Ischemic colitis is the damage to the bowel wall as a result of hypoperfusion. It usually occurs in older patients with atherosclerosis as a result of a thromboembolic event, however it may happen in younger patients due to venous thrombosis or vasoconstriction (hypercoagulable states, medications, cocaine use, marathon runners, infections), and in infants with necrotizing enterocolitis. Intestinal obstruction, shock and vasculitides compromising intestinal blood flow would also result in ischemia.

Ischemia may be acute or chronic, and depending on the size of the vessel involved, ischemic damage may be mucosal, mural (mucosa and submucosa) or transmural (all three bowel wall layers). Most common sites are "watershed areas", such as splenic flexure and transverse colon.

Clinically these patients present with abdominal pain and bleeding. The presence of metabolic acidosis, increased serum lactate and LDH may be helpful but are uncommon in mild ischemia and may not be present in early stages of severe ischemia.

Colonoscopy may show petechial hemorrhages, mucosal edema, erythema, ulcerations and bleeding. In severe ischemia, the mucosa is dusky and cyanotic. Fibrosis, strictures and mucosal granularity may be seen in chronic ischemia.

The overall distribution of the changes is segmental, corresponding to the area supplied by the affected vessel(s). Surface epithelium is most vulnerable because it is supplied by the distal portion of intestinal capillaries. Surface epithelium is necrotic, and pseudomembranes may be seen. Bases of the crypts may remain intact if ischemia is not severe, or may look atrophic, or show regenerative atypia. Lamina propria looks hyalinized. Inflammation is scant or absent. Hemosiderin-laden macrophages may be seen. Fibrosis and strictures may be present in chronic ischemia.

Examination of the blood vessels may be helpful in establishing the etiology. The differential diagnosis includes infections (C. difficile pseudomembranous colitis, enterohemorrhagic E.coli infection), inflammatory bowel disease and NSAID effect.

Treatment is surgical if there is transmural ischemia and perforation, or supportive treatment in less severe cases.