Clinical and radiographic characteristics of the patients

Table 1 presents the patients’ clinical and radiographic characteristics. A peritoneal irritation sign was observed in 19 patients (36.5%), and 22 patients (42.4%) had preoperative systemic inflammatory response syndrome (SIRS). The causes of SBO were adhesions (n = 31, 59.6%), internal hernias (n = 14, 26.9%), intestinal volvulus (n = 5, 9.6%), and intussusceptions (n = 2, 3.9%). CT findings revealed ascites in 51 patients (98.1%), closed loops in 27 patients (51.9%), and the whirl sign in 10 patients (19.2%). The mean CT values of poorly enhanced intestinal walls and liver parenchyma were 41.74 ± 9.31 and 96.60 ± 4.39 HU, respectively. The mean CT values of the liver parenchyma followed a normal distribution. The median intestinal-to-liver CT attenuation ratio was 0.40 (range, 0.29–0.72). Regarding postoperative outcomes, 13 patients (25%) experienced complications, and the mean postoperative hospitalization duration was 11.96 ± 6.91 days. One patient (1.9%) in the resection group died of multiple organ failure.

Table 1 Clinical and radiographic characteristics of 52 patients enrolled in this studyComparison of clinical and radiographic factors between the two groups

Table 2 presents the associations between the clinical and radiographic factors. No significant differences in age, sex, peritoneal irritation sign, preoperative SIRS, causes of SBO, CRP, K, CK, LDH, blood gas analysis (pH, PaO2, PaCO2, HCO3-, and lactic acid), or CT findings (ascites, closed loop, whirl sign, and mesenteric edema) were observed between the two groups. However, the resection group had a significantly longer time from onset to surgery (p = 0.034) and a higher WBC count (p = 0.037) than the no resection group. Furthermore, the CT values of poorly enhanced intestinal walls (p < 0.0001) and intestinal-to-liver CT attenuation ratio (p < 0.0001) were significantly lower in the resection group than in the no resection group. Regarding postoperative outcomes, no significant differences in the incidence of postoperative complications, postoperative hospitalization, or overall clinical outcomes were observed between the two groups.

Table 2 Comparison of clinical and radiographic characteristics between intestinal resection group and no resection groupUnivariate and multivariate analyses of intestinal resection

Univariate analysis revealed that time from onset to surgery (OR, 3.60; CI, 1.038–12.481; p = 0.0435), WBC count (OR, 3.57; CI, 1.062–12.010; p = 0.0397), and intestinal-to-liver CT attenuation ratio (OR, 14.375; CI, 2.810–73.527; p = 0.0014) were significantly associated with the need for intestinal resection, using the median of time from onset to surgery, the normal upper limit WBC as defined by the Japan Committee for Clinical Laboratory Standards, and the median of CT attenuation ratio as cutoff values. In the multivariate analysis using nominal logistic regression, the time from onset to surgery (OR, 5.08; CI, 1.106–23.350; p = 0.037) and intestinal-to-liver CT attenuation ratio (OR, 15.50; CI, 2.622–91.686; p = 0.0025) were identified as independent predictive factors (Table 3).

Table 3 Predictive factors for intestinal ischemia requiring for SBO by univariate and multivariate analysisIntestinal resection rate, accuracy, sensitivity, and specificity of the intestinal-to-liver CT Attenuation value ratio (< 0.40) based on time from onset to surgery

The AUROC of the intestine-to-liver CT attenuation ratio for predicting need for resection was 0.886 (Youden index; 0.736, 95%CI; 0.767–0.957), with an optimal cutoff around 0.47 yielding sensitivity 97.1% and specificity 76.5% (Fig. 2). The intestinal resection rate for intestinal ischemia was evaluated by classifying the median of the intestinal-to-liver CT attenuation ratio as a cutoff value because it was clinically applicable and easy to interpret, and the number of cases is uniformly (Table 4). The resection rate of the CT attenuation ratio (< 0.40) was 92%, and the resection rate of the CT attenuation ratio (≥ 0.40) was 44.4% (p = 0.0001). The accuracy, sensitivity, and specificity of the intestinal-to-liver CT attenuation ratio (< 0.40) for predicting the need for intestinal resection within 12 h from onset to surgery were 76.5%, 66.7%, and 87.5%, respectively (Table 5). Furthermore, the PPV and NPV were 85.7% and 70%, respectively. In contrast, for cases in which surgery was performed > 24 h after onset, the accuracy, sensitivity, and specificity were 66.7%, 58.3%, and 100%. The AUROC within 12 h from onset to surgery was 0.903, that from 12 h to 24 h after onset was 0.869, and that from > 24 h after onset was 0.972 (Table 6; Fig. 2).

Table 4 Comparison of the resection rate between CT Attenuation ratio ≥ 0.40 and < 0.40Table 5 Accuracy, sensitivity, specificity, PPV, and NPV according to the time from onset to surgery for CT values ratio (< 0.40)Table 6 The area under the ROC curves (AUROC) by categorizing the time from onset to surgeryFig. 2

Each ROC curve for categorizing the time from onset to surgery. a: ROC curve of the intestine-to-liver CT attenuation ratio for predicting need for resection. AUC was 0.886. b: ROC curve within 12 h from onset to surgery. AUC was 0.903. c: ROC curve from 12 h to 24 h after onset. AUC was 0.869. d: ROC curve from > 24 h after onset. AUC was 0.972