Intestinal Ischemia Versus Intramural Hemorrhage: CT Evaluation

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1 Michael Macari 1 Hersch Chandarana Emil althazar James abb Received March 27, 2002; accepted after revision July 11, ll authors: Department of Radiology, bdominal Imaging Section, Tisch Hospital, New York University Medical Center, 560 First ve., Ste. HW 207, New York, NY ddress correspondence to M. Macari. JR 2003;180: X/03/ merican Roentgen Ray Society Intestinal Ischemia Versus Intramural Hemorrhage: CT Evaluation OJECTIVE. We evaluated the capability of CT to depict findings that allowed differentiation of small-bowel ischemia from intramural hemorrhage. MTERILS ND METHODS. Findings of 35 CT examinations (19 patients with smallbowel ischemia and 16 patients with intramural hemorrhage) were analyzed by two abdominal radiologists for the degree of wall thickening, location and length of involvement (short, 15 cm; medium, cm; or long, >30 cm), presence of hemoperitoneum, and pattern of attenuation. Patency and caliber of the superior mesenteric artery and vein were noted. Diagnosis was confirmed by laboratory findings, clinical parameters, and follow-up examinations, or at surgery. Mann-Whitney U or Fisher s exact test was used to compare the two conditions for the following features: wall thickening, location and length of involvement, presence of hemoperitoneum, and appearance of the target sign. RESULTS. mong the 35 examinations, 18 abnormal segments with intramural hemorrhage and 19 abnormal segments with ischemia were identified. (Two patients with intramural hemorrhage each had two segments involved.) Mean bowel wall thickness was 11.7 mm (range, 4 25 mm) in patients with intramural hemorrhage and 4.0 mm (range, 1 9 mm) in patients with ischemia. Length of involvement was short in 14 segments with intramural hemorrhage and medium in four segments with intramural hemorrhage; none of the segments with intramural hemorrhage had long involvement. mong the segments with ischemia, length of involvement was medium in three and long in 16; none of the ischemic segments had short involvement. Fifteen (94%) of 16 segments with intramural hemorrhage and six (32%) of 19 segments with ischemia had hemoperitoneum. Seven of the 18 segments with intramural hemorrhage and nine of the 19 with ischemia had a target sign. Segments with intramural hemorrhage exhibited a higher statistically significant degree of wall thickening ( p < 0.001), a shorter length of involvement ( p < ), and a higher incidence of hemoperitoneum ( p < 0.001) than did segments with ischemia. The two groups were not statistically different in location of involvement (p = 0.12) or in the incidence of the target sign (p = 0.18). CONCLUSION. lthough some of the CT features overlap, a short segment involvement with wall thickening of 1 cm or greater is typical of intramural hemorrhage; a long segment involvement with wall thickening of less than 1 cm is typical of ischemia. M any conditions can cause acute abdominal pain. The differential diagnosis, both clinically and at imaging, may be challenging. In a large review of patients who presented to an emergency department with acute abdominal pain, neither small-bowel ischemia nor intramural hemorrhage was listed among the common causes of abdominal pain [1]. Yet, as the merican population ages, both of these conditions are being diagnosed more frequently because of the increased prevalence of both atherosclerotic mesenteric vascular disease and anticoagulation therapy [2]. The CT findings of small-bowel intramural hemorrhage and ischemic bowel have been previously reported [2 6]. CT findings of the ischemic small bowel include bowel wall thickening with or without appearance of a target sign, lack of enhancement of the bowel wall, pneumatosis, arterial embolization, or venous thrombosis [3 5]. In patients with intramural hemorrhage, some of the CT findings may be similar to those of the ischemic small bowel, such as homogeneous bowel wall thickening, presence of a target sign on IV contrast-enhanced studies, and highly attenuated ascites [2, 6]. JR:180, January

2 Macari et al. Only a few reports in the literature describe the imaging findings of intramural hemorrhage after administration of IV contrast material [2, 6]. Moreover, to our knowledge, the similarities and differences in the CT appearance between these two conditions have not been previously addressed in a comparative analysis. The purpose of our study was to evaluate whether CT differences between small-bowel intramural hemorrhage and ischemia could be discerned if a pattern approach to interpreting imaging findings was applied. We retrospectively evaluated proven cases of small-bowel intramural hemorrhage and small-bowel ischemia for the degree of mural thickening, length and location of intestinal involvement, presence of hemoperitoneum, and pattern of attenuation in an attempt to determine if contrast-enhanced CT scans can be used to diagnose these two conditions. Materials and Methods Patients computerized search of our CT database was performed for CT scans obtained from January 1998 through October 2001 to identify patients with an imaging diagnosis of small-bowel ischemia or intramural hemorrhage. Cases are entered into the system daily by radiologists at our institution. The CT database runs on FileMaker Pro 5.5 (FileMaker, Santa Clara, C), a program that allows users to access data by entering keywords related to anatomy and pathology. For this study, the anatomic keyword used was small bowel, and the pathologic keyword was either ischemia or hemorrhage. Therefore, the database searched for cases of small-bowel ischemia or small-bowel hemorrhage. Sixty CT examinations with one of these two diagnoses were found to have been performed during the specified time period. Thirty-nine depicted small-bowel ischemia, and 21 depicted small-bowel intramural hemorrhage. Of these 60 cases, 15 were eliminated because oral and IV contrast materials were not used, leaving 45 patients as potential study cases. For our study, we relied on the final clinical diagnosis as opposed to the final imaging diagnosis as proof of either small-bowel hemorrhage or smallbowel ischemia. In 10 of these 45 patients, clinical follow-up data could not be obtained, and these patients were eliminated from the study. Our series included the remaining 35 patients (17 men and 18 women) who underwent contrast-enhanced CT and for whom clinical follow-up information was available. Nineteen patients had intestinal ischemia, eight men and 11 women who ranged in age from 58 to 93 years (mean age, 71 years). Sixteen patients had intramural hemorrhage, nine men and seven women who ranged in age from 52 to 85 years (mean age, 66 years). CT Technique ll CT examinations were performed with HiSpeed dvantage or CT/i scanners (General Electric Medical Systems, Milwaukee, WI). Helical CT data were acquired with either a slice collimation of 7 mm with a reconstruction interval every 6 mm or a slice collimation of 5 mm with a reconstruction interval of 4 mm, a pitch varying between 1.5 and 2.0, 120 kv, and m. Oral administration of 800 ml of barium sulfate suspension (2.1% weight/volume) (Readi-CaT 2; E-Z-EM, Westbury, NY) or diluted (2%) water-soluble contrast material (Gastrografin [meglumine diatrizoate]; ristol-meyers Squibb, Wallingford, CT) was begun approximately 1 hr before scanning, with the patients ingesting the contrast medium in small increments. Then, 150 ml of nonionic IV contrast material (Ultravist [iopromide], 300 mg I/mL; erlex Laboratories, Wayne, NJ) was administered at a rate of 2 ml/sec via a 22-gauge catheter inserted into an antecubital vein using a power injector (Envision CT injector; Medrad, Pittsburgh, P). Image Interpretation The 35 CT examinations were evaluated randomly and in consensus by two abdominal radiologists who had no knowledge of the final diagnosis. In two patients with intramural hemorrhage, two separate areas of abnormal small-bowel mural thickening were found. Therefore, 18 abnormal intestinal segments were evaluated in patients with intramural hemorrhage and 19 abnormal segments were evaluated in patients with intestinal ischemia. Images were reviewed on hard copy (n = 22), or if available, images stored on optical disks were retrieved and restored on a workstation (dvantage Windows ; General Electric Medical Systems) (n = 13) running Windows 3.1 (Microsoft; Redmond, W). pattern approach was used to evaluate each abnormal segment. Features used to define an abnormal segment were the degree of mural thickening, location and length of involvement, presence of hemoperitoneum, and pattern of attenuation. The degree of greatest mural thickening was measured (in millimeters) in a segment of thickened bowel that was oriented either longitudinally or axially in the plane of the image. The location of involvement was defined as being predominantly jejunal, ileal, or jejunoileal. The length of involvement was arbitrarily defined as short ( 15 cm), medium (16 30 cm), or long (>30 cm). The pattern of attenuation was defined as being a target appearance (alternating concentric layers of differing attenuation), homogeneous attenuation, or decreased attenuation (lower attenuation than that seen in the adjacent loops of bowel). Consensus interpretation of the scans was performed for several reasons. First, an exact measurement of the length of involvement could not be obtained, given the random orientation of involved loops of small bowel. However, we used the centimeter scale on the side of each CT image to attempt to place each abnormal segment in one of the three categories. We believed that a consensus evaluation was more likely to resolve any ambiguity in the estimation of this parameter. Second, two of the authors in consensus picked the loop of bowel that showed the greatest degree of thickening and that was, at the same time, well distended. Measurement of collapsed segments was avoided. In addition, the loop of bowel needed to be oriented directly perpendicular or parallel to the z-axis so that overestimation of thickness resulting from the oblique orientation could be avoided. ll measurements were calculated by a single author. Wall thickness on the hard copies was measured with a caliper and the centimeter scale on the side of the scan; wall thickness on soft copies was measured with an electronic caliper. We also used consensus interpretation for evaluation of hemoperitoneum. For soft-copy CT scans, a single author placed a round or oval region of interest in the center of the ascites to determine attenuation. ttenuation measuring more than 30 H was considered evidence of hemorrhage. ecause some CT scans were evaluated only on hard copy, a region-of-interest measurement on ascites could not be performed. In these cases, a consensus interpretation was used to determine whether the ascites was highly attenuated relative to other fluid-filled structures, such as renal cysts or the gallbladder. Statistical nalysis To evaluate wall thickening, we used a Mann- Whitney U test to compare segments with ischemia or intramural hemorrhage. Fisher s exact test was used to compare the two patient groups with respect to the location and length of involvement and the presence of hemoperitoneum and a target sign. Results Proof of Diagnosis fter the CT detection of abnormal intestinal thickening and mesenteric findings, we based the final diagnosis on the following factors: Intramural hemorrhage. Of the 16 patients with intramural hemorrhage of the small intestine, proof of diagnosis was based on the clinical evaluation, laboratory findings, and clinical follow-up. ll 16 patients had a predisposing factor for bleeding, including anticoagulation therapy with warfarin sodium tablets (Coumadin; ristol-meyers Squibb, Princeton, NJ) (n = 14) and factor VIII deficiency (n = 2). In the patients recieving anticoagulation therapy, the international normalized ratio level was elevated greater than 4.0 in all 14 patients. In these patients, anticoagulation therapy was discontinued, and no additional 178 JR:180, January 2003

3 CT of Intestinal Ischemia and Hemorrhage therapy was administered. No patient with intramural hemorrhage had an elevated lactic acid level. No patient with intramural hemorrhage underwent surgery. ll patients recovered clinically. Intestinal ischemia. In the 19 patients with ischemia of the small intestine, proof of diagnosis was based either on clinical parameters and follow-up findings or on findings at surgery. Eight patients had intestinal ischemia confirmed at surgery. Three of these eight patients had narrowing or occlusion of the superior mesenteric artery; these patients underwent surgical exploration that confirmed intestinal ischemia (Fig. 1). Five of the eight were found to have nonocclusive low-flow mesenteric ischemia at surgery. In one patient, the diagnosis of smallbowel ischemia was confirmed at autopsy. This patient had a lack of enhancement of a long segment of the distal ileum on CT, and at autopsy, small-bowel infarction was present (Fig. 2). In the remaining 10 patients, the diagnosis was based on imaging and clinical parameters. One patient had thrombosis of the superior mesenteric vein and was treated with anticoagulation therapy (Fig. 3). In the remaining nine patients, the diagnosis of nonocclusive lowflow mesenteric ischemia was based on clini- cal parameters. These nine patients had acute cardiac decompensation or an elevated lactic acid level; they experienced improvement in their symptoms after appropriate resuscitation. None of these patients had an alternative condition such as Crohn s disease or infectious enteritis that was clinically diagnosed. Moreover, none of these patients had an elevated international normalized ratio. Statistical nalysis total of 18 abnormal small-bowel segments were identified in 16 patients with submucosal hemorrhage. Nineteen abnormal Fig. 1. Diffuse small-bowel ischemia in 60-year-old man with occlusive mesenteric ischemia., xial CT scan obtained with IV and oral contrast materials at level of superior mesenteric artery and vein shows diminutive caliber of artery (arrow) relative to vein., xial CT scan obtained at level of inferior mesenteric artery (arrow) shows large caliber of this vessel. Long segment of small-bowel dilatation has minimal wall thickness of 1 2 mm. C, Lateral aortogram shows nonfilling of superior mesenteric artery (SM), celiac axis, and large-caliber inferior mesenteric artery (IM) (arrows). t surgery, patchy areas of necrosis were found in small bowel, requiring small-bowel resection. C JR:180, January

4 Macari et al. segments were present in the 19 patients with intestinal ischemia. Using a pattern approach to CT evaluation of the abnormal small-bowel segments, we found several statistically significant differences between submucosal hemorrhage and intestinal ischemia (Table 1). The mean thickness of segments with intramural hemorrhage was 11.7 mm, and the median was 11 mm (range, 4 25 mm). In segments with small-bowel ischemia, both the mean and the median thicknesses were 4.0 mm (range, 1 9). Mural thickening was found to be statistically more significant (p < 0.001) in the segments with intramural hemorrhage than in those with small-bowel ischemia (Figs. 4 and 5). In the 18 abnormal segments with intramural hemorrhage, six (33%) were located in the jejunum, eight (44%) were in the ileum, three (17%) were in the jejunoileal region, and one (6%) was in the duodenum. Of the 19 ischemic segments, two (11%) were jejunal, seven (37%) were ileal, nine (47%) were jejunoileal, and one (5%) involved the ileocolic region. The two patient groups were not significantly different in terms of location ( p = 0.12). Fourteen (78%) of 18 segments with intramural hemorrhage showed short segment involvement, four (22%) showed mediumlength involvement, and no segment showed long involvement. Of the 10 segments with intestinal ischemia, none showed short segment involvement, three (16%) showed medium-length involvement, and 16 (84%) showed long segment involvement. The abnormal segments with intramural hemorrhage were found to have a significantly shorter length of involvement ( p < ) than did those segments with ischemia (Figs. 6 and 7). Fifteen (94%) of 16 patients with intramural hemorrhage showed hemoperitoneum (Fig. 8). Hemoperitoneum was present in only six (32%) of 19 patients with intestinal ischemia. higher incidence of hemoperitoneum was found in patients with submucosal hemorrhage than in those with ischemia ( p < 0.001). Regarding the pattern of attenuation, the target sign was present in seven (39%) of 18 segments with intramural hemorrhage, and the attenuation was homogeneous in the remaining 11 (61%). The pattern of attenuation in the 19 ischemic segments showed a target appearance in nine (47%) and was homogeneous in nine (47%). One case of small-bowel ischemia showed decreased attenuation in the involved small bowel (5%). The two patient groups were not significantly different in terms of the pattern of attenuation of the mural thickening ( p = 0.18). Discussion The hallmark of an abnormal loop of small bowel on CT is mural thickening. When an abnormal small-bowel segment is detected on CT, the differential diagnosis as to its cause includes neoplasms, inflammatory conditions such as Crohn s disease, vasculitis, radiation enteritis, enteric infections, ischemia, and submucosal hemorrhage [5, 7 9]. Common causes of small-bowel ischemia are poor perfusion resulting from cardiac failure or hypovolemia, arterial embolus or thrombus, and venous thrombosis [3, 10 12]. In recent surgical reviews of mesenteric ischemia, approximately 50% of cases were due to a supefig year-old woman with a long segment of small-bowel infarction. ttenuation of involved small bowel was decreased relative to segments that are not involved., xial CT scan obtained with IV contrast material at level of mid abdomen shows segment of small bowel (thin arrow) with lack of enhancement and thin wall. Other small-bowel loops (thick arrow) show enhancement and mild mural thickening of 2 3 mm. Patient refused surgical intervention., xial CT scan obtained several days later shows intraperitoneal free air (arrow). Patient died several hours later, and autopsy revealed diffuse small-bowel infarction. C Fig. 3. Segmental small-bowel ischemia in 40-year-old woman with thrombosis of superior mesenteric vein., xial CT scan obtained with IV and oral contrast materials at level of superior mesenteric vein shows thrombus (arrow) within vein., xial CT scan obtained several centimeters caudad to shows homogeneous thickening (7 mm) (arrow) in loop of ileum. C, xial CT scan several centimeters caudad to shows continuous homogeneous thickening of ileum (right arrow) to level of terminal ileum (left arrow). pproximately cm of small bowel was estimated to be involved. Patient was treated with anticoagulation therapy and did not require surgery. 180 JR:180, January 2003

5 CT of Intestinal Ischemia and Hemorrhage TLE 1 CT Findings of Small-owel Intramural Hemorrhage and Small-owel Ischemia in 35 Patients CT Feature Intramural Ischemia Hemorrhage (n = 16 patients) a (n = 19 patients) Degree of greatest thickening 18 a (100) 19 (100) Mean (mm) Range (mm) Location of involvement 18 a (100) 19 (100) Jejunum 6 (33) 2 (11) Ileum 8 (44) 7 (37) Jejunoileal region 3 (17) 9 (47) Duodenum 1 (6) 0 Ileocolic region 0 1 (5) Length of involvement 18 a (100) 19 (100) Short ( 15 cm) 14 (78) 0 Medium (16 30 cm) 4 (22) 3 (16) Long (> 30) 0 16 (84) Hemoperitoneum 15/16 (94) 6/19 (32) Pattern of attenuation 18 a (100) 19 (100) Target sign 7 (39) 9 (47) Homogeneous attenuation 11 (61) 9 (47) utopsy finding 0 1 (5) Note Data are number (%) of affected segments. a Two patients had two separate segments affected. rior mesenteric artery embolus, 20 25% were due to a superior mesenteric artery thrombosis, 20 25% were due to nonocclusive mesenteric ischemia, and 5% were due to mesenteric venous thrombosis [10, 11, 13]. The clinical presentation of small-bowel ischemia, irrespective of its cause, includes abdominal pain that is out of proportion to the findings at physical examination, nausea, anorexia, vomiting, and bloody diarrhea [2, 10]. Occult blood may be detected in the stool in nearly 50% of patients. In addition, the clinical presentation varies and depends on the severity of the process; the degree of collateral vascular supply; and, if ischemia is due to vascular occlusion, whether the occluded vessel is an artery or a vein [2, 10, 11]. The nonspecific symptoms and clinical evaluation often result in a delay in the diagnosis. The clinical presentation of patients presenting with spontaneous intramural hemorrhage is also nonspecific and may be similar to that of intestinal ischemia. The findings consist of nausea, vomiting, acute abdominal pain, and gastrointestinal bleeding [14]. The CT findings in bowel ischemia evolve as the process in the bowel wall progresses from ischemia to infarction [3, 7]. Initially, there is mural thickening of the involved bowel segment related to intramural edema [7]. s the process progresses, an element of intramural hemorrhage may be seen [3]. Stranding and hazy changes in the perienteric fat are also usually detected. During the early stages of ischemia, a target sign may be identified in the bowel wall related to the intramural edema and preserved mucosal vasculature [3]. s the bowel becomes more ischemic, a decrease in the attenuation (enhancement) of the affected bowel wall may be present, and the intestinal wall may become thin [3, 4]. However, the early CT findings of intestinal ischemia (mural thickening, perienteric stranding, and a target sign) are not specific and may be present in patients with Crohn s disease; infectious enteritis; radiation changes; and, notably, intramural hemorrhage [3, 7, 14]. CT is helpful in establishing the diagnosis of small-bowel ischemia and has been recommended as the definitive way to diagnose the condition [10]. In patients in whom smallbowel mural thickening is present in addition to mesenteric vascular occlusion or pneumatosis, the CT findings strongly suggest intestinal ischemia. small-caliber aorta and superior mesenteric artery as well as the collapse of the inferior vena cava are helpful secondary findings that suggest hypotensive shock and low-flow nonocclusive ischemia. However, if vascular occlusion is not present or if the CT findings are indeterminate, differentiating ischemia from intramural hemorrhage or inflammatory conditions becomes more difficult. To better characterize an abnormal loop of bowel detected on CT, we analyzed different specific parameters of the abnormal bowel. The pattern approach used in this retrospective evaluation included parameters related Fig. 4. Nonocclusive mesenteric ischemia in 67- year-old man with cardiomyopathy. xial CT scan obtained with IV and oral contrast materials at level of pelvis shows several small-bowel loops with mild (3-mm) mural thickening (arrow). Patient improved with conservative management. to the appearance of the intestinal wall and secondary findings in the mesentery and vascular structures. In CT findings related to the bowel wall, segments with intestinal ischemia showed mild wall thickening, whereas segments with intramural hemorrhage showed more marked thickening a mean of 4.0 mm for intestinal ischemia versus a mean of 11.7 mm for intramural hemorrhage. s stated previously, in irreversible intestinal ischemia, the wall frequently becomes thin, measuring less than JR:180, January

6 Macari et al. Fig. 5. Intramural hemorrhage in 72-yearold man who had elevated international normalized ratio and who was taking anticoagulation medication. xial CT scan obtained with IV and oral contrast materials at level of mid abdomen shows markedly thickened (16-mm) loop of small bowel (arrow). Fig year-old woman with ischemic heart disease and long segment of involvement of nonocclusive mesenteric ischemia., xial CT scan obtained with IV and oral contrast materials at level of pelvis shows multiple small-bowel loops with mild mural thickening of 4 5 mm (arrows)., xial CT scan obtained several centimeters cephalad to shows multiple abnormal small-bowel loops (arrow). pproximately 50 cm of small bowel showed mural thickening. 1 2 mm [3]. The target sign has been well described in the literature in patients with intestinal ischemia but reported infrequently in patients with intramural hemorrhage [3, 6, 7, 14]. In our study, although a target sign was seen more often in patients with ischemia, no significant statistical difference in its presence between the two conditions was found. The detection of the target sign in 39% of patients with intramural hemorrhage in this study is probably due to the use of a power injection of IV contrast material at a relatively fast rate (2 ml/sec) during peak bowel wall enhancement. Scanning during peak enhancement may cause the intramural hemorrhage to continue to appear to be less attenuated than the enhancing mucosa and muscularis. Intramural hemorrhage tends to involve a short segment of small bowel, whereas a greater length of involvement is present in patients with intestinal ischemia. In our CT study, 78% of patients with intramural hemorrhage showed short segmental involvement, but none of the patients with intestinal ischemia showed short segment involvement. Of patients with ischemia, 84% showed long segment involvement. This distribution is probably related to the pathophysiology of intestinal ischemia. In patients with low-flow ischemia, longer segments of small bowel are at risk of hypoxia. Similarly, in patients with superior mesenteric artery obstruction, the embolus usually lodges 3 10 cm from the origin of the vessel, and hence long segments of bowel will be affected [13]. It is un- Fig. 7. Short-segment intramural hemorrhage in 66-year-old man who had elevated international normalized ratio and who was taking anticoagulation medication., xial CT scan obtained with IV and oral contrast materials at level of upper abdomen shows short segment with moderate mural thickening of mm (arrows)., Spot radiograph from small-bowel series shows regular thickened folds in jejunum over short segment of approximately 10 cm (arrows). 182 JR:180, January 2003

7 CT of Intestinal Ischemia and Hemorrhage Fig. 8. Hemoperitoneum in 47-year-old man with intramural hemorrhage. Patient was taking anticoagulation medication and had elevated international normalized ratio. xial CT scan obtained with IV and oral contrast materials at level of jejunum shows abnormal mural thickening with target sign (thick arrow). ssociated hemoperitoneum (thin arrow) is also seen. clear why submucosal hemorrhage tends to involve shorter segments. Previous reports of this condition have described its distribution as being segmental or even mimicking a focal mass [6, 15]. Hemoperitoneum was also shown to be significantly more likely to be present in patients with intramural hemorrhage. Hemoperitoneum was present in 94% of patients with intramural hemorrhage but in only 32% of those with intestinal ischemia. The cause of hemoperitoneum is unclear in patients with intestinal ischemia. It may be related to a secondary intramural hemorrhage and leakage of blood from the serosal surface of the bowel wall. Hemoperitoneum is known to occur in patients with closed-loop smallbowel obstruction and, when present, is considered a specific sign for intestinal ischemia in this setting [16, 17]. In our study, most patients (79%) with intestinal ischemia were likely to have had lowflow nonocclusive disease as a cause. Surgical series have reported a high frequency of superior mesenteric artery embolus as the cause of mesenteric ischemia [11]. lthough the exact reasons for this difference are unclear, it may be related to the age of our patients because the mean age of the patients with intestinal ischemia in our series was 71 years. However, this discrepancy may also be explained by a selection bias in that patients in previously reported surgical series were more likely to have undergone surgery. Nonocclusive mesenteric ischemia, which often manifests as a less severe form of the small-bowel ischemia, may be managed medically, whereas occlusive disease usually requires surgery. The aim of our study was to determine if CT differences exist between small-bowel ischemia and intramural hemorrhage. Therefore, we did not attempt to determine the sensitivity and specificity of CT in the diagnosis of small-bowel ischemia or intramural hemorrhage. In previous studies, the reported range of sensitivity has been 37 80% [3]. This range is likely related to differences in CT technique as well as to the cause and severity of the ischemia. There are several limitations to our study. First, surgical proof was not obtained in most of our patients. Of the 16 patients with small-bowel intramural hemorrhage, all had predisposing factors for bleeding, including anticoagulation therapy in 14 and factor VIII deficiency in two. None of these patients had an elevated lactic acid level, and all improved clinically after the correction of the coagulopathy. In the 19 patients with intestinal ischemia, eight underwent surgery; one patient had intestinal ischemia confirmed at autopsy. One patient had mesenteric vein thrombosis that was treated with anticoagulation therapy. In the remaining nine patients, the diagnosis of low-flow ischemia was based on clinical parameters, including acute cardiac decompensation, an elevated lactic acid level, and an improvement in symptoms after appropriate resuscitation. second limitation involves our finding that the length of involvement is an important differentiating feature between the two conditions. It is difficult to estimate the length of involvement of an abnormal smallbowel segment. lthough we attempted to determine the length of involvement by placing each abnormal small-bowel segment into one of three categories of involvement (short, medium, or long), this system rendered a gross estimate, not an exact measurement. third limitation of our study is that there were a large number of patients with intramural hemorrhage relative to the number of patients with intestinal ischemia, which may reflect a selection bias in the way cases are entered into our CT database. If a patient with abnormal bowel wall thickening also has an initial laboratory value indicating that the international normalized ratio is elevated, that patient s case is likely to be entered into the database as small bowel-hemorrhage. Regarding intestinal ischemia, other conditions may be considered in the initial differential diagnosis. If clinical parameters or specific CT findings such as the narrowing or occlusion of the superior mesenteric artery or vein are not present, cases of ischemia may be entered into the database as smallbowel inflammation, not as small-bowel ischemia. Therefore, more patients with small-bowel ischemia were likely to have undergone CT at our institution than were included in our study. Finally, only contrast-enhanced examinations were included in this study. The diagnosis of submucosal hemorrhage may be facilitated by the use of unenhanced CT scans through recognition of the highly attenuated hemorrhage in the bowel wall [14]. However, if only an unenhanced CT examination is performed, visualization of thrombus or embolus in the superior mesenteric artery or vein cannot be identified. In patients with abdominal pain who are known to be at risk for intramural hemorrhage, an initial unenhanced CT examination may be warranted. Unenhanced CT scans may be helpful for differentiating a hemorrhage from ischemia by showing homogenous high attenuation (>50 H) in the bowel wall, which is indicative of an intramural hemorrhage [2, 5, 6]. However, because most patients with acute abdominal pain undergo CT imaging with oral and IV contrast materials, this finding is often difficult to discern. In conclusion, although some CT findings of intramural hemorrhage and intestinal ischemia overlap (i.e., location of involvement, presence of hemoperitoneum, and the target sign), we found that short segment involvement with a thickness of 1 cm or more is typical of intramural hemorrhage and long segment involvement with thickening of less than 1 cm is typical of ischemia. Evaluation of the superior mesenteric artery and vein is important because occlusion may be seen on contrast-enhanced CT scans. 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