• small bowel obstruction
• free fluid
• CT
• density

Background: Adhesive small bowel obstruction (ASBO) is one of the leading causes of surgical abdominal emergencies and it is associated with high morbidity and mortality rates. The management of ASBO has shifted from immediate surgery to non-operative treatment in the absence of complications. In the acute setting, CT is the preferred imaging technique since it helps to confirm the diagnosis of ASBO, locate the site of obstruction, identify the cause, and detect complications. Patients with ASBO often develop intraabdominal free fluid (IFF), which is widely known as a finding associated with the need for surgical treatment: however, some of the patients with IFF can be discharged with non-operative management. As previous studies suggested, we hypothesized that high-density IFF on CT could be a reliable predictor of surgical treatment.
Methods: Patients diagnosed with ASBO were identified between January 2019 and May 2023. Only patients with IFF > 3 cm2 identified on abdominopelvic CT were included: radiodensity in HU (Hounsfield Units) was measured in the largest pocket of IFF. The HU of patients who underwent surgical treatment was compared with those discharged with non-operative management. Analysis of ROC was performed, and an optimal cut-off value (HU) of IFF was determined using Youden Index. Beyond the radiodensity of IFF, we analysed several other CT findings (e.g., reduced bowel wall enhancement, hyperdense bowel wall on NCCT, transition point) to predict surgical treatment.
Results: A total of 53 patients with ASBO with IFF> 3 cm2 on CT (median age 76 years, 64 % female) were identified. Of these 53 patients, 58% underwent surgical treatment, and 22% required bowel resection. Radiodensity of IFF in the surgical group was significantly higher than that in the non-operative group (median 20 HU vs. 10 HU, p < 0.01). A cut-off value of 15 HU was determined: high-density free fluid (>15) was significantly associated with surgical treatment (p<0.01; OR=91). Sensitivity, specificity, PPV, NPV, and accuracy of high-density IFF (HU>15) to predict the need for surgical treatment were 90.6, 90.4, 93.5, 86.3, and 90.5%, respectively. Reduced bowel wall enhancement was significantly associated with operative management (p < 0.01; OR=42). Hyperdense bowel wall on NCCT had a 100% PPV for bowel resection.
Conclusions: High-density IFF (>15) on CT was significantly associated with the need for surgical treatment in patients with ASBO. Reduced bowel enhancement was significantly more documented in patients who underwent surgery. Hyperdense bowel wall on NCCT was the sole CT sign associated with bowel resection