You are in: eMedicine Specialties > Radiology > GASTROINTESTINAL Mesenteric IschemiaArticle Last Updated: May 30, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Mohammad Alobaidi, MD, Diagnostic Radiologist, River Oaks Imaging and Diagnostics, Spencer Radiology Mohammad Alobaidi is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, and Texas Medical Association Coauthor(s): Syed Zh Jafri, MD, FACR, Clinical Associate Professor of Radiology, Wayne State University School of Medicine; Chief, Section of Body CT, William Beaumont Hospital Editors: Zahir Amin, MD, MBBS, MRCP, FRCR, Consulting Staff, Department of Imaging, University College Hospital, UK; 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, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related keywords: bowel infarction, bowel ischemia, intestinal angina, ischemic colitis, bowel necrosis, bowel ischemia INTRODUCTIONSection 2 of 12
  BackgroundMesenteric ischemia is characterized by inadequate blood flow to or from the involved mesenteric vessels supplying a particular segment of bowel. The organs typically affected are the small bowel or colon. The source of blood that is lacking can be arterial or venous, and hemodynamically, the cause can be occlusive or nonocclusive. Mesenteric ischemia can be acute or chronic. The diagnosis of mesenteric ischemia often is a challenge to both clinicians and radiologists. Patients with inflammatory bowel disease and infectious colitis can present with similar physical signs and symptoms, including cramping abdominal pain, diarrhea, leukocytosis, and hematochezia. Bowel wall thickening is a finding common to all 3 types of disease; however, the pattern of vascular distribution can sometimes narrow the differential diagnosis. PathophysiologyThe etiologies of mesenteric ischemia are many. Arterial causes account for most cases and include atheromatous plaque formations with the development of intimal calcifications, embolic phenomena from cardiac disease, abdominal aortic aneurysms with dissection into the superior mesenteric artery (SMA), and hypoperfusion secondary to hypovolemic shock or low-flow cardiac failure. Chronic arterial disease results from atherosclerosis, fibromuscular dysplasia, and vasculitis. Both occlusive and nonocclusive subtypes can occur; however, occlusive disease is more frequent than nonocclusive disease in the acute setting. The SMA and the inferior mesenteric artery (IMA), including corresponding smaller colic and intestinal branches, typically are involved more frequently than the celiac artery. Venous causes of mesenteric ischemia are encountered less frequently. In these cases, bowel ischemia results from decreased mesenteric outflow of deoxygenated blood rather than from decreased perfusion of oxygen-rich blood. The particular cause of venous ischemia in a patient often is not clear. Predisposing risk factors are associated with thrombosis and include recent abdominal surgery, infection, and hypercoagulable states. Mortality rates in this subset of patients generally are low. The superior mesenteric vein (SMV) is involved more often than the inferior mesenteric vein (IMV). Additional rare causes of mesenteric ischemia include small bowel herniation, adhesions, intussusception, and, rarely, antiphospholipid antibody syndrome (APS). APS is associated with hypercoagulable states secondary to circulating immunoglobulins that interact with phospholipids in cell membranes. The 2 known circulating immunoglobulin antibodies are anticardiolipin antibody and lupus anticoagulant antibody. These 2 entities have been linked to deep venous thrombosis, cerebrovascular accidents, and recurrent spontaneous abortions. APS also has been shown to be associated with abdominal vascular thrombosis and ischemia. In a recent study by Kaushik et al, 13 (31%) of 42 patients with APS had CT findings of bowel ischemia.1 Large or smaller segments of bowel may be involved, depending on the location of the occlusion. The underlying mechanisms of injury are identical whether the source is complete occlusion or hypoperfusion. With diminishing blood flow, the susceptible bowel mucosal layer becomes anoxic, leading to cell fragility and irreversible cell death. Eventually, the mucosa becomes edematous and inflamed and begins to slough and ulcerate. Then, the patient experiences malabsorption, which causes diarrhea and rectal bleeding. If collateral circulation is adequate, perfusion may be restored with resultant fibrosis. FrequencyInternationalMesenteric ischemia can have many causes and presents with a wide variety of clinical and radiologic findings. Arterial sources far outnumber venous sources by a ratio of approximately 9 to 1. Similarly, arterial occlusive disease occurs more frequently than nonocclusive disease by a ratio of approximately 9 to 1. Mortality/MorbidityThe major cause of mortality in patients with mesenteric ischemia is bowel necrosis. Mortality from all causes is as high as 70%. However, several factors (particularly, the adequacy of collateral vessels) account for variability in mortality rates in different patient populations. RaceNo race predilection is known. SexNo sex predilection is known. AgeMost patients who develop mesenteric ischemia are older than 50 years. Venous causes tend to affect a wider range of patients. Clinical DetailsThe evaluation of patients who present to the emergency department with an acute abdomen is often a challenge. Symptoms are usually nonspecific and may be confused with other causes of abdominal pain, including diverticulitis, appendicitis, Crohn disease, peptic ulcer disease, and pelvic inflammatory disease. Classic acute mesenteric ischemia presents with acute abdominal pain that initially is characterized as cramping pain, followed by a continuous dull pain. Unlike diverticulitis and appendicitis, in which the pain is typically in the lower quadrants, the pain in mesenteric ischemia is usually more diffuse. However, depending on the particular segment involved, the pain may be more localized to one side of the abdomen. Ischemic pain that involves the SMA tends to be more diffuse because both the small bowel and the right colon may be involved, corresponding to the vascular territory. Ischemic pain toward the left side more often involves the distribution of the IMA. However, if only small contributing arterial branches are involved, such as the right colic branch, the pain may be located on the right. As ischemia progresses, mucosal sloughing and necrosis ensue. Bloody diarrhea, gross bleeding per rectum, and/or leukocytosis are delayed manifestations. In addition, diagnostic symptoms may be further confused if peritoneal signs resulting from bowel infarction and necrosis are noted. Patients with chronic mesenteric ischemic disease present with postprandial abdominal pain, typically within several minutes of a meal. These patients typically are aware of the precipitating events that lead to the symptoms and, thus, are reluctant to eat, as with patients who have peptic ulcer disease. Symptoms correspond to the chronicity of disease and include weight loss and chronic diarrhea from malabsorption. Preferred ExaminationPertinent history and a physical examination can narrow the differential diagnosis in patients with an acute abdomen, particularly when considering the timing of the event, localizing signs and symptoms, and vascular distribution of the pain. Unless the patient is unstable, imaging is the criterion standard for diagnosis.
Limitations of Techniques
DIFFERENTIALSSection 3 of 12
Appendicitis Bowel, Trauma Colitis, Pseudomembranous Colon, Adenocarcinoma Colon, Diverticulitis Crohn Disease Necrotizing Enterocolitis Pneumatosis Intestinalis Typhlitis Ulcerative Colitis RADIOGRAPHSection 4 of 12
FindingsPlain radiographic findings are often normal. Although upright and supine abdominal images are helpful screening tools for detecting free air or bowel obstruction, the findings are usually not specific for mesenteric ischemia. Findings such as thumbprinting (mucosal edema) are occasionally masked by a gasless fluid-filled abdomen. With barium enema examination, a decreased and irregular bowel lumen is seen. When free air, bowel obstruction, or thumbprinting is apparent, plain radiographic findings are often sensitive but not specific for the disease because many other forms of bowel disease can exhibit similar findings. Other plain radiographic findings include pneumatosis; this represents luminal gas that has dissected into the bowel wall, which is seen in less than 30% of patients. Peripherally located portal venous gas in the right or left upper quadrant is a rare finding on plain radiographs that strongly suggests mesenteric ischemia. Degree of ConfidenceMesenteric ischemia is rarely, if ever, diagnosed by using plain abdominal images. Because the disease is a continuum, normal findings on abdominal radiographs should not mislead the interpreter to exclude the disease. The diagnosis often requires the use of additional imaging modalities. False Positives/NegativesA finding of thumbprinting on plain radiographs is not specific for mesenteric ischemia. Other causes of colonic or small-bowel-wall thickening include ulcerative colitis and lymphoma infiltration. Lymphoma infiltration often mimics focal small-vessel mesenteric ischemia, particularly in the cecum and small bowel. Diffuse wall thickening commonly results from ulcerative colitis. Diagnosis of these entities has different clinical implications, since the treatment options differ. Therefore, the role of plain radiographs in mesenteric ischemia should be solely to screen for bowel perforation or obstruction. Less frequent findings, such as wall thickening or portal venous gas, are occasionally depicted on plain radiographs; however, their absence should not exclude ischemia. CT SCANSection 5 of 12
FindingsCT is the primary imaging modality, and it has been proven to be highly accurate in the diagnosis of mesenteric ischemia; scans sometimes depict the underlying etiology. Typically, CT scans show mesenteric edema with irregular thickening of the wall of the small or large bowel that is greater than 3 mm. Large-vessel disease (SMA/SMV, IMA/IMV) is diffuse, whereas small-vessel arterial or venous disease is more likely to be focal. Several causes of ischemia exist.
Degree of ConfidenceRegardless of the cause, mesenteric ischemia produces findings that may mimic those of other inflammatory or infectious conditions. Wall thickening is the most common sign; however, the vascular territory of involvement is not always clear. This limitation reduces the interpreter's degree of confidence regarding the exact etiology. In addition, ischemic colitis can involve both the SMA and IMA in rare cases, producing wall thickening of the left and right colon. False Positives/NegativesThe presence of ulcerative colitis can lead to a false-positive diagnosis of mesenteric ischemia, particularly if the sigmoid and descending segments of the colon are involved. This type of ulcerative colitis simulates ischemia caused from IMA occlusion. Ulcerative colitis involves the rectum in more than 90% of patients because the process progresses in a retrograde fashion. However, in ischemic colitis, the rectum is spared. A false-negative diagnosis of mesenteric ischemia can result from many causes. Focal wall thickening, particularly of the cecum, can be confusing. Tumor infiltration, especially that due to lymphoma and adenocarcinoma, can mimic focal ischemic colitis caused by small colic branches of the SMA. Local lymph node enlargement may be present in infectious and neoplastic processes, allowing them to be further differentiated from ischemia. MRISection 6 of 12
FindingsMagnetic resonance arteriography (MRA) is occasionally used to evaluate the patency of the SMA and IMA. However, MRI plays a limited role in the diagnosis of mesenteric ischemia of the small or large bowel. Typically, if additional imaging modalities are needed, ultrasound or angiography is the next step in the workup. ULTRASOUNDSection 7 of 12
FindingsColor Doppler and spectral waveform ultrasonography help in evaluating the patency and adequacy of flow through the celiac artery, SMA, and IMA. Preprandial and postprandial Doppler examinations are typically performed. Sample velocities are assessed proximal to the stenosis, where flow is expected to be normal; at the stenosis, where velocity is maximal; and distal to the stenosis, where velocity is the most turbulent. The normal response to a meal is an increase in blood flow through the mesenteric circulation, which is measured as the peak systolic arterial flow. Stenosis or occlusion decreases normal laminar blood flow. The severity of the stenosis in the sampled artery is best correlated with the maximum peak systolic velocity. A luminal stenosis of greater than 60-70% is usually considered severe. In response to eating, the peak systolic velocity should increase as arterioles dilate to supply the bowel segment. Published reports of highly predictive values of stenosis include a fasting peak systolic velocity of more than 275 cm/s in the SMA or 200 cm/s in the celiac artery. The normal postprandial peak systolic velocity should increase by approximately 20% or more. An abnormal postprandial response is interpreted as an increase in the peak systolic velocity of less than 20%, which is a blunted response. Another useful parameter is the end-diastolic velocity of the sampled artery during the compliant diastolic cardiac state. The normal end diastolic velocity should increase in the postprandial state, since compliance is greater in this phase of the cardiac and systemic cycle. With stenosis, the end diastolic velocity should decrease secondary to decreased compliance. Degree of ConfidenceAfter a meal, the peak systolic velocity does not always increase, even in patients symptomatic for mesenteric ischemia. Occlusions in the distal branches do not correlate well with postprandial velocities if sampled proximally in the larger vessels. Additionally, the velocities and ratios used to determine the percentage of stenosis are only estimates, and these are operator dependent. False Positives/NegativesSources of error are related to the cause of the ischemia. Abnormal increases in velocity in response to meals are not specific for the diagnosis of ischemia. The findings of significant abnormalities of the celiac artery and SMA on Doppler sonograms do not necessarily indicate mesenteric ischemia. Additionally, Doppler ultrasonography is not useful in evaluating mesenteric ischemia caused by venous abnormalities. Normal findings on an arterial Doppler sonogram in a symptomatic patient do not exclude venous mesenteric ischemia. NUCLEAR MEDICINESection 8 of 12
FindingsNuclear medicine studies are used infrequently in the evaluation of patients with mesenteric ischemia. ANGIOGRAPHYSection 9 of 12
FindingsAngiography is the criterion standard for revealing the site of arterial occlusion of a diseased bowel segment. Images may depict attenuation, vasoconstriction, or complete arterial occlusion of the involved vessel. Degree of ConfidenceAngiographic findings are highly sensitive for vascular narrowing or stenosis when the ischemia is arterial in origin. The finding of veno-occlusive disease is less sensitive in the diagnosis of mesenteric ischemia. False Positives/NegativesAn inherent limitation of angiography is failure to demonstrate nonocclusive disease secondary to hypovolemia or low-output cardiac failure. However, vasospasm as a cause of nonocclusive mesenteric ischemia may occasionally be diagnosed by using angiography. INTERVENTIONSection 10 of 12
The treatment of acute occlusive mesenteric ischemia is usually surgical resection of the infarcted bowel segment. Chronic mesenteric ischemia resulting from poor collateral circulation is not a surgical emergency and may be treated conservatively. Nonocclusive mesenteric ischemia usually is treated nonsurgically. Depending on the cause, direct arterial vasodilatation can be used to improve bowel perfusion. Medical/Legal Pitfalls
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REFERENCESSection 12 of 12
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