symptoms and signs, such as high white blood cell count, fever, worsened abdominal pain, or increased bleeding, he may require surgical intervention, usually consisting of laparotomy and bowel resection.

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Ischemic Colitis – Long-Term Complications

• About 20% of patients with acute ischemic colitis may develop a long-term complication known as chronic ischemic colitis.

• Symptoms can include recurrent infections, bloody diarrhea, weight loss, and chronic abdominal pain.

• Chronic ischemic colitis is often treated with surgical removal of the chronically diseased portion of the bowel.

• A colonic stricture is a band of scar tissue which forms as a result of the ischemic injury and narrows the lumen of the colon.

• If bowel obstruction develops as a result of stricture, surgical resection is the usual treatment, although endoscopic dilatation and stenting have also been employed.

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Ischemic Colitis - Prognosis

• Most patients with ischemic colitis recovery fully, although the prognosis depends on the severity of the ischemia.

• Patients with pre-existing peripheral vascular disease or ischemia of the ascending (right) colon may be at increased risk for complications or death.

• Non-gangrenous ischemic colitis, which comprises the vast

majority of cases, is associated with a mortality rate of approximately 6%.

• The minority of patients, who develop gangrene as a result of colonic ischemia, have a mortality rate of 50-75% even with surgical treatment.