Ischemic colitis refers to inflammation of the colon secondary to vascular insufficiency and ischemia. It is sometimes considered under the same spectrum as intestinal ischemia. The severity and consequences of the disease are highly variable.
Ischemic bowel is typically a disease of the elderly (age >60 years) where atherosclerotic disease or low flow states are usually the cause . It is rare in younger individuals, where it is more likely to be related to vasculitis or hypercoagulable states.
Presenting symptoms include abdominal pain and bloody stools. Tenderness may be present particularly on the left side of the abdomen. In cases of isolated right-sided colonic ischemia patients may present with abdominal pain with out hematochezia or melena. In severe cases where necrosis and perforation have occurred the signs and symptoms are those of peritonitis.
Location of the ischemia relates to the anatomy of the mesenteric vessels:
- superior mesenteric artery (SMA): supplies the right colon from the cecum to the splenic flexure
- inferior mesenteric artery (IMA): supplies the left colon from the splenic flexure to the rectum
- watershed areas :
Low flow states and non-occlusive vessel disease are most common and typically lead to ischemic colitis in watershed areas while complete vessel occlusion can produce an involvement of the entire vascular territory, e.g. acute SMA occlusion.
Diminished or absent blood flow leads to bowel wall ischemia and secondary inflammation. Bacterial contamination may produce superimposed pseudomembranous inflammation. If necrosis develops then ulcerations or perforation can occur. Following the acute event, fibrosis may lead to stricture of the bowel lumen. Different pathological outcomes include :
- gangrenous (15-20%)
- non-gangrenous (80-85%):
- non-reversible (chronic colitis, stricture formation)
The causes can be categorized as follows:
- arterial occlusion:
- arterial emboli
- venous thrombosis:
- hypercoagulative states including malignancy and oral contraceptive pill use
- primary mesenteric venous thrombosis
- low flow states:
- congestive heart failure
- cardiac arrhythmias
- sickle cell disease
- radiation therapy
Abdominal radiographs are often normal, but signs include:
- dilatation due to ileus
- 'thumbprinting' due to mucosal edema/hemorrhage
- localized intramural gas (pneumatosis coli) if necrotic
- free intraperitoneal gas if perforated
Contrast enema is abnormal in 90% but is rarely used for diagnostic purposes:
- segmental region of abnormality
- 'thumbprinting' which is classically obliterated by air insufflation
- ulcerations 'serrated mucosa'
- stricture from fibrosis as a late complication of ischemia
Ultrasound is of limited use due to bowel gas but may show:
- luminal thickening of the affected segment with or without stratification
- hypoechoic wall due to edema
- areas of increased echogenicity if hemorrhage
- echogenic foci with shadowing if intramural gas
- reduced peristalsis may be observed
- Doppler imaging of the SMA origin can be useful in assessing for stenoses
Contrast enhanced imaging (ideally with an arterial phase) is the modality of choice. Features include :
- bowel wall findings
- bowel wall thickening (common), usually uniform and segmental, rarely localized and mass-like
- low-density ring of submucosal edema between enhancing mucosa and serosa (target sign)
- bowel dilatation
- pneumatosis coli (uncommon)
- peritoneal/retroperitoneal cavity findings
- pericolic fluid or fat stranding (common)
- peritoneal free fluid and mesenteric edema
- pneumoperitoneum / pneumoretroperitoneum
- vascular findings
- vascular occlusion (superior or inferior mesenteric artery or vein)
- portal and mesenteric venous gas
Secondary findings supportive of an ischemic etiology include the presence of parenchymal ischemia/infarction in other abdominal organs, such as the liver, kidneys, and spleen.
Can show mesenteric artery occlusion if present. Otherwise, angiography may show increased arterial caliber, accelerated arteriovenous transit time and dilated draining veins due to the inflammatory response. In mesenteric venous thrombosis, the veins may not be visualized, and collateral venous filling may be seen .
Increased uptake of Tcm (V) DMSA tracer in the ischemic bowel may be present but is unreliable .
Treatment and prognosis
Mesenteric arterial or venous occlusion can be treated with anticoagulation or thrombolysis, either systemically or locally. Percutaneous vascular intervention in acute mesenteric artery occlusion is often successful and may involve a combination of thrombus aspiration, thrombolysis and arterial stenting . Surgical resection is indicated in cases of peritonitis, perforation, severe sepsis and massive hemorrhage. Symptomatic strictures may also require surgery .
Prognosis is variable :
- resolution without ongoing complications ~50%
- persistent colitis ~20%
- ischemic stricture ~10%
- gangrene or perforation ~20%
Occlusive mesenteric infarction (embolus or thrombosis) has a high mortality rate (~90%) compared to non-occlusive ischemia (~10%).
Imaging differential considerations include: