Ischemic colitis overview

# Overview
Ischemic colitis is a medical condition in which inflammation and injury of the large intestine result from inadequate blood supply. Ischemic colitis may be classified on the degree of the histopathological damage in the colonic wall: reversible colopathy (submucosal or intramural bleeding), transient colitis, chronic segmental ischemia, gangrenous colitis, and universal fulminant colitis. Also, based on its clinical course into two types: acute ischemic colitis or chronic ischemic colitis. Ischemic colitis is the result of a sudden, temporary, reduction in blood flow that is insufficient to meet the metabolic demands of the region of colon. Ischemic change will subsequently extend from the mucosa to the serosa. Mucosalinjury will develop in 20 minutes to 1 hour, and transmural infarction occurs within 8 to 16 hours. Reperfusion injury can occur with the release of reactive oxygen species, which cause lipid peroxidation within cell membranes, causing cell necrosis. schemic colitis is characterized by abdominal pain which is out of proportion to physical findings. There is a sudden onset of crampy abdominal pain, diarrhea, and an urge to defecate. The pain is mild, located over the affected bowel, and usually to the left side of the lower abdomen. Mild rectal bleeding can be noticed within 24 hours. The blood may be bright red or maroon mixed with the stools. X-rays are mainly used to check for organ perforation and pneumoperitoneum in ischemic colitis. Other noticable signs on x-ray include colonic thumbprinting from mural thickening, pneumatosis coli, a sign of advanced disease, and dilation or air-fluid levels. Ischemic colitis is usually treated with supportive care. Treatment is determined by its severity and include intravenous fluids, bowel rest, nasogastric tube, and total parenteral nutrition.

# Historical Perspective
In 1963, Boley et al first described ischemic colitis in animal studies as vascular occlusion of the colon. In 1966, Marston et al coined the term ischemic colitis.

# Classification
Ischemic colitis may be classified on the degree of the histopathological damage in the colonic wall: reversible colopathy (submucosal or intramural bleeding), transient colitis, chronic segmental ischemia, gangrenous colitis, and universal fulminant colitis. Also, based on its clinical course into two types: acute ischemic colitis or chronic ischemic colitis.

# Pathophysiology
Ischemic colitis is the result of a sudden, temporary, reduction in blood flow that is insufficient to meet the metabolic demands of the region of colon. Ischemic change will subsequently extend from the mucosa to the serosa. Mucosalinjury will develop in 20 minutes to 1 hour, and transmural infarction occurs within 8 to 16 hours. Reperfusion injury can occur with the release of reactive oxygen species, which cause lipid peroxidation within cell membranes, causing cell necrosis.

# Causes
Ischemic colitis causes of reduced blood flow can include changes in the systemic circulation such as low blood pressure or local factors such as constriction of blood vessels, a blood clot, or drugs. In most cases, no specific cause can be identified.

# Differentiating Ischemic Colitis from other Diseases
Ischemic colitis must be differentiated from the many other causes of abdominal pain, rectal bleeding, and diarrhea such as 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.

# Epidemiology and Demographics
Ischemic colitis occurs with greater frequency in the elderly, and is the most common form of bowel ischemia. Ischemic colitis is responsible for about 50 out of 100,000 hospital admissions, and is seen on about 100 in 100,000 endoscopies.

# Risk factors
Risk factors associated with ischemic colitis are cardiovascular and pulmonary diseases such as atherosclerosis and atrial fibrillation, gastrointestinal disease like diarrhea, surgical history and medications.

# Screening
There is insufficient evidence to recommend routine screening for ischemic colitis.

# Natural History, Complications and Prognosis
Ischemic colitis can span a wide spectrum of severity. Majority of patients are treated supportively and recover fully, while a minority with very severe ischemia may develop sepsis and become critically ill. Most patients make a full recovery. As the disease progresses, submucosal hemorrhage or edema may result in focal mucosal thickening, known as thumbprinting. Pneumatosis intestinalis may occur if mucosal damage has taken place with passage of gasinto the bowel wall. Occasionally, after severe ischemia, patients may develop long-term complications such as a stricture or chronic colitis.

# Diagnosis

## History and Symptoms
Ischemic colitis is characterized by abdominal pain which is out of proportion to physical findings. There is a sudden onset of crampy abdominal pain, diarrhea, and an urge to defecate. The pain is mild, located over the affected bowel, and usually to the left side of the lower abdomen. Mild rectal bleeding can be noticed within 24 hours. The blood may be bright red or maroon mixed with the stools.

## Physical Examination
Ischemic colitis is characterized by abdominal pain which is out of proportion to physical findings, specifically excruciating abdominal pain despite limited focal tenderness.

## Laboratory Findings
There are no specific blood tests for ischemic colitis, but an elevated white blood cell count may be present. Other laboratory findings in ischemic colitis include electrolyte and renal abnormalities secondary to dehydration, metabolic acidosis, and lactate level may be elevated due to any tissue hypoxia.

## Abdominal X Ray
Among patients with ischemic colitis, the plain X-rays are often normal or show non-specific findings. X-rays are mainly used to check for organ perforation and pneumoperitoneum in ischemic colitis. Other noticable signs on x-ray include colonic thumbprinting from mural thickening, pneumatosis coli, a sign of advanced disease, and dilation or air-fluid levels.

## CT
Among patients with ischemic colitis, the CT scan shows mild to moderate diffuse bowel wall thickening and marked hyperenhancement of the mucosa.

## MRI
Magnetic resonance imaging (MRI) findings in ischemic colitis of colonic pneumatosis and portomesenteric venous gas can be used to predict the presence of transmural colonic infarction.

## Ultrasound
In ischemic colitis ultrasound has limited use because of bowel gas, but may show luminal thickening over the affected segment and hypoechoic wall due to edema. Limited use due to overlying bowel gas, operator-dependent quality, and poor sensitivity for low flow vessel disease.

## Other imaging finding
Fluoroscopy barium studies rarely used in diagnosis of ischemic colitis. Contrast enema is abnormal in 90% of patients but is rarely used for diagnostic purposes. Barium enema should be avoided in cases where there is a suspicion of gangrene or perforation. Also, barium enema makes the later use of angiography or endoscopy more difficult because of residual contrast agent.

## Other Diagnostic studies
Among patients with a suspicion of ischemic colitis, endoscopic evaluation, via colonoscopy or flexible sigmoidoscopy, is the diagnostic procedure of choice if the diagnosis remains unclear after other imaging studies. Colonoscopy is sensitive and allows visualization of colonic mucosa and histological analysis of biopsies. Colonoscopy requires to be performed within 48 hours for diagnosis of ischemic colitis.

# Treatment

## Medical Therapy
Ischemic colitis is usually treated with supportive care. Treatment is determined by its severity and include intravenous fluids, bowel rest, nasogastric tube, and total parenteral nutrition. Patients with colonic dilatation are managed with insertion of a rectal tube or endoscopic decompression. There is no evidence about the role of anticoagulation or antiplatelet therapy. Steroids have not been shown to improve outcomes.

## Surgery
The mainstay of treatment for ischemic colitis is medical therapy. Surgery is usually reserved for patients with either sepsis, persistent fever and leukocytosis, peritoneal irritation, protracted pain, diarrhea or bleeding, protein-losing colopathy for more than 14 days, free intra-abdominal air, or endoscopically-proved extensive gangrene. Laparotomy confirms the diagnosis and all affected bowel is resected. 20% of patients with acute ischemic colitis will require surgery with an associated mortality rate of up to 60%. Ileocolostomy is performed in patients with right-sided ischemic colitis with viable ileum and transverse colon.

## Primary prevention
There are no established measures for the primary prevention of ischemic colitis, but one can prevent the risk factors leading to ischemic colitis by not smoking, exercising regularly, and maintaining a healthy diet.