CT Diagnosis of Acute Mesenteric Ischemia from Various Causes

Transcription

1 Gastrointestinal Imaging Review Furukawa et al. CT Diagnosis of cute Mesenteric Ischemia Gastrointestinal Imaging Review kira Furukawa 1 Shuzo Kanasaki Naoaki Kono Makoto Wakamiya Toyohiko Tanaka Masashi Takahashi Kiyoshi Murata Furukawa, Kanasaki S, Kono N, et al. Keywords: acute mesenteric ischemia, CT, emergency radiology, mesenteric arterial occlusion, mesenteric venous occlusion, nonocclusive mesenteric ischemia, strangulating bowel obstruction DOI: /JR Received pril 29, 2008; accepted after revision July 22, ll authors: Department of Radiology, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga , Japan. ddress correspondence to. Furukawa (akira@belle.shiga-med.ac.jp). CME This article is available for CME credit. See for more information. JR 2009; 192: X/09/ merican Roentgen Ray Society CT Diagnosis of cute Mesenteric Ischemia from Various Causes OBJECTIVE. cute mesenteric ischemia can be caused by various conditions such as arterial occlusion, venous occlusion, strangulating obstruction, and hypoperfusion associated with nonocclusive vascular disease, and the CT findings vary widely depending on the cause and underlying pathophysiology. The aim of this article is to review the CT appearances of acute mesenteric ischemia in various conditions. CONCLUSION. Recognition of characteristic CT appearances and the variations associated with each cause may help in the accurate interpretation of CT in the diagnosis of mesenteric ischemia. cute mesenteric ischemia is a life-threatening condition, with a reported mortality rate of 50 90% [1 3], that requires early diagnosis and treatment. ngiography has been the reference standard imaging examination; however, the role of CT in this setting has expanded with the advent of helical CT scanners [3 9]. In particular, MDCT technology has dramatically improved the performance of CT by allowing rapid volumetric data acquisition to provide increased longitudinal spatial resolution over a large anatomic volume. From the volume data, retrospective thin or thick sections; sagittal, coronal, or curved multiplanar reformatted images; and CT angiograms with 2D or 3D visualization can be obtained. The rapid scanning capability of this technique coupled with IV bolus contrast injection substantially optimizes scan timing to allow both the arterial and venous phases to be imaged. These advantages are helpful in identifying the site, level, and cause of bowel ischemia by showing abnormalities in the bowel wall, mesentery, and mesenteric vessels. With these developments, the ability of CT for diagnosing mesenteric ischemia has recently been reported to have a sensitivity of approximately 90% [3, 10, 11]. It can also provide alternative diagnoses for patients in whom mesenteric ischemia is suspected. cute mesenteric ischemia can be caused by various conditions such as arterial occlusion, venous occlusion, strangulating obstruc- tion, and hypoperfusion associated with nonocclusive vascular disease, and the CT findings vary widely depending on the cause and underlying pathophysiology [1 5, 9]. CT findings of acute mesenteric ischemia should be characterized on the basis of the cause. In addition, the severity of bowel ischemia (i.e., superficial mucosal or transmural bowel wall necrosis), the location (i.e., small or large bowel), and the presence and degree of hemorrhage or subsequent superinfections may affect the CT appearance. In this article, current imaging techniques and CT findings of mesenteric ischemia resulting from various causes are reviewed with their underlying pathophysiology. CT Examination Preparation Oral and rectal administration of contrast material is recommended for accurate CT and assessment of acute bowel ischemia [1]. variety of contrast materials providing positive, neutral, or negative contrast are available. Whether contrast material is indicated should be carefully considered for patients with bowel obstruction; materials containing barium are contraindicated in patients with bowel leak or perforation. However, in the acute state, particularly in patients with life-threatening conditions, indication of trans oral contrast may not be possible or may not be significant because of an adynamic ileus preventing contrast material from moving through the intestine. 408 JR:192, February 2009

2 CT Diagnosis of cute Mesenteric Ischemia Luminal contrast material may be useful in relatively stable patients, and neutral contrast material should be used for the correct assessment of bowel enhancement after IV contrast administration [3, 10, 12]. The use of neutral contrast material is also beneficial in the formation of multiplanar images and in CT angiography because neutral contrast material does not interfere with image quality [3]. Positive contrast material may be advantageous in assessing patients with ischemic colitis by showing thickened bowel wall and revealing the presence of bowel obstruction or in evaluating patients with a contraindication for IV contrast administration. When contrast material is applied, oral administration of ml of luminal contrast material minutes before scanning and rectal administration of ml of luminal contrast material are used [1, 10]. CT Technique CT images are obtained from the dome of the liver to the level of the perineum to cover the entire course of the intestine. With MDCT scanners, a collimation of mm and a detector pitch of are used. Images with a 5- to 7-mm section thickness are usually constructed for image interpretation; however, thinner sections of contiguous 1 2 mm should also be constructed for multiplanar image reformations and CT angiography. Sagittal images are helpful in assessing the origin of the mesenteric arteries and their variations [10]. cquisition of both unenhanced and contrast-enhanced CT scans is always necessary. The role of unenhanced CT is to identify vascular calcification, hyperattenuating intravascular clotting, and intramural hemorrhage; the role of contrast-enhanced CT is to identify thrombi in the mesenteric arteries and veins, abnormal enhancement of the bowel wall, and the presence of embolism or infarction of other organs [1]. For contrast-enhanced CT, ml of iodinated contrast material is administered at a rate of 2 5 ml/s, and scanning starts with delay times of 30 and 60 seconds for dual acquisition and seconds for single acquisition [1, 10, 13]. CT Findings in cute Bowel Ischemia cute bowel ischemia provides various morphologic and attenuation abnormalities on CT images in the bowel wall, mesenteric vessels, and mesentery. The lumen of the bowel may dilate when filled with air or fluid. These variations depend on the pathogenesis of bowel ischemia as well as the acuteness, duration, site, and extent of the ischemic attack and the state of the collateral circulation. Superimposed bowel wall infection and the presence of perforation may also affect the CT appearances of acute bowel ischemia. In film interpretation, radiologists should assess the bowel wall, its thickness and attenuation; luminal dilatation; mesenteric vessels; mesentery; and other organs [1, 14, 15]. Bowel Wall Bowel wall thickness Normal bowel ranges from 3 to 5 mm thick depending on the degree of bowel distention [1, 14 16]. Bowel wall thickening is not a specific but is the most frequently observed CT finding in mesenteric ischemia and is caused by mural edema, hemorrhage, or superinfection of the ischemic bowel wall [1, 10, 17] (Fig. 1). The degree of thickening is usually less than 1.5 cm, typically 8 9 mm [10], and is often observed in mesenteric venous occlusion, strangulation, ischemic colitis, and mesenteric arterial occlusion after reperfusion [1, 4 6, 10]. In exclusively arterial occlusive mesenteric ischemia or infarction, however, the bowel wall becomes thinner rather than thicker because there is no arterial flow and neither mural edema nor hemorrhage occurs. Thinning of the bowel wall or paper-thin wall is caused by volume loss of tissue and vessels in the bowel wall and by loss of intestinal muscular tone [1, 4 6, 8, 10] (Fig. 2). Bowel wall thickening is not a consistent CT finding in mesenteric ischemia, and the degree of thickening does not correlate with severity [1]. Bowel wall attenuation Bowel wall attenuation should always be assessed on both unenhanced and contrast-enhanced CT images to avoid misinterpretation of high density of the bowel wall as normal positive enhancement on contrast-enhanced CT in cases of intramural hemorrhage. On unenhanced CT images, low attenuation of the bowel wall indicates bowel wall edema, which typically occurs in mesenteric arterial occlusion after reperfusion, mesenteric venous occlusion, strangulation, and ischemic colitis [1, 14 16, 18]. High attenuation of the wall is caused by intramural hemorrhage Fig. 1 Contrast-enhanced CT image of abdomen in 40-year-old woman with superior mesenteric vein and portal vein thrombosis. Wall thickening of ascending and transverse colon (arrowheads) is shown. Engorgement of mesenteric veins is also visible. Fig. 2 Contrast-enhanced CT image of abdomen in 78-year-old man with embolism of superior mesenteric artery. Bowel loops are distended with air and their wall is paper-thin. JR:192, February

3 Furukawa et al. Fig. 3 CT image of lower abdomen in patient with strangulating obstruction. Bowel wall of involved segment is thickened and shows increased density (circle) indicating hemorrhagic infarction. Involved mesentery shows high attenuation. (Reprinted with permission from [32]) and hemorrhagic infarction [1, 14 16, 18] (Fig. 3). On contrast-enhanced CT, a highly specific but not sensitive finding for acute mesenteric ischemia is absent or diminished contrast enhancement of the bowel wall [1, 6, 19]. halo or target appearance is also indicative of mesenteric ischemia, representing hyperemia and hyperperfusion associated with surrounding mural edema, and can be seen in arterial occlusion after reperfusion, nonocclusive and venoocclusive bowel ischemia, strangulation, and ischemic colitis [1, 14 16, 20] (Fig. 4). lthough it seems paradoxical, hyperenhancement of the bowel wall caused by hyperemia (mesenteric venous occlusion), hyperperfusion (reperfusion after arterial occlusive or nonocclusive bowel ischemia), or prolonged enhancement due to reduction of arterial perfusion and venous outflow (strangulating bowel obstruction, nonocclusive bowel ischemia, shock bowel) may be observed in cases of mesenteric ischemia [1, 10] (Fig. 5). Pneumatosis intestinalis can be indicated when CT depicts air in the bowel wall (Fig. 6). In the setting of mesenteric ischemia, pneumatosis often indicates transmural infarction, particularly if it is associated with portomesenteric venous gas [1, 10, 21 23]. Dilatation of the Bowel Lumen The bowel lumen is often dilated because of interruption of normal bowel peristalsis (adynamic ileus) [1, 10]. Fluid distention of Fig. 5 Contrastenhanced CT image of lower abdomen obtained at equilibrium phase in patient with strangulating obstruction. Prominent mural enhancement of affected bowel segment (arrowhead) is shown, which indicates presence of bowel ischemia. (Reprinted with permission from [32]) the bowel loops occurs by increased intestinal secretions, typically in venoocclusive ischemia and strangulating bowel obstruction. In exclusive arterial occlusion, the bowel seldom contains a large amount of luminal fluid [5]. Mesenteric Vessels In most cases, emboli or thrombi in the mesenteric arteries and veins are clearly shown on contrast-enhanced CT images (Figs. 7 and 8); CT angiography may be helpful in seeing them [11]. Engorgement of the mesenteric veins caused by congestion of venous outflow is typically seen in venoocclusive bowel ischemia or strangulating bowel obstruction [1, 4, 5] (Fig. 8). Fig. 4 Contrast-enhanced coronal CT image of pelvis in patient with strangulating obstruction. Bowel wall of involved loop shows target appearance (arrow). Mesentery Mesenteric fat stranding and ascites appear with transudation of fluid in the mesentery or the peritoneal cavity caused by elevation of mesenteric venous pressure, which is commonly seen in strangulating bowel obstruction and venoocclusive bowel ischemia [1, 4, 5]. It is also frequently seen in ischemic colitis because of superinfection of ischemic colonic segments. Therefore, mesenteric fat stranding in these conditions can appear without bowel infarction and has limited value in estimating the severity of bowel ischemia. On the other hand, in patients with arterial occlusive mesenteric ischemia, because the CT finding of fat stranding is almost 410 JR:192, February 2009

4 CT Diagnosis of cute Mesenteric Ischemia exclusively present with transmural infarction, this finding can be helpful in estimating the severity of bowel ischemia [1, 4, 5]. Bowel Ischemia and Infarction in Various Conditions Bowel ischemia and infarction can be caused by various conditions such as mesenteric arterial occlusion, mesenteric venous occlusion, strangulating bowel obstruction, and hypoperfusion associated with nonocclusive vascular disease. The clinical features and typical CT appearances of each condition are summarized in Table 1. cute Mesenteric rterial Occlusion cute mesenteric arterial occlusion is typically caused by a thromboembolism associated with cardiovascular problems followed by arterial thrombosis, which accounts for C Fig year-old man with mesenteric infarction. C, Contrast-enhanced CT images of upper (), mid (B), and lower (C) abdomen show gas in portal venous branches (), gas in mesenteric veins (circle, B), and gas in bowel wall (arrowheads, C) % (arterial embolism, 40 50%; arterial thrombosis, 20 30%) of all acute bowel ischemia cases [1 3, 24 26]. Most emboli wedge at branching points around or distal to the middle colic artery, whereas thrombosis typically occurs at or near the origin of the mesenteric arteries [3]. lthough the severity may vary, bowel ischemia is typically followed by infarction, perforation, and peritonitis unless reperfusion occurs. On contrast-enhanced CT images, emboli and thrombi can be seen as defects in the superior mesenteric artery and its branches [2, 10] (Figs. 7 and 9). The diameter of the superior mesenteric artery is often larger than that of the superior mesenteric vein. The thickness of the bowel wall of the involved segments is the same as or thinner than that of the healthy segments unless reperfusion occurs [1, 4, 9]. The lumen of the bowel may be filled with fluid, gas, or both; however, the bowel seldom contains a large amount of fluid. Contrast enhancement of the involved bowel is absent or diminished [1 5, 9, 10] (Fig. 9). Pneumatosis can typically be observed in cases with transmural infarction with or without associated portomesenteric venous gas. In cases with reperfusion or rich collaterals, the involved bowel segments may thicken and show the halo or target pattern of contrast enhancement [1, 4, 9] (Fig. 10). Coexisting embolism of other organs may also be observed on contrast-enhanced CT, which supports the diagnosis of mesenteric ischemia (Fig. 11). The diagnosis of acute mesenteric arterial occlusion is usually made based on a combination of the CT findings described earlier. The diagnostic performance of CT for mesenteric ischemia confined to mesenteric arterial occlusion has not been ascertained, to our knowledge; however, the diagnostic performance of CT for primary mesenteric ischemia, including arterial and venous occlusive and nonocclusive mesenteric ischemia, has been reported as 64 96% in sensitivity and % in specificity [6, 11]. In the case of each CT finding, a lack of focal bowel wall enhancement and the presence of pneumatosis intestinalis are relatively sensitive (sensitivity, 42%) and highly specific (specificity, %) [11]. Findings of defects or occlusion of the mesenteric arteries or veins and gas in the mesenteric or portal veins or in the mesenteric arteries are less sensitive (12 15%) but are highly specific (94 100%) [11]. Findings of bowel wall thickening and mesenteric stranding are relatively high in sensitivity (85 88%) but are less specific (61 72%) [11]. B JR:192, February

5 Furukawa et al. Fig. 7 Contrast-enhanced CT image in patient with embolism of superior mesenteric artery shows defect (arrowhead) in superior mesenteric artery. Venous Occlusion Thrombosis of the mesenteric vein can be primary or secondary to portal hypertension or infection or can be associated with various hypercoagulopathy states [1, 2, 20, 27]. Mesenteric venous obstruction does not typically lead to severe bowel ischemia; however, thrombosis of the mesenteric vein, particularly at a distal level, may cause bowel infarction and accounts for 5 10% of acute bowel ischemia. Impairment of venous drainage causes elevation of the hydrostatic pressure, which leads to extravascular leakage of plasma, RBCs, or both into the bowel wall, mesentery, and peritoneal cavity. The bowel loops are typically prominently dilated [1, 3, 26]. Impairment of venous drainage may also compromise the arterial blood flow and cause bowel ischemia and infarction. On contrast-enhanced CT, thrombus in the mesenteric and portal veins is usually visible, and mesenteric venous obstruction can be confirmed by CT in more than 90% of cases [28 30] (Fig. 12). Engorgement of the mesenteric veins is also observed. Fat stranding in the mesentery and ascites are common TBLE 1: Clinical Features and Typical CT Findings of Mesenteric Ischemia in Various Conditions findings. The bowel wall is prominently thickened with absent or diminished enhancement, hyperenhancement, or a halo or target pattern of contrast enhancement [1 5, 7, 28]. bsent or diminished contrast enhancement of the bowel wall usually indicates transmural infarction, particularly when it is associated with pneumatosis and portomesenteric venous gas [28 30]. On the contrary, the degree of bowel wall thickening, mesenteric fat stranding, or ascites does not correlate with the severity of ischemic bowel damage [28]. Characteristic rterial Occlusion Venous Occlusion Strangulation Nonocclusion Incidence 60 70% of PMI 5 10% of PMI 10% of SBO 20% of PMI Presentation cute Subacute cute cute or subacute Risk factors Bowel wall ttenuation of bowel wall on unenhanced CT Enhancement of bowel wall on contrast-enhanced CT rrhythmia, myocardial infarction, valve disease, atherosclerosis a, prolonged hypotension a Thinning, no change, or thickening with reperfusion Not characteristic Diminished, absent, target appearance or high with reperfusion Portal hypertension, venous hypercoagulopathy, right-sided heart failure Previous abdominal surgery, internal and external hernia, intestinal malrotation Hypovolemia, hypotension, low cardiac output, digoxin, α-adrenergic agonists Thickening Thickening No change or thickening with reperfusion Low with edema; high with hemorrhage Diminished, absent, target appearance, or increased Low with edema; high with hemorrhage Diminished, absent, target appearance, or increased Not characteristic Diminished, absent, heterogeneous in distribution Bowel dilatation Not apparent Moderate to prominent Prominent (filled with fluid) Not apparent Mesenteric vessels Defect or defects in arteries, arterial occlusion, SM > SMV in diameter Defect or defects in veins, venous engorgement No defect, venous engorgement No defect, arterial constriction Mesentery Not hazy until mesenteric infarction occurs Hazy with ascites Fig. 8 Contrast-enhanced CT image in 40-year-old man (same patient as Fig. 2) with superior mesenteric vein thrombosis shows defect in superior mesenteric vein (arrowhead). Distal branches of vein are engorged. Hazy with ascites, whirl sign [44], or spoke wheel sign [45] Not hazy until mesenteric infarction occurs Note PMI = primary mesenteric ischemia (i.e., arterial or venous occlusive or nonocclusive bowel ischemia), SBO = small-bowel obstruction, SM = superior mesenteric artery, SMV = superior mesenteric vein. a risk factor for thrombosis. 412 JR:192, February 2009

6 CT Diagnosis of cute Mesenteric Ischemia Fig year-old woman with superior mesenteric artery embolism., Contrast-enhanced CT image obtained cephalad to B shows defect in superior mesenteric artery (arrowhead). B, Contrast-enhanced CT image shows that mural enhancement is absent at most intestinal loops. Fig. 10 Contrast-enhanced CT image in 83-year-old woman with superior mesenteric artery embolism after reperfusion. Mural thickening of intestine (circle) is visible, showing target appearance. Fig. 11 Contrast-enhanced CT image in 74-year-old man with superior mesenteric artery embolism shows defect (arrowhead) in superior mesenteric artery. In addition, contrast enhancement of right kidney (arrow) is absent, which indicates embolism of right renal artery. B Fig year-old man with superior mesenteric vein thrombosis., Contrast-enhanced CT image obtained cephalad to B shows thrombi in superior mesenteric vein (arrowhead) and splenic vein (arrow). B, Contrast-enhanced CT image shows engorgement of mesenteric veins (arrowhead) and mural thickening of intestine. scites is present. B JR:192, February

7 Furukawa et al. Fig. 13 Illustration of closed-loop obstruction. Closed-loop obstruction is unique form of mechanical bowel obstruction in which two points of intestine along its course are obstructed at single site. rrowhead shows site of obstruction. C = closed loop, P = proximal loop, D = distal loop. Strangulating Obstruction: Closed-Loop Bowel Obstruction Strangulating obstruction is a mechanical bowel obstruction associated with bowel ischemia that is seen in approximately 10% of patients with small-bowel obstruction [31, 32]. Strangulating obstruction is almost exclusively associated with a closed-loop obstruction (Figs. 13 and 14), which is caused most often by an adhesive band and occasionally by an internal or external hernia. closed-loop obstruction tends to involve the mesentery and mesenteric vessels and is prone to produce a volvulus. Typically, strangulation in a closed-loop bowel obstruction is caused initially by impairment of venous Fig. 14 Example of closed-loop obstruction. xial MR image in 52-year-old woman shows site of obstruction (arrowhead), closed loop (C), proximal loop (P), and distal loop (D). outflow followed by arterial ischemia because the arterial pressure is higher than the venous pressure. Congestion or hemorrhage in the bowel wall and mesentery occurs, and the affected bowel loops are distended and filled with fluid. On CT, a closed-loop obstruction is identified by a unique configuration of C- or U- Fig. 15 Contrast-enhanced CT image shows closed-loop obstruction at right lower abdomen. Distended loops are seen filled with fluid and mesentery is converging toward site of obstruction (circle). Bowel wall is slightly thickened and density of mesentery is increased. (Reprinted with permission from [31]) Fig. 16 Contrast-enhanced coronal CT image shows closed-loop obstruction at lower abdomen. Distended loops are seen around their mesentery. Contrast enhancement is absent at bowel loops on right-hand side (arrowheads) and attached mesentery shows increased density, which indicates mesenteric ischemia. 414 JR:192, February 2009

8 CT Diagnosis of cute Mesenteric Ischemia Fig. 17 Contrast-enhanced CT image () of pelvis in 69-year-old man with nonocclusive mesenteric ischemia. Contrast enhancement is prominently diminished or absent at distal ileal loops (arrowheads). Bowel wall thickening is not present. fter reperfusion, bowel loops show prominent wall thickening with appearance of target sign (B). shaped distended loops with the mesenteric vessels converging toward the site of obstruction (Figs ). The obstructed site of the closed loops can be located by following the course of the distended bowel loops [31 35]. The affected bowel is filled almost exclusively with only fluid and no gas. The affected mesentery typically shows a fan shape. In cases with strangulation, the bowel wall is thickened and shows absent or diminished enhancement, hyperenhancement, or a halo or target pattern of enhancement on contrastenhanced CT examination. The affected mesentery shows infiltration and stranding associated with engorged mesenteric veins. scites is also observed [31 35]. CT performance in diagnosing strangulation is reported as % in sensitivity, 61 93% in specificity, 72 88% in positive predictive value, and % in negative predictive value [36 39], although a relatively low sensitivity of 51.9% has been reported recently [40]. The diagnosis of strangulation is based on the characteristic findings described earlier or their combination. mong those findings, absent or diminished bowel wall enhancement and infiltration of the affected mesentery are highly specific. The small-bowel feces sign is also reported as a useful finding indicating the presence of strangulation [40]. Hypoperfusion ssociated with Nonocclusive Vascular Disease Bowel ischemia and infarction can occur with a reduction of mesenteric blood supply without vascular occlusion, which is called nonocclusive mesenteric ischemia or infarction. This type of bowel ischemia accounts for 20 30% of all acute mesenteric ischemia or infarction cases, with mortality rates from 30% to 93% [3, 41, 42]. reduction of the mesenteric blood supply is the result of mesenteric arterial vasoconstriction on reflex to hypotension or administration or abuse of digitalis, ergotamine, vasopressin or other vasoconstrictive agents, amphetamine, and cocaine [3, 7, 41, 42]. Ischemic injury may range from reversible superficial damage localized to the watershed areas to a more severe form that extends to the entire bowel. Hypoperfusion results in increased vascular permeability that leads to extravascular leakage of plasma, RBCs, or both into the bowel wall, mesentery, and peritoneal cavity. Shock bowel is a variation of nonocclusive mesenteric ischemia caused by hypotensive shock induced by blunt abdominal trauma [3, 43]. Ischemic colitis and obstructive colitis are considered similar disease entities [1, 4, 5]. On CT, the bowel wall of the involved segments may be normal or thickened (Fig. 17). The pattern of enhancement is variable as absent or diminished enhancement, increased enhancement, or halo or target type of enhancement [1, 4, 5]. Fat stranding of the mesentery and ascites are visible. mong various conditions of mesenteric ischemia, nonocclusive mesenteric ischemia is the most difficult condition to diagnose on CT, and angiography is often required for correct and confident diagnosis [42]. Conclusion n accurate and early diagnosis is essential for the appropriate and successful treatment of patients with acute mesenteric ischemia to improve their prognoses. With the advances in CT technology, CT has realized a high diagnostic performance and become an essential diagnostic tool in this clinical setting. For a correct diagnosis, a technically appropriate CT examination and proper interpretation of images are mandatory. Because acute mesenteric ischemia can be caused by various conditions, the CT findings vary widely, depending on the cause and underlying patho physiology and the presence of associated complications. Recognition of the characteristic CT appearances and variations of each cause may help in the accurate interpretation of CT in the diagnosis of mesenteric ischemia. cknowledgments We thank Tsutomu Sakamoto, Katsumi Hayakawa, and Masato Fujita for their instruction and assistance with the manuscript. References 1. Wiesner W, Khurana B, Ji H, Ros PR. CT of acute bowel ischemia. Radiology 2003; 226: Oldenburg W, Lau LL, Rondenburg TL, Edmonds HJ, Burger CD. cute mesenteric ischemia. rch Intern Med 2004; 164: Segatto E, Mortelé KJ, Ji H, Wiesner W, Ros PR. cute small bowel ischemia: CT imaging findings. Semin Ultrasound CT MR 2003; 24: Chou CK, Mark CW, Tzeng WS, Chang JM. CT of small bowel ischemia. bdom Imaging 2004; B JR:192, February

9 Furukawa et al. 29: Chou CK. CT manifestations of bowel ischemia. JR 2002; 178: Taourel PG, Deneuville M, Pradel J, Régent D, Bruel JM. cute mesenteric ischemia: diagnosis with contrast-enhanced CT. Radiology 1996; 199: Rha SE, Ha HK, Le SH, et al. CT and MR imaging findings of bowel ischemia from various primary causes. RadioGraphics 2000; 20: Hoton KM, Fishman EK. Multi-detector row CT of mesenteric ischemia: can it be done? Radio- Graphics 2001; 21: Levy D. Mesenteric ischemia. Radiol Clin North m 2007; 45: Horton KM, Fishman EK. Multidetector CT angiography in the diagnosis of mesenteric ischemia. Radiol Clin North m 2007; 45: Kirkpatrick ID, Kroeker M, Greenberg HM. Biphasic CT with mesenteric CT angiography in the evaluation of acute mesenteric ischemia: initial experience. Radiology 2003; 229: Megibow IJ, Babb JS, Hecht EM, et al. Evaluation of bowel distention and bowel wall appearance by using neutral oral contrast agent for multi-detector row CT. Radiology 2005; 238: Schindera ST, Nelson RC, DeLong DM, et al. Multi-detector row CT of the small bowel: peak enhancement temporal window initial experience. Radiology 2007; 243: Macari M, Balthazar EJ. CT of bowel wall thickening: significance and pitfalls of interpretation. JR 2001; 176: Macari M, Megibow J, Balthazar EJ. pattern approach to the abnormal small bowel: observations at MDCT and CT enterography. JR 2007; 188: Wittenberg J, Harisinghani MG, Jhaveri K, Varghese J, Mueller PR. lgorithmic approach to CT diagnosis of the abnormal bowel wall. Radio- Graphics 2002; 22: Lee R, Tung HK, Tung PH, Cheung SC, Chan FL. CT in acute mesenteric ischemia. Clin Radiol 2003; 58: Bertnicke BJ, Balfe DM. CT appearance of intestinal ischemia and intramural hemorrhage. Radiol Clin North m 1994; 32: Klein HM, Lensing R, Klosterhalfen B, Toens C, Guenther RW. Diagnostic imaging of mesenteric infarction. Radiology 1995; 197: Ha HK, Rha SE, Kim Y, uh YH. CT and MR diagnosis of intestinal ischemia. Semin Ultrasound CT MR 2000; 21: Wiesner W, Mortelé KJ, Glickman JN, Ji H, Ros PR. Pneumatosis intestinalis and portomesenteric venous gas in intestinal ischemia: correlation of CT findings with severity of ischemia and clinical outcome. JR 2001; 177: Kernagis LY, Levine MS, Jacobs JE. Pneumatosis intestinalis in patients with ischemia: correlation of CT findings with viability of the bowel. JR 2003; 180: Ho LM, Paulson EK, Thompson WM. Pneumatosis intestinalis in the adult: benign to life-threatening causes. JR 2007; 188: Bradbury W, Erittenden J, McBride K, Ruckley CV. Mesenteric ischemia: a multidisciplinary approach. Br J Surg 1995; 82: Mansour M. Management of acute mesenteric ischemia. rch Surg 1999; 134: Stoney RJ, Cunningham CG. cute mesenteric ischemia. Surgery 1993; 114: Grendel JH, Ockner RK. Mesenteric venous thrombosis. Gastroenterology 1982; 82: Bradbury MS, Kavanagh PV, Bechtold RE, et al. Mesenteric venous thrombosis: diagnosis and noninvasive imaging. RadioGraphics 2002; 22: Rhee RY, Gloviczki P. Mesenteric venous thrombosis. Surg Clin North m 1997; 77: Harward TR, Green D, Bergan JJ, Rizzo RJ, Yao JS. Mesenteric venous thrombosis. J Vasc Surg 1989; 9: Furukawa, Yamasaki M, Furuichi K, et al. Helical CT in the diagnosis of small bowel obstruction. RadioGraphics 2001; 21: Furukawa, Yamasaki M, Takahashi M, et al. CT diagnosis of small bowel obstruction: scanning technique, interpretation and role in the diagnosis. Semin Ultrasound CT MR 2003; 24: Frager DH, Baer JW. Role of CT in evaluating patients with small-bowel obstruction. Semin Ultrasound CT MR 1995; 16: Balthazar EJ. George W. Holmes Lecture: CT of small-bowel obstruction. JR 1994; 162: Balthazar EJ, Birnbaum B, Megibow J, Gordon RB, Whelan C, Hulnick DH. Closed-loop and strangulating intestinal obstruction: CT signs. Radiology 1992; 185: Zalcman M, Sy M, Donckier V, Closset J, Gansbeke DV. Helical CT signs in the diagnosis of intestinal ischemia small-bowel obstruction. JR 2000; 175: Frager D, Baer JW, Medwid SW, Rothpearl, Bossart P. Detection of intestinal ischemia in patients with acute small-bowel obstruction due to adhesions or hernia: efficacy of CT. JR 1996; 166: Balthazar EJ, Liebeskind ME, Macari M. Intestinal ischemia in patients in whom small bowel obstruction is suspected: evaluation of accuracy, limitations, and clinical implications of CT in diagnosis. Radiology 1997; 205: Ha HK, Kim JS, Lee MS, et al. Differentiation of simple and strangulated small-bowel obstructions: usefulness of known CT criteria. Radiology 1997; 204: Sheedy SP, Earnest IVF, Fletcher JC, Fidler JL, Hoskin TL. CT of small-bowel ischemia associated with obstruction in emergency department patients: diagnostic performance evaluation. Radiology 2006; 241: Clotz S, Vestring T, Rötker J, Schmidt C, Scheld HH, Schmid C. Diagnosis and treatment of nonocclusive mesenteric ischemia after open heart surgery. nn Thorac Surg 2001; 72: Trompeter M, Brazda T, Remy CT, Vestring T, Reimer P. Non-occlusive mesenteric ischemia: etiology, diagnosis, and interventional therapy. Eur Radiol 2002; 12: Kim Y, Ha HK. Evaluation of suspected mesenteric ischemia: efficacy of radiologic studies. Radiol Clin North m 2003; 41: Khurana B. The whirl sign. Radiology 2003; 226: Rudloff U. The spoke wheel sign: bowel. Radiology 2005; 237: FOR YOUR INFORMTION This article is available for CME credit. See for more information. 416 JR:192, February 2009