What is the difference between a computed tomography (CT) scan of the abdomen with contrast administered first versus without contrast, in detecting postoperative complications?

From the Guidelines

For postoperative complication evaluation, a CT abdomen with contrast is generally better than a CT abdomen with contrast first, as it provides optimal visualization of most abdominal organs and potential complications during the portal venous phase. The main difference between these two studies is the timing of image acquisition relative to contrast administration. A CT with contrast involves injecting intravenous contrast material and then obtaining images during the portal venous phase (typically 60-70 seconds after injection), which provides excellent visualization of most pathologies while minimizing radiation exposure 1.

Key Considerations

• The portal venous phase is typically sufficient for evaluating most postoperative complications, such as abscess, anastomotic leak, hematoma, or bowel obstruction.
• The multiphasic approach with contrast first is primarily beneficial when evaluating vascular complications (like arterial bleeding or thrombosis), hypervascular tumors, or specific organ perfusion issues 1.
• If there is clinical suspicion for active bleeding or vascular complications after surgery, then the multiphasic approach with contrast first would be more appropriate.
• The standard dose for intravenous contrast is typically 100-150 mL of iodinated contrast material administered at 3-5 mL/second, with specific timing protocols programmed into the CT scanner to capture the appropriate phases.

Evidence-Based Recommendations

• According to the American College of Radiology, CT of the abdomen and pelvis with IV contrast is usually appropriate to evaluate for postoperative abscesses, leaks, or hemorrhage 1.
• A study published in the Journal of the American College of Radiology found that CT with IV contrast is important for the evaluation of the integrity of the bowel wall when ischemia or anastomotic dehiscence is suspected 1.
• Another study suggested that arterial phase imaging can be used to complement portal-venous imaging for the detection of RCC metastases to the liver, pancreas, and contralateral kidney 1.

Clinical Implications

• The choice of CT protocol should be based on the specific clinical scenario and the suspected complication.
• Clinicians should consider the benefits and limitations of each protocol, including radiation exposure and the potential for detecting specific complications.
• The use of IV contrast is generally recommended, unless contraindicated, to provide optimal visualization of abdominal organs and potential complications 1.

From the Research

CT Abdomen with Contrast

• A CT abdomen with contrast is used to diagnose postoperative complications, as it provides better visualization of the abdominal structures and any potential complications 2, 3, 4.
• The use of contrast media with different iodine concentrations does not significantly affect the image quality of enhanced computed tomography, as long as the iodine delivery rate and iodine load are similar 5, 6.

Contrast-First vs Contrast

• There is no significant difference in image quality between using contrast media with different iodine concentrations, such as 400 mg I/mL and 300 mg I/mL, when the iodine delivery rate and iodine load are similar 6.
• A size-based contrast reduction algorithm using low kV and bolus tracking can reduce iodine contrast dose by 50% while achieving acceptable image quality in 95% of exams 5.

Postoperative Complication Diagnosis

• CT scan is the gold standard for follow-up after abdominal surgery and diagnosis of postoperative complications, including small bowel obstruction, peritonitis, and wall complications 2, 3, 4.
• The diagnosis of postoperative peritonitis is difficult on imaging, but fluid collections are frequent and easily detected 2.
• Other postoperative complications, such as hematoma, infections, and wound hernia, can be diagnosed using CT scans 2, 3.