CLINICAL IMAGING Imaging in Intestinal Ischemic Disorders RICHARD M. GORE,* KIRAN H. THAKRAR,* UDAY K. MEHTA,* JONATHAN BERLIN,* VAHID YAGHMAI, ‡ and GERALDINE M. NEWMARK ‡ *Department of Radiology, Evanston Northwestern Healthcare, Northwestern University Medical School, Evanston, Illinois; and ‡ Department of Radiology, Northwestern Memorial Hospital, Northwestern University Medical School, Chicago, Illinois Intestinal ischemia and infarction are a heterogeneous group of diseases that have as their unifying theme hypoxia of the small bowel and/or colon. The incidence of bowel ischemia is increasing for a number of reasons: the aging of the popula- tion, the ability of intensive care units to salvage critically ill patients, and heightened clinical awareness of these disorders. Improvements in diagnostic imaging techniques have contrib- uted greatly to the earlier diagnosis of intestinal ischemia, which can have a positive influence on patient outcomes. In this review, advances in multidetector computerized tomogra- phy, magnetic resonance, and ultrasound in the detection of intestinal ischemia are highlighted and placed in the context of expeditious patient management. P atients with intestinal ischemic disorders most often present with abdominal pain and other nonspecific symp- toms such as nausea, vomiting, diarrhea, and bloating. The diagnosis of mesenteric ischemia is often one of exclusion after more common possibilities including bowel obstruction, ap- pendicitis, diverticulitis, cholelithiasis, peptic ulcer disease, and gastroenteritis have been excluded. Intestinal ischemia accounts for approximately 1% of patients presenting with acute abdo- men and 0.1% of all hospital admissions. 1–4 Accordingly, a high index of clinical and radiologic suspicion is required to make a timely diagnosis of gut ischemia and infarction. Gastrointestinal tract ischemia can threaten bowel viability with potentially catastrophic consequences including intestinal necrosis and gangrene. 5–12 Dramatic improvements in cross- sectional imaging have the potential to afford earlier and more precise diagnosis, key to reducing morbidity and mortality of this potentially fatal condition. 13–16 Classification of Ischemic Bowel Disease Intestinal ischemic disorders have been classified into several major types 17–19 : (1) acute mesenteric ischemia, which includes the following: superior mesenteric artery embolism (SMAE), 50%; nonocclusive mesenteric ischemia (NOMI), 20% to 30%; superior mesenteric artery thrombosis (SMAT), 15% to 25%; and superior mesenteric vein (SMV) thrombosis, 5%; (2) chronic mesenteric ischemia (intestinal angina); and (3) colonic ischemia (CI), which includes the following: reversible ischemic colopathy, transient ulcerating ischemic colitis, chronic ulcer- ating ischemic colitis, colonic stricture, colonic gangrene, and fulminant universal ischemic colitis. CI is the most common vascular disorder of the gut, followed by acute mesenteric ischemia. 3,17,18 Acute mesen- teric ischemia is associated with compromise of the blood flow in the superior mesenteric artery (SMA) distribution affecting all, or portions of, the small bowel and right colon. In chronic mesenteric ischemia, the splanchnic circulation is insufficient in meeting the functional demands of the gut, but there is no loss of tissue viability. Acute mesenteric ischemia, chronic mesenteric ischemia, and CI have distinct clinical manifestations that require different management strategies. 17,20 The differentiation between these various isch- emic disorders can by made in some patients with the assis- tance of cross-sectional imaging. Diagnostic Imaging Modalities When imaging patients with suspected intestinal isch- emia, a number of features must be scrutinized on all radiologic evaluations (Table 1). Conventional Abdominal Radiographs The majority of patients with intestinal ischemia show nonspecific findings such as intestinal dilatation, gas- less abdomen, a small-bowel pseudo-obstruction pattern, or paralytic ileus. More specific but far less common findings include thumbprinting, in which multiple round smooth soft-tissue densities project into the intestinal lumen as a result of mucosal and submucosal edema and hemorrhage. Specific late signs include pneumatosis intestinalis (Figure 1) and portal venous gas. In most cases of patients with intes- tinal ischemia, however, conventional abdominal radio- graphs are of limited value. 21–23 Barium Studies Barium studies have been replaced by multidetector computerized tomography (MDCT) and to a lesser degree by magnetic resonance (MR) and ultrasound in the clinical setting Abbreviations used in this paper: CI, colonic ischemia; MDCT, mul- tidetector computerized tomography; MR, magnetic resonance; MRA, magnetic resonance angiography; NOMI, nonocclusive mesenteric ischemia; SMA, superior mesenteric artery; SMAE, superior mesenteric artery embolism; SMAT, superior mesenteric artery thrombosis; SMV, superior mesenteric vein. © 2008 by the AGA Institute 1542-3565/08/$34.00 doi:10.1016/j.cgh.2008.05.007 CLINICAL GASTROENTEROLOGY AND HEPATOLOGY 2008;6:849 – 858
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