Ischemic Colitis Imaging

Overview

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.^[1]

Marston et al introduced the term ischemic colitis in their article published in 1966.^[2] This report was preceded by the description of reversible colonic vascular occlusion by Boley and colleagues in 1963.^[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]}

Cocaine-induced ischemic colitis is a recognized entity, and the diagnosis is based on clinical and endoscopic findings. Diagnostic imaging is helpful for evaluating abdominal symptoms, and previous studies have suggested specific sonographic findings in ischemic colitis.^[10]

Elramah et al conducted a case control retrospective study to determine mortality and risk factors for associated bowel ischemia in cocaine users. The study revealed cocaine-related ischemic colitis has a high mortality. The authors’ findings suggest that cocaine-related ischemia should be considered in young patients presenting with acute abdominal pain and/or rectal bleeding with evidence of bowel wall thickening or pneumatosis on either imaging or colonoscopy. The authors went on to propose that testing for cocaine in these patients may help identify patients at high risk of sepsis and death.^[11]

See the images of ischemic colitis below.

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Arterial blood supply to the large bowel shows the potential site of ischemia.

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Double-contrast barium enema study shows a stricture of the proximal descending colon secondary to ischemia.

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Plain abdominal radiograph in a 65-year-old man presenting with acute abdominal pain and the passage of blood per rectum. Note the thumbprinting in th....

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This 63-year-old man had smoked more than 30 cigarettes a day for over 40 years and gave a 3-year history of claudication. Recently, he presented with....

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This is the first image in a series of contrast-enhanced CT scans on a 72-year-old man presenting with acute abdominal pain. Surgery revealed mesenter....

Preferred examination

Abdominal 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.^[12] Barium enema results are abnormal in 90% of patients with ischemic colitis.^{[13, 14, 12, 15, 16]}

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. For patients who present with symptoms of ischemia, CT scan of the abdomen with oral and IV contrast and laboratory testing can be performed.^[17]

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.^{[18, 19, 20]}

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 techniques

The 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. A reliable diagnosis of ischemic colitis can be made only when the radiologic findings are correlated with the clinical results.

For more information, see the Esophagus, Stomach, and Intestine Center and Procedures Center, as well as Colitis, Colonoscopy, and Gastrointestinal Endoscopy.

• References

Radiography

Plain radiographic features include the following:

• Dilatation of a part of the colon may be seen early. The appearance may be not unlike that of ulcerative colitis with mucosal edema (thumbprinting) and pseudopolyp formation (see the images below).

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  Plain abdominal radiograph in a 65-year-old man presenting with acute abdominal pain and the passage of blood per rectum. Note the thumbprinting in th....

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  Left: Plain abdominal radiograph in a 58-year-old man who underwent an upper GI barium study for nonspecific dyspepsia a few days earlier. The patient....

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  Six days later (see the previous image), the clinical condition of the patient deteriorated, with increasing abdominal pain and signs of peritonism. N....

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  Left: Chest radiograph of a 45-year-old woman with mitral valve disease and atrial fibrillation who presented with acute abdominal symptoms. Note the ....

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  Plain supine abdominal radiograph in a 72-year-old man who presented with bloody diarrhea. Note the thumbprinting of the splenic flexure and the entir....

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  Inferior mesenteric angiogram in the same patient as in the previous image shows a stenosis of more than 50% at the origin of the left colic artery as....

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  Postoperative abdominal radiograph in a 26-year-old patient who had stabbed himself, cutting across the jejunum. The injury was repaired on an emergen....

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  Axial contrast-enhanced CT scans of the same patient as in the previous image shows that the superior mesenteric vein is larger than the aorta. Lower ....

   

  

   
• When both the small bowel and the large bowel are affected by ischemic injury, the small bowel may also become dilated with thickening of the valvulae conniventes.
• Over time, the haustra become thickened and edematous, and it contains a large amount of secretions.
• With further edema, the haustral markings disappear completely, and the colon acquires a hoselike appearance.
• Localized pneumatosis coli may be apparent.
• Eventual tubular narrowing and stricturing appear over a long segment.

Findings on barium enema examination may include the following:

• A rapid sequence of events usually occurs over several weeks after an initial ischemic insult. The events can progress from the early stages of spasm and edema to chronic stricture formation.
• Barium enema examination during the acute stage of a vascular insult demonstrates spasm associated with thickening and blunting of the mucosal folds. Multiple mucosal scalloping or thumbprinting are seen along the contours of the bowel. Seen en face, the thumbprints appear as polypoid filling defects (see the images below).

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  Double-contrast barium enema study shows a stricture of the proximal descending colon secondary to ischemia.

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  Erect radiograph obtained after a double-contrast barium enema study shows a stricture at the splenic flexure.

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  Postevacuation image obtained after a barium enema study shows extensive thumbprinting involving the entire colon, secondary to mesenteric ischemia.

   

  

   
• With further progression of mucosal edema, the folds become thickened and ill defined.
• Intraluminal secretions are increased.
• Ulcerations are frequently observed in pathologic specimens of the diseased bowel segment. However, these may not be deep enough to be demonstrable radiologically. With diffuse ulceration, the mucosa may be completely effaced. Ulcers may be seen as a serrated mucosa. Deep ulcers are a late finding.
• During the healing phase, when fibrosis sets in, associated flattening and rigidity of 1 wall may be observed. The antimesenteric border of the colon becomes pleated because of scarring; this may appear as sacculations or pseudodiverticula.
• With a continuing fibrotic process, the affected segment of the large bowel acquires a tubular shape with smooth contours and a concentric lumen.
• The final outcome is usually a long stricture with proximal bowel dilatation. However, when a stricture develops, it is shorter than the original length of the ischemic bowel, as seen radiologically.
• In the stages before fibrosis develops, partial or complete recovery may occur. The ischemic process may be arrested at any of the previously described stages.

Inflammatory 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.

The 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.

• References

Computed Tomography

CT 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 the images below).^{[21, 22, 23, 24, 25, 26]}

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Axial contrast-enhanced CT scans of the same patient as in the previous image shows that the superior mesenteric vein is larger than the aorta. Lower ....

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This is the first image in a series of contrast-enhanced CT scans on a 72-year-old man presenting with acute abdominal pain. Surgery revealed mesenter....

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Second image in a series of enhanced CT scans in the same patient.

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Third image in a series of enhanced CT scans in the same patient.

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Fourth image in a series of enhanced CT scans in the same patient.

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Fifth image in a series of enhanced CT scans in the same patient.

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Sixth image in a series of enhanced CT scans in the same patient.

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Seventh image in a series of enhanced CT scans in the same patient.

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Eighth image in a series of enhanced CT scans in the same patient.

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Ninth image in a series of enhanced CT scans in the same patient.

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Tenth image in a series of enhanced CT scans in the same patient.

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Eleventh image in a series of enhanced CT scans in the same patient.

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Twelfth image in a series of enhanced CT scans in the same patient.

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Thirteenth image in a series of enhanced CT scans in the same patient.

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Fourteenth image in a series of enhanced CT scans in the same patient.

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Fifteenth image in a series of enhanced CT scans in the same patient.

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Sixteenth and last image in a series of enhanced CT scans in the same patient.

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:

• Thromboembolism in the mesenteric vessels
• Intramural or portal venous gas
• Segmental thickening of the bowel wall
• Absence of bowel wall enhancement with contrast-enhanced CT
• Irregular narrowing of the bowel lumen as a result of mucosal edema (thumbprinting)
• Possible bowel dilatation proximal to the ischemic segment of the bowel
• Nonspecific signs of bowel ischemia, including bowel obstruction, mesenteric edema, mesenteric vascular engagement, and ascites

In a study of patients with symptomatic angiography-verified atherosclerotic obstruction of the superior mesenteric artery (SMA) with acute on chronic mesenteric ischemia (AOCMI) (N = 27) or CMI (N = 20), two thirds of AOCMI patients presented with ischemia-specific CT signs (decreased bowel wall enhancement, pneumatosis, or thrombotic SMA clot). However, the authors noted that any intestinal abnormality in CT together with SMA obstruction should raise suspicion of intestinal ischemia. Most patients with AOCMI had unspecific intestinal findings, such as mesenteric fat stranding in up to 96%, bowel lumen dilatation in 93%, and bowel wall thickening in 70%, while only few patients with CMI had such findings (due to chronic ischemic colitis).^[27]

Degree of confidence

CT 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 and negatives

High-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.

• References

Magnetic Resonance Imaging

Ha et al showed that the sensitivity of MRI in the detection of bowel ischemia is comparable to that of CT.^[18] 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.^[19]

In addition to MRI being as sensitive as CT in the diagnosis of bowel wall ischemia, 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.^[20] 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.

Mazzei et al demonstrated that unenhanced MRI was adequate for diagnosis and follow-up of many cases of ischemic colitis.^[28]

MRI has significant problems in depicting small thromboembolism in small mesenteric vessels.

• References

Ultrasonography

Bowel 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 superior mesenteric artery (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).^{[29, 30]}

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 confidence

Ultrasonography 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 and negatives

Limitations of Doppler analysis of celiac artery and SMA ischemia include the following:

• There is great potential for collateralization in the splanchnic vessels, which may make an assessment of a single-vessel stenosis difficult
• The risk of error increases when the angle of insonation is greater than 60°
• 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.

• References

Nuclear Imaging

Stathaki et al evaluated the use of pentavalent techenetium-99m dimercaptosuccinic acid [Tc-99m (V) DMSA] in the diagnosis of ischemic colitis in 14 patients with endoscopically and histologically confirmed ischemic colitis. Tc-99m (V) DMSA scintigraphy was performed within 2 days after colonoscopy, and images were considered positive when an area of increased activity was observed in the region of interest and considered negative when no abnormal tracer uptake was detected. In 3 of the 14 patients, Tc-99m (V) DMSA images showed moderate activity in the bowel. In the other 11 patients, no abnormal tracer uptake was detected in the abdomen and, therefore, the use of Tc-99m (V) DMSA could not be considered successful in the diagnosis of ischemic colitis.^[31]

• References

Angiography

Angiography has a limited role in the diagnosis of colonic ischemia; however, for a few specific indications, angiography may be invaluable. Immediately after an ischemic insult to the colon, the appearance may be normal unless vascular occlusion is present (see the images below). 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.^[32]

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Digital subtracted superior mesenteric angiogram in a 63-year-old woman known to have a hilar cholangiocarcinoma (note the biliary stent) who presente....

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This 63-year-old man had smoked more than 30 cigarettes a day for over 40 years and gave a 3-year history of claudication. Recently, he presented with....

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Normal inferior mesenteric angiogram in a 53-year-old man. (See also the next image.)

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Normal venous phase of an inferior mesenteric angiogram. (See also the previous image.)

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.

In 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.

• References

Author

Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, Consultant Radiologist and Honorary Professor, North Manchester General Hospital Pennine Acute NHS Trust, UK

Disclosure: Nothing to disclose.

Coauthor(s)

Claire Barker, MB, ChB, FRCR, Consultant Radiologist, Christie Hospital NHS Trust, UK

Disclosure: Nothing to disclose.

Muthusamy Chandramohan, MBBS, DMRD, FRCR, Consultant Radiologist, Bradford Teaching Hospitals, UK

Disclosure: Nothing to disclose.

Specialty Editors

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

Spencer B Gay, MD, Professor of Radiology, Department of Radiology and Medical Imaging, University of Virginia School of Medicine

Disclosure: Nothing to disclose.

Chief Editor

Eugene C Lin, MD, Attending Radiologist, Teaching Coordinator for Cardiac Imaging, Radiology Residency Program, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Neela Lamki, MD, FACR, FRCPC, Professor, Department of Radiology, Sultan Qaboos University, Oman; Adjunct Professor, Department of Radiology, Baylor College of Medicine

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, to the development and writing of this article.

References

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