Multidetector CT findings in patients with mesenteric ischaemia following cardiopulmonary bypass surgery

Abstract

Objective: To investigate CT findings in patients with pathologically proven mesenteric ischaemia post-cardiopulmonary bypass surgery and compare them with the control group of patients without ischaemia.

Methods: 68 patients were identified by a search of local surgical and pathological databases; these patients met the inclusion criteria of a laparotomy within 1 month of a procedure requiring cardiopulmonary bypass and a CT abdomen/pelvis within 1 week of the pathological diagnosis. Two radiologists independently reviewed the studies, evaluating 17 separate findings relating to the bowel, the vasculature or other structures; consensus was subsequently reached. The diagnostic value of CT findings was assessed using logistic regression.

Results: 52 of 68 patients had pathologically proven ischaemia. Portal venous gas, mesenteric venous gas and small bowel faeces sign all had specificities of >0.94 for ischaemia but low sensitivity (<0.27). Differential mural enhancement had high sensitivity (0.92) but poor specificity (0.50). The combination of pneumatosis, bowel loop dilatation and differential mural enhancement predicted bowel ischaemia with a probability of 98%. The hardest signs to interpret based on poor interreader kappa agreement were bowel wall thinning, mesenteric stranding and differential mural enhancement.

Conclusion: A combination of CT signs was predictive of ischaemic bowel; however, the more specific findings lacked sensitivity. If clinical suspicion is high for bowel ischaemia, prompt surgical intervention is warranted, regardless of CT findings.

Advances in knowledge: Arterial occlusion was uncommon and venous occlusion was not present, which is supportive of a predominantly non-occlusive aetiology for ischaemia in this patient group.

Figure 1.

Patients’ selection flow chart. CPB, cardio-pulmonary bypass.

Figure 2.

Extensive intramural pneumatosis. CT imaging in a 69-year-old male, 3 days post redo aortic valve replacement bioprosthesis surgery. Coronal reformats (a,b) and axial slices (c,d) show extensive pneumatosis in the bowel wall (arrows). The gas is more clearly demonstrated using bone window presets (b,d) than with the equivalent slices on standard abdominal window settings (a,c).

Figure 3.

Small bowel faeces sign. Axial (a) and coronal (b) reformatted CT images in an 80-year-old male patient, 3 days following coronary artery bypass graft surgery, show small bowel faeces sign (white arrows), a more proximal loop of jejunum is seen to be fluid-filled (black arrow).

Figure 4.

Differential bowel wall enhancement. (a) A 79-year-old female patient, 1 day post coronary artery bypass graft. Adjacent loops of ileum show differential enhancement with hypo- (white arrows) and hyperenhancement (black arrow). (b) Axial CT in a different patient showing differential enhancement of the descending colon with hyperenhancement of the medial wall (black arrow) and reduced enhancement and oedema of the lateral wall (white arrow).

Figure 5.

Portal venous gas. (a,b) Axial CT images from a 79-year-old male, 4 days following coronary artery bypass graft (CABG) with aortic valve replacement (AVR), show locules of gas within peripheral portal vein branches (black arrows). (c) Axial CT slice from a 61-year-old male patient, 3 days post combined CABG/AVR surgery, shows gas in the extrahepatic portion of the main portal vein (white arrow); the gas lies anteriorly with the patient positioned supine.

Figure 6.

Solid organ hypoperfusion/infarction. (a,b) Axial CT imaging (a) with coronal reformats (b) in a 41-year-old female patient, 4 days post coronary artery bypass graft surgery, shows peripheral wedge-shaped areas of hypoperfusion in the liver (arrows). (c) Axial CT in an 82-year-old female patient, 10 days post aortic valve replacement (AVR) with multiple splenic infarcts (arrows). (d) A 65-year-old male patient, 14 days post mitral and AVR surgery with bilateral renal infarcts (arrows).

Figure 7.

Gas within mesenteric vessel. Portal phase imaging in a 61-year-old male patient, 2 days post coronary artery bypass graft surgery. Multiplanar coronal reformats (a,c) and axial CT (b) show multiple locules of gas within small peripheral mesenteric veins (arrows).

Figure 8.

(a) Receiver operating characteristic (ROC) curve using the number of signs present (maximum observed=13). (b) Sensitivity and specificity by number of signs present. CI, contidence interval.