Multi-detector CT findings in patients with mesenteric ischaemia following cardiopulmonary bypass surgery

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1 Multi-detector CT findings in patients with mesenteric ischaemia following cardiopulmonary bypass surgery Poster No.: C-2340 Congress: ECR 2012 Type: Scientific Exhibit Authors: T. Barrett, S. Upponi, A. Tasker ; Cambridge, Ca/UK, Cambridge/UK Keywords: Ischemia / Infarction, Observer performance, CT, Abdomen DOI: /ecr2012/C-2340 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 11

2 Purpose To retrospectively investigate the CT findings following pathologically-proven mesenteric ischaemia / infarction in patients post-cardiac bypass surgery and compare this to the known features of de novo presenting mesenteric ischaemia. Methods and Materials st st Between 1 January 2000 and 31 December 2009, 68 patients (46 men, 22 women) were identified who met the following inclusion criteria: CT abdomen/pelvis with a report suggesting ischaemic bowel as a differential diagnosis, an operative procedure requiring cardio-pulmonary bypass (CPB) within 1 month of the CT, and laparotomy and/or post mortem within 1 week of the CT. Pathology-proven ischaemic bowel was present in 52 patients; 16 patients had no signs of bowel ischaemia at laparotomy and/or autopsy. The CT examinations were performed on either a 64-slice (n = 45) multi-detector CT or a 4-slice (n = 23) multi-detector CT (Siemens Definition and Siemens Plus 4 Volume Zoom, respectively; Siemens Medical, Forchheim, Germany). Images were acquired in either the arterial phase (n = 3), portal phase (n = 59), or both (n = 6), following mls iopamidol intravenous contrast medium (Niopam 300, Bracco UK Ltd, High Wycombe, UK). The CT images were viewed retrospectively by two readers and assessed for the following parameters: bowel wall thickening, thinning, or oedema, pneumatosis (Figure 1), small bowel faeces sign, mesenteric stranding, bowel obstruction, and dilatation. Vascular parameters assessed were differential mural enhancement (Figure 2), venous thrombus, arterial occlusion, and arterial calcification. Other factors evaluated: presence of ascites, solid organ infarction (Figure 3), free intra-peritoneal air, and mesenteric gas (Figure 4). Additionally the positioning of an intra-aortic balloon pump (IABP) device was evaluated if present. An IABP should be positioned 2-3 cm distal to the left subclavian artery and above the origins of the coeliac axis or superior mesenteric artery; a low position can compromise blood flow within these vessels. Patients with IABPs also receive inotrope support with or without vasoconstrictors, but the use of these agents was not separately recorded. The likelihood of ischaemic bowel being present was also scored on a scale of 1-5 (1 = not present, 2 = unlikely, 3 = possible, 4 = highly likely, 5 = definitely present). Consensus agreement was subsequently agreed upon by three readers in one reporting session. Images for this section: Page 2 of 11

3 Fig. 1: Intramural pneumatosis. A, B: Axial CT images in a 69 year old man following aortic valve replacement surgery show pneumatosis in the stomach wall (arrows). The gas is more clearly seen on bone window pre-sets (B) as opposed to standard abdominal window settings (A). C, D: Coronal (C) and axial (D) CT images in a different patient following coronary artery bypass surgery, with extensive pneumatosis in the small bowel wall (arrows). Fig. 2: Differential bowel wall enhancement in three different patients. A: Differential bowel enhancement with reduced enhancement in the caecum (white arrow) and hyper-enhancement of the small bowel wall (black arrow). B: Differential large bowel Page 3 of 11

4 enhancement with reduced caecal perfusion (white arrows) and normal enhancement of the transverse colon (black arrow). C: Differential small bowel enhancement with areas of reduced enhancement (white arrow) in comparison to areas of more normal enhancement (black arrow). Fig. 3: Solid organ infarction in three different patients following cardio-pulmonary bypass surgery. A: Coronal CT imaging showing peripheral areas of infarction in the liver (arrows). B: Axial CT showing multiple wedge-shaped splenic infarcts (arrows). C: Areas of low attenuation bilateral in the kidneys consistent with infarcts (arrows). Page 4 of 11

5 Fig. 4: Presence of gas within the mesenteric venules. Coronal (A) and axial (B) CT images in a 61 year old man, 2 days following bypass surgery, showing gas locules within small mesenteric vessels (arrows). Page 5 of 11

6 Results The average age of the patient group was 70.6 years (median 73 years; range years). 52 patients were pathologically proven to have ischaemic bowel either following resection at laparotomy (n = 25), autopsy (12), or both (15). 16 patients did not have features of bowel ischaemia at laparotomy and/or autopsy and served as a control group. These patients were shown to have no pathology (6 patients), pseudomembranous colitis (3), a perforated duodenal ulcer, a chest drain perforating the stomach, a retroperitoneal haematoma, diverticulitis, congested large bowel (but no signs of ischaemia), splenic infarcts only, and appendicitis, respectively. The most frequent operation requiring cardio-pulmonary bypass (CPB) was coronary artery bypass grafting (CABG; n = 38), followed by CABG with aortic valve replacement (11); Table 1. The average time from initial CPB operation to CT was 6.82 days (median 5 days; range 1-25 days). For patients undergoing laparotomy, the average time was 1.16 days (range 0-7 days). The majority of patients had laparotomy within 48 hours of the CT (42/50); 26 of these were within 24 hours. Overall inter-reader agreement was good-to excellent for most signs (Kappa-coefficient > 0.5). The Kappa agreement was poor for bowel wall thinning (# = -0.01), venous thrombus (-0.02), mesenteric stranding (0.45), and differential mural enhancement (0.49); Table 2. The most common findings in those with proven ischaemic bowel were differential wall enhancement, seen in 48/52 patients (92.3%), ascites in 45/52 (86.5%) and mesenteric stranding in 34/52 (65.4%). Neither bowel obstruction nor venous thrombus was demonstrated in any of the patients (Table 2). The highest specificity and positive predictive value (PPV) results were for seen with pneumatosis (specificity 0.81; PPV 0.91), mural thinning (0.88; 0.91), small bowel faeces sign (0.94; 0.93), and arterial occlusion (0.88; 0.86); Table 3. In those with proven ischaemic bowel, the fewest number of CT signs present was 3, the most 13 (average 7.5, median 7), for those with no ischaemia pathologically the range was 0-13 signs (average 5.2, median 6). Scores for overall consensus likelihood of ischaemic bowel being present were higher for cases of ischaemic bowel, with 80.8% scoring 4 (highly likely) or 5 (definitely present) and only 1 patient scoring 1 (not present) or 2 (unlikely). However, although the overall scores for non-ischaemic bowel were lower, 31.25% of cases stilled scored '4' and 18.75% scored '5' for probability of ischaemic bowel; Table 4. Images for this section: Page 6 of 11

7 Table 1: Operation performed and frequency. CABG = coronary artery bypass graft, AVR = aortic valve replacement, MV = mitral valve, TR = tricuspid valve. Page 7 of 11

8 Table 2: Consensus frequency of the respective CT signs in patients with and without ischaemic bowel and correlation statistics for inter-reader agreement on CT signs of ischaemic bowel. Page 8 of 11

9 Table 3: Sensitivity, specificity, positive and negative predictive values per sign, including confidence intervals (CI). Table 4: Consensus reader confidence of ischaemic bowel likelihood. IB = ischaemic bowel (inter-reader correlation = 0.71). Page 9 of 11

10 Conclusion There was overlap amongst the groups for consensus scores for the probability of ischaemic bowel presence based on CT and the overall number of signs present. The signs that were better for predicting the presence of ischaemic bowel based on specificity and PPV were pneumatosis, mural thinning, small bowel faeces sign, and arterial occlusion. Overall, the negative predictive value and sensitivity of each of the signs was low, which is partly explained by the relatively small number of control cases and also by the overlap of signs amongst the groups. These findings are, however, consistent with those of previous authors [1]. The choice of a control group in which the diagnosis of ischaemic bowel was clinically possible serves to better parallel daily practice, undoubtedly the respective specificities would be higher if a healthy patient control group was selected. The prevalence of arterial occlusion (23.1%) and venous thrombosis (0%) was relatively low in our study, compared to other studies where arterial occlusion was seen in >50% cases [2, 3] and venous thrombosis in 15-21% for venous thrombosis [1, 3]. This is expected in a population of patients following CPD surgery, where poor cardiac output and hypo-perfusion leads to non-occlusive ischaemia [4]. The incidence of solid organ (61.5%) is also relatively high which may be due to peri-operative factors and subsequent micro-emboli. Based on the Kappa-correlation statistics for inter-reader agreement it would appear that the following signs are the hardest to interpret: bowel wall thinning, mesenteric stranding (possibly due to the frequent concurrent presence of ascites), and differential mural enhancement. The poor result for venous thrombosis is likely explained by its low prevalence in the patient group: the two readers each identified the sign once in separate patients, but on consensus this was deemed to be due to artefact. Knowledge of difficult to appreciate signs where inter-observer agreement was poor is useful to enable interpretation. The selected patient group brings additional problems in terms of symptomatology, with the majority being unable to offer a history of abdominal pain given the time post-operatively. Other indicators can be predictive of ischaemic bowel such as perioperative factors, the development of post-operative renal failure, a raised blood lactate level, and signs elicited on examination [5]. There is a degree of overlap between the individual signs present at CT and the overall number of signs present in patients with suspected ischaemic bowel following an operation incorporating cardio-pulmonary bypass. It may be that patients with obvious clinic features of ischaemic bowel were operated on immediately without CT. This could possibly explain the lack of sensitivity of CT in achieving diagnosis in the remaining cases. Nevertheless, in line with previous authors [4], our findings suggest a low threshold for undertaking laparotomy should be adopted if clinical suspicion is high. Page 10 of 11

11 References [1] Taourel PG, Deneuville M, Pradel JA, Régent D, Bruel JM. Radiology. Acute mesenteric ischemia: diagnosis with contrast-enhanced CT. 1996; 199(3):632-6 [2] Chou CK, Mak CW, Tzeng WS, Chang JM. CT of small bowel ischemia. Abdom Imaging. 2004; 29(1):18-22 [3] Aschoff AJ, Stuber G, Becker BW, Hoffmann MH, Schmitz BL, Schelzig H, Jaeckle T. Evaluation of acute mesenteric ischemia: accuracy of biphasic mesenteric multidetector CT angiography. Abdom Imaging. 2009; 34(3): [4] Abboud B, Daher R, Boujaoude J.World J Gastroenterol. Acute mesenteric ischemia after cardio-pulmonary bypass surgery Sep 21;14(35): [5] Venkateswaran RV, Charman SC, Goddard M, Large SR. Lethal mesenteric ischaemia after cardiopulmonary bypass: a common complication? Eur J Cardiothorac Surg. 2002; 22(4):534-8 Personal Information Page 11 of 11