Can a computed tomography (CT) scan of the abdomen without intravenous (IV) contrast demonstrate intestinal obstruction?

From the Guidelines

A CT scan of the abdomen without IV contrast can indeed show obstruction, with a diagnostic accuracy of more than 90% reported in the literature. This type of scan can effectively identify dilated bowel loops, transition points, and fecal loading patterns that are characteristic of intestinal obstruction, as noted in the study by 1. Without contrast, the scan can still demonstrate differences in tissue density that help radiologists identify obstructed areas, particularly when there is a significant difference between fluid-filled dilated bowel segments and collapsed bowel. Some key points to consider when using a non-contrast CT scan to diagnose obstruction include:

• The use of multidetector CT scanners with multiplanar reconstruction capabilities, which have been shown to be more effective for evaluating SBO and other abdominal pathology 1
• The ability to identify the transition zone in SBO, which can be a useful adjunct if an operative intervention is planned 1
• The potential limitations of non-contrast CT in determining ischemia, which may be reduced compared to CT with IV contrast 1 However, it's essential to note that while non-contrast CT scans can detect most mechanical obstructions, IV contrast would provide additional information about bowel wall enhancement, vascular complications, or underlying causes such as tumors or inflammatory conditions, as discussed in the study by 1. For this reason, the radiologist might recommend a follow-up contrast-enhanced study if the initial non-contrast scan is inconclusive or if more detailed information about the cause of obstruction is needed.

From the Research

CT Scan of Abdomen without IV Contrast

• A CT scan of the abdomen without IV contrast can show obstruction, as studies have demonstrated that unenhanced CT scans can identify the etiology of bowel obstruction with sensitivity similar to that of contrast-enhanced CT scans 2.
• The sensitivity of unenhanced CT scans in diagnosing small bowel obstruction was 64%, while that of enhanced CT scans was 73%, with no significant difference between the two 2.
• In the case of large bowel obstruction, the sensitivity of unenhanced CT scans was 71%, while that of enhanced CT scans was 100% 2.
• Adhesions were identified as the etiology of small bowel obstruction on unenhanced CT scans in 80% of patients, while tumors were identified as the etiology of large bowel obstruction on unenhanced CT scans in 67% of patients 2.

Diagnostic Accuracy of CT Scans

• CT scans have been shown to be highly accurate in diagnosing bowel obstruction, with an overall sensitivity of 94%, specificity of 96%, and accuracy of 95% 3.
• The cause of obstruction was correctly predicted in 73% of cases using CT scans 3.
• CT scans are most useful in patients with a history of abdominal malignancy and in patients who have not been operated on and who have signs of infection, bowel infarction, or a palpable abdominal mass 3.

Role of CT Scans in Management

• CT scans can play a role in the management of bowel obstruction, particularly in identifying patients who require immediate surgery 4.
• However, CT scans may not be necessary in all cases, and other imaging modalities such as plain radiographs and contrast imaging/fluoroscopy may be sufficient 4, 5.