MDCT in Ischemic colitis: how to define the etiology and acute, subacute and chronic phase of damage in the emergency setting

Colon Ischemia (CI) is the most common vascular disorder of gastrointestinal tract with a reported incidence of 6.1-44 cases/100000 person-years with confirmatory histopathology. However, the true incidence of CI poses some difficulty, and even vigilant clinicians with high-risk patients often miss the diagnosis since clinical presentation is nonspecific or could have mild transient nature. Detection of CI results crucial to plan the correct therapeutic approach and reduce the reported mortality rate (4-12%). Diagnosis of CI is based on a combination of clinical suspicion, radiological, endoscopic, and histological findings. Some AA consider colonoscopy as diagnostic test of choice, however a preparation is required and it is not without risk, above all in severely ill patients. There are two types of colonic insult: ischaemic and reperfusive. The first one occurs above all during ischaemic/non-occlusive mesenteric ischemia; in this case the colonic wall appears thinned with dilated lumen and fluid in paracolic space appears. When reperfusion occurs the large bowel wall appears thickened and stratified, because of subepithelial edema and/or hemorrhage, with consequent lumen caliber reduction. Shaggy contour of the involved intestine and misty mesentery are associated to the pericolic fluid. The pericolic fluid results a crucial finding for CI diagnosis: in fact, in case of ischemic CI, dilated thinned colonic wall could be misdiagnosed as a physiological colonic distension caused by the presence of intestinal gas, whereas, in case of reperfused CI, the thickening of large bowel wall is an unspecific condition, similar to malignant or inflammatory diseases. Moreover pericolic fluid may increase or decrease depending on the evolution of the ischemic damage suggesting the decision of a medical or surgical treatment. Radiologists should not forget the hypothesis of CI, being aware that MDCT could be sufficient to suggest the diagnosis of the IC, allowing for early identification and grading definition, and in a short term follow-up, discriminating patients who need urgent surgery from patients in which a medical treatment and follow-up and can be proposed.