You are in: eMedicine Specialties > Radiology > GASTROINTESTINAL Colitis, IschemicArticle Last Updated: Apr 28, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Muthusamy Chandramohan, MBBS, DMRD, FRCR, Consultant Radiologist, Bradford Teaching Hospitals, UK; Claire Barker, MB, ChB, FRCR, Consulting Radiologist, Christie Hospital, NHS Trust Editors: Neela Lamki, MD, Professor, Department of Radiology, Sultan Qaboos University, Oman; Adjunct Professor, Department of Radiology, Baylor College of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Spencer B Gay, MD, Professor of Radiology, Director of Body Computed Tomography, Department of Radiology, University of Virginia Health Sciences Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Clinical Assistant Professor of Radiology, University of Washington Medical School Author and Editor Disclosure Synonyms and related keywords: reversible vascular occlusion of the colon, mesenteric ischemia, intestinal necrosis, mesenteric thrombosis, mesenteric infarction, transmural infarction, mucosal infarction, mural infarction INTRODUCTIONSection 2 of 11
  BackgroundMarston et al introduced the term ischemic colitis in their article published in 1966.1 This report was preceded by the description of reversible colonic vascular occlusion by Boley and colleagues in 1963.2 Ischemic colitis encompasses a number of clinical entities, all with an end result of insufficient blood supply to a segment or the entire colon. This disease results in ischemic necrosis of varying severities that can range from superficial mucosal involvement to full-thickness transmural necrosis.3 Bowel ischemia is mainly a disease of old age caused by atheroma of mesenteric vessels. Other causes include embolic disease, vasculitis, fibromuscular hyperplasia, aortic aneurysm, blunt abdominal trauma, disseminated intravascular coagulation, irradiation, and hypovolemic or endotoxic shock.4 Occlusive mesenteric infarction (embolus or thrombosis) has a 90% mortality rate, whereas nonocclusive disease has a 10% mortality rate. Venous infarction occurs in young patients, usually after abdominal surgery.5 Patients may present with colicky abdominal pain, which becomes continuous. It may be associated with vomiting, diarrhea, or rectal bleeding.6, 7, 8, 9 For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center and Procedures Center. Also, see eMedicine's patient education articles Colitis, Colonoscopy, and Gastrointestinal Endoscopy. PathophysiologyThe small bowel alone, the colon alone, or occasionally both may sustain a hypoxic injury from a variety of causes.10, 11, 12 Collectively, all these gut hypoxic injuries are designated by the term mesenteric ischemias. Ischemic colitis can be classed as an inflammatory disease of the colon caused by diminished blood flow that leads to bowel wall ischemia and a secondary inflammation. Most of the classifications of intestinal ischemia in the literature are based on the major causative factors. Two mechanisms may cause bowel ischemia: The first and most common is diminished bowel perfusion resulting from low cardiac output; it is often seen in patients with cardiac disease or in patients with prolonged shock of any etiology. The second mechanism is occlusive disease of the vascular supply of bowel resulting from atheroma, thrombosis, or embolism in which the collateral circulation is not adequate to maintain bowel integrity. Regardless of the mechanism, the disease follows the same course. Depending on the cause and severity of the impairment of the bowel blood supply, the morphologic pattern can be arbitrarily subdivided into 3 groups: (1) transmural infarction, (2) mural infarction in which the injury extends from the mucosa into the muscularis, and (3) mucosal infarction in which ischemic damage is confined to the mucosa.13, 14 Causes of mesenteric ischemia include the following:
Related Medscape topics: Transmural infarction Transmural infarction is more common in the small bowel because it is entirely dependent on the mesenteric blood supply, whereas the large bowel is near the posterior abdominal wall, from where it may acquire a collateral blood supply and venous drainage. Transmural infarction usually involves a long segment of bowel, although in rare cases, skip lesions occur. Transmural infarction is usually the result of thrombosis or embolism of the superior mesenteric artery (SMA), which may affect only the small bowel (approximately one half of the mesenteric ischemias). Mesenteric venous thrombosis is another cause; this may involve both the small bowel and the large bowel. Transmural infarction of the small bowel usually involves long segments, but in rare cases, small segments may be involved. Colonic infarction tends to occur in 2 watershed territories: (1) the splenic flexure, which is the watershed territory between the SMA and IMA blood supply, and (2) the distal sigmoid colon, which forms the watershed area between the IMA and hypogastric artery supply. Regardless of whether the ischemia is the result of arterial or venous occlusion, the infarcted bowel always appears hemorrhagic. Early in the course of disease, the bowel appears intensely congested and dusky or purplish red in color, with foci of subserosal and submucosal ecchymoses. As the disease progresses, the bowel wall appears edematous, thickened, rubbery, and hemorrhagic. The lumen of the bowel may contain mucus or frank blood. Arterial occlusion usually results in a sharply defined border between the infarcted bowel and the normal vascularized bowel, whereas in venous thrombosis, the boundary between infarcted bowel is ill defined with no clear demarcation between viable and nonviable bowel. Microscopy reveals suffusion of the bowel wall, which tends to mask the underlying ischemic necrosis. Later in the course of disease, inflammatory infiltration of the bowel wall and ulceration ensue. Bacterial contamination is often present, and bowel perforation may occur within 3-4 days. Arterial occlusion may be difficult to demonstrate histologically, particularly if ischemia is the result of spasm or a low-perfusion state superimposed on atheromatous disease. Mucosal and mural infarction Mucosal and mural infarction is an ischemic injury that is confined to the inner layers of the bowel wall. It is usually the result of hypoperfusion rather than occlusive disease. The hypoxic injury may extend deeply, but the serosa is usually spared. Shock and cardiac failure are major causative factors. Many patients with this condition have also received vasoconstrictor drugs such as digitalis or norepinephrine. This type of injury may involve any part of the gut and is usually patchy and segmental, unlike transmural infarction, which involves long segments. In some cases, minute intramural thrombi are found; whether these are the cause or effect of the ischemic injury is not clear. The involved bowel loops may appear dark red or purple as a result of luminal hemorrhage, but serosal hemorrhage, necrosis, or inflammatory exudate is absent. The mucosa appears hemorrhagic, edematous, and thickened, with superficial ulceration. Histologic analysis may show vascular dilatation associated with a few extravasated red cells and hemorrhagic necrosis within the superficial layers of the mucosa. However, this necrosis may extend into submucosa and the superficial layers of the muscularis. In the colon, bacterial contamination may produce superimposed pseudomembranous inflammation. The combination of necrosis and bacterial invasion develops when the mucosal barrier becomes defective. Thus, the morphologic changes seen in ischemic colitis may resemble those of pseudomembranous colitides or other inflammatory and/or infective processes. FrequencyUnited StatesNo reliable demographic data describe the incidence of ischemic colitis in the United States. The incidence is thought to be underestimated because many mild cases may go unreported. In contrast, the incidence in patients undergoing abdominal aortic reconstructive procedures has been studied. Hunter and Guernsey reported that as many as 10% of such patients have some degree of ischemic colitis.15 With our aging population, the incidence of ischemic colitis is expected to increase. Ischemic colitis is the most common type of ischemic disease affecting the gastrointestinal tract and accounts for 50% of cases. InternationalNo data suggest that the worldwide incidence or prevalence of ischemic colitis differ from that in the United States. Mortality/MorbidityMortality and morbidity depend on the cause and comorbidities, such as underlying cardiac disease and vasculitides, among others. The prognosis for patients with colonic ischemia is more favorable than that seen with other forms of mesenteric ischemia. A transient ischemic episode resolves usually within 1-3 months without sequelae. With significant ischemic injury, long strictures may follow and cause mechanical problems such as bowel obstruction. More severe ischemic trauma may cause bowel gangrene and perforation, but this is rare. The mortality of patients requiring surgery for ischemic colitis remains high because most patients with bowel ischemia have significant comorbidities. Earlier diagnosis and measures to reduce blood loss may contribute to improving the overall outcome.16 RaceNo racial or ethnic predilection for ischemic colitis is reported. SexThe male-to-female ratio in ischemic colitis is approximately 1:1. AgeIschemic colitis is a disease of the elderly. It is rarely seen in those younger than 60 years. The average patient age at diagnosis is 70 years.19 Younger patients can develop ischemic colitis. Most published descriptions have been case reports or small case series. Etiologies have included sickle cell disease, other vasculopathies or coagulopathies, disease induced by drugs (eg, cocaine, oral contraceptives), or long-distance running. AnatomyThe colon derives its blood supply from both the SMA and the IMA (see Image 1). The ileocolic, right colic, and middle colic arteries arising from the SMA supply the ascending and transverse colon up to the splenic flexure. The middle colic artery may occasionally arise from the celiac axis in association with the dorsal pancreatic artery. Therefore, celiac-axis angiography is sometimes necessary to evaluate the colonic blood supply. The IMA arises from the left anterior wall of the lower abdominal aorta at variable levels from the second to the fourth lumbar vertebral bodies. The size of the IMA varies greatly in an adult. The diameter of the artery varies from 1.2-5.5 mm. The same holds true for the branches of the IMA. No relationship exists between the size of the IMA and the degree of atheromatous disease within the aorta or IMA itself. However, a rough relationship is noted between the size of the left colic artery and the length of the colonic segment it supplies: the longer the length supplied, the greater the diameter. The IMA courses parallel to the lower abdominal aorta and gives off its first ascending branch 3-4 cm from its origin. This left colic artery may form a single trunk in 40% of patients. More commonly (60%), the first ascending branch consists of the left colic artery, but it can also give rise to sigmoid branches. The descending branch is a continuation of the IMA, which results in further branches to the sigmoid artery and which then continues as a superior hemorrhoidal artery. The left colic and sigmoid arteries participate via a large anastomotic arcade within the mesocolon known as the marginal artery of Drummond.20 The vasa recta supplying the bowel wall arise from the marginal artery of Drummond and other anastomotic arcades within the mesocolon. The marginal artery provides a link between the branches of the SMA and IMA. In chronic ischemia, this may be in the form of a hypertrophied vessel, the so-called wandering artery of Drummond. Further collateralization between the SMA and IMA occurs through the arch of Riolan. The arcades between the SMA and IMA are commonly seen during clinical angiography because of the frequency of IMA occlusion in the elderly population. The inferior mesenteric vein is a continuation of the superior hemorrhoidal vein. During its upward course, it receives the sigmoid and left colonic veins. The inferior mesenteric vein drains into the splenic vein behind the pancreatic tail. Clinical DetailsThe radiologic appearances of ischemic colitis are nonspecific and may be seen in other inflammatory disorders of the colon. A reliable diagnosis of ischemic colitis can be made only when the radiologic findings are correlated with the clinical results. With sudden thromboembolism, patients experience abdominal pain localized to the left side of the abdomen, along with tenderness and bloody diarrhea. Severe ischemia may lead to bowel necrosis and perforation that results in an acute abdomen and shock. The patient's sign and symptoms generally resolve within several days. In some cases, a bowel stricture may develop and cause bowel obstruction. Rarely, chronic rectal ischemia may occur, causing rectal pain and incontinence.21 Preferred ExaminationAbdominal plain radiography is usually an initial examination undertaken in most cases involving acute abdominal problems. Although the initial radiographic findings may be normal in colonic ischemia, it is an invaluable procedure in the differential diagnosis of an acute abdomen.22 Barium enema results are abnormal in 90% of patients with ischemic colitis. CT is the single best test after plain radiography because it can exclude many other causes of abdominal pain and can also establish the diagnosis of intestinal ischemia. MRI is mostly useful for magnetic resonance angiography, particularly in individuals with compromised renal function. Ultrasonography is a noninvasive technique that may provide useful information, particularly in investigating chronic mesenteric ischemia. It is unlikely to be conclusive in excluding mesenteric ischemia. Angiography has a limited role in cases of colonic ischemia, but it may be invaluable in a few specific indications, such as arteriovenous fistulas and vascular steal syndrome. Limitations of TechniquesThe radiologic features of ischemic colitis are nonspecific and may be seen in other inflammatory disorders of the colon. Results with all modalities may be normal in patients with established ischemic colitis. DIFFERENTIALSSection 3 of 11
Adrenal Adenoma Adrenal Carcinoma Adrenal Hemorrhage Adrenal Metastases RADIOGRAPHSection 4 of 11
FindingsPlain radiographic features include the following:
Findings on barium enema examination may include the following:
Degree of ConfidenceThe plain radiographic findings may be entirely normal, particularly early in the disease. However, the results of barium enema are abnormal in 90% of patients with ischemic colitis. False Positives/NegativesInflammatory bowel disease, infective colitides, and carcinoma may mimic ischemic colitis. The stricture formation in ischemic colonic disease is smooth and tapering, with a concentric lumen and without shouldering or contour defects. Sacculations are common in ischemic colitis, but skip lesions are rare. In inflammatory bowel disease, cobblestoning, skip lesions, and small punched-out ulcers are common features. In colonic carcinoma, the narrowing is eccentric and associated with shouldering. In the early stages, contour defects may be observed. In some cases of ischemic colitis, extensive mucosal ulceration may simulate a lymphosarcoma on a barium enema study. CT SCANSection 5 of 11
FindingsCT has been used as a diagnostic tool in patients with suspected intestinal ischemia. CT not only depicts changes in the blood vessels but also shows changes in the bowel wall, often in association with ancillary abdominal findings. Contrast-enhanced CT also provides information regarding the hemodynamics of blood flow to the bowel (see Images 16-32).23, 24, 25, 26, 27, 28 The specific CT signs for establishing the diagnosis of bowel ischemia depend on the degree of ischemia, the length of bowel loops involved, and whether both the large bowel and small bowel are affected. Findings may include the following:
Degree of ConfidenceCT is regarded as a valuable noninvasive tool in the diagnosis of mesenteric ischemia. Conflicting reports have appeared in the radiology literature regarding the sensitivity of CT in the diagnosis of mesenteric ischemia. Earlier reports showed a poor sensitivity of around 39%. However, more recent reports involving high-quality infusion techniques resulted in a higher sensitivity of 64-82%. This improved sensitivity is partly related to improved detection rates of more specific signs, such as direct visualization of thromboembolism in the mesenteric vessels and the lack of visualization of bowel-wall enhancement. False Positives/NegativesHigh-quality images are usually difficult to acquire because of the poor general condition of these patients. CT appears to be significantly limited in detecting small peripheral mesenteric emboli. Some of the well-known CT features of mesenteric ischemia, such as diffuse bowel dilatation, bowel wall thickening, ascites, mesenteric haziness, and vascular engorgement, are elicited in only 36% of the patients. Some of the CT findings are nonspecific and may be found in inflammatory bowel disease. MRISection 6 of 11
FindingsHa et al showed that the sensitivity of MRI in the detection of bowel ischemia is comparable to that of CT.29 MRI may be useful in depicting bowel-wall changes and in demonstrating mesenteric vascular abnormalities. As with CT, the additional use of contrast enhancement allows an assessment of the dynamic changes in the bowel wall.30 Degree of ConfidenceMRI is as sensitive as CT in the diagnosis of bowel wall ischemia, and it has the added advantage of not using ionizing radiation. Some researchers have attempted cine phase-contrast MRI for the quantitation of mesenteric blood flow.31 They measured blood flow in the SMA 30 minutes after the patient ate a meal and found promising criteria for differentiating healthy patients from those with chronic intestinal ischemia. False Positives/NegativesMRI has significant problems in depicting small thromboembolism in small mesenteric vessels. ULTRASOUNDSection 7 of 11
FindingsBowel gas frequently prevents the visualization of colonic changes, which are usually most marked around the splenic flexure. In the initial stages, the ischemic bowel may show increased peristalsis, which is then reduced. The bowel wall becomes thickened, and nodular and intramural hemorrhage and edema give rise to areas of reduced echogenicity. Echogenic areas may be seen in the bowel wall; these may reflect either areas of infarction infiltrate or clot. Echogenic areas with shadowing occur as a result of intramural gas. Gas may also be detected in the portal vein; this is a poor prognostic sign. Doppler color flow imaging is performed after the patient fasts overnight to minimize bowel gas. The patient is usually scanned in a supine position with the head slightly elevated to allow the abdominal viscera to descend. To identify the celiac axis and the SMA, the aorta is scanned in the sagittal left paramedian plane, starting at the xiphisternum. The SMA is 1-2 cm distal to the celiac axis; however, the 2 may have a common origin. Before Doppler studies of the SMA and celiac axis are performed, a Doppler velocity signal in the aorta is obtained at the level of the celiac axis and the SMA at a 60° angle. The aorta is scanned for atheroma, dissection, and aneurysm. Color flow and spectral analysis are used to detect flow disturbances. The peak systolic aortic velocity is recorded, after which velocity measurements are made at the origins of the celiac axis and the SMA. Care should be taken when recording Doppler time-velocity waveforms at the origins of the celiac axis and the SMA because the insonation angle may be inadvertently increased beyond 60°. Both the celiac axis and the SMA should be examined during both inspiration and expiration to distinguish extrinsic disease (eg, compression of median arcuate ligament of the diaphragm on the celiac axis) from intrinsic disease (atheroma).32, 33 Evaluation of the celiac axis Color flow Doppler sonography is effective in demonstrating flow disturbances associated with tortuosity and stenosis at the origin of the celiac axis. Doppler spectral waveforms in a normal celiac axis after fasting demonstrate a forward flow with an average peak systolic velocity of 123 cm/s ± 9 in persons aged 48-79 years. A significant increase in the systolic or diastolic flow velocity occurs after a meal. This increase is also reflected in the hepatic and splenic arteries. The average postprandial systolic velocity 30 minutes after a meal of 355 K cal is 132 cm/s ± 7. In the presence of a 60% stenosis of the celiac axis, the peak velocity is increased to 167-208 cm/s ± 9. With this degree of stenosis, color Doppler imaging demonstrates a high-velocity jet at the stenotic site associated with poststenotic turbulent flow. The potential for collateralization between the celiac axis, SMA, and IMA is remarkable. As a result, the peak systolic velocity in the celiac axis may be lower or much higher than expected when concomitant SMA occlusion is present. This variation may result in the overestimation or underestimation of the extent of ischemic disease. Evaluation of the SMA After fasting, the SMA has low diastolic flow. However, after a meal, both the peak systolic and end-diastolic velocities are significantly increased if arterial stenosis is absent. The normal fasting SMA velocities are 128 cm/s ± 16 in persons aged 23-42 years. After a meal, the peak systolic velocity increases to 162 cm/s ± 11; the end-diastolic velocity is in the range of 48 cm/s ± 7 within 15 minutes after the meal. The peak systolic velocity almost doubles within 45 minutes after a meal. With significant SMA stenosis, the peak systolic velocity exceeds 270 cm/s, with a concomitant increase in diastolic flow. Color flow Doppler imaging shows a jet through the stenotic segment with turbulent flow downstream, which continues for some distance. Degree of ConfidenceUltrasonography is a sensitive yet noninvasive technique that may provide useful information about mesenteric ischemia. Images may demonstrate absent or barely visible color flow, absent arterial signals, and thickened bowel-wall loops. Doppler techniques are particularly useful for investigating chronic mesenteric ischemia. False Positives/NegativesLimitations of Doppler analysis of celiac artery and SMA ischemia include the following: (1) there is great potential for collateralization in the splanchnic vessels, which may make an assessment of a single-vessel stenosis difficult; (2) the risk of error increases when the angle of insonation is greater than 60°; and (3) careful placement of the sample volume is crucial. The SMA must be examined throughout the visualized vessel; otherwise, a false-negative diagnosis may result. Gas-filled dilated bowel in ileus or small bowel obstruction may prevent adequate visualization of the vasculature. ANGIOGRAPHYSection 8 of 11
FindingsImmediately after an ischemic insult to the colon, the appearance may be normal unless vascular occlusion is present (see Images 11-12). With an increasing colonic inflammatory response, the following may be observed: dilated arteries, prominent accumulation of contrast material in the bowel parenchymal, and dense and early venous filling. The arteriovenous transit time may be accelerated. The venous phase of a superior or inferior mesenteric angiogram may depict small ectatic draining veins. In cases of superior or inferior mesenteric vein thrombosis, the veins may not be visualized, and collateral venous filling may be depicted. Superior or inferior mesenteric arteriovenous fistulas are readily identified with angiography. A vascular steal syndrome is usually diagnosed by means of inferior mesenteric angiography. Degree of ConfidenceAngiography has a limited role in the diagnosis of colonic ischemia; however, for a few specific indications, angiography may be invaluable (see Findings above). False Positives/NegativesIn established colonic ischemia, no angiographic changes may be observed, or the angiographic changes may be indistinguishable from those of inflammatory bowel disease. Also, the severity of the ischemic insult and the angiographic changes appear to be poorly correlated. INTERVENTIONSection 9 of 11
Medical/Legal Pitfalls
See also the Medscape topic Medical Malpractice and Legal Issues. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
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