Is contrast necessary on a Computed Tomography (CT) scan to visualize discs?

From the Guidelines

No, contrast is not necessary on a CT scan to visualize intervertebral discs. Standard non-contrast CT scans can adequately display disc morphology, including herniation, bulging, and degenerative changes, as stated in the study by 1. The discs appear as hypodense (darker) structures between the vertebral bodies on CT imaging due to their fibrocartilaginous composition, which has different density than the surrounding bone.

Some key points to consider:

• CT lumbar spine without IV contrast can be helpful in assessing osseous fusion and detecting potentially painful hardware failure, including prosthetic loosening, malalignment, or metallic fracture, as mentioned in the study by 1.
• The addition of IV contrast is not necessary to evaluate bony fusion and hardware but may be useful to assess for epidural abscess in patients with specific clinical scenarios, as noted in the study by 1.
• CT myelography of the lumbar spine can be useful in assessing the patency of the spinal canal/thecal sac and of the subarticular recesses and neural foramen, but it has the disadvantage of requiring lumbar puncture for intrathecal injection of myelographic contrast, as stated in the study by 1.
• MRI remains the gold standard for detailed disc evaluation because it provides superior soft tissue contrast and can better demonstrate disc hydration status, internal structure, and nerve root compression without radiation exposure, as mentioned in the study by 1.

However, contrast may occasionally be used in specific situations, such as when there's suspicion of infection, inflammation, or tumors affecting the discs or surrounding tissues, as noted in the study by 1. In these cases, the contrast helps highlight areas of abnormal vascularity or disruption of the blood-disc barrier.

It's also worth noting that CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, and a recent retrospective review showed that 50% thecal sac effacement on CT predicted significant spinal stenosis, and <50% thecal sac effacement reliably excluded cauda equina impingement, using MRI as the reference standard, as mentioned in the study by 1.

From the FDA Drug Label

Following intrathecal injection in conventional radiography, OMNIPAQUE 300 will continue to provide good diagnostic contrast for at least 30 minutes At approximately 1 hour following injection, contrast of diagnostic quality will no longer be available for conventional myelography If computerized tomographic (CT) myelography is to follow, consideration should be given to a delay of several hours to allow the degree of contrast to decrease

The use of contrast is necessary to visualize discs on a CT scan, as it provides diagnostic contrast. However, the timing of the CT scan after contrast administration is crucial, and a delay of several hours may be necessary to allow the degree of contrast to decrease 2.

From the Research

Visualization of Discs on CT Scans

To visualize discs on a Computed Tomography (CT) scan, the necessity of contrast depends on various factors, including the specific condition being diagnosed and the capabilities of the CT technology used.

• The use of contrast in CT scans can enhance the visibility of certain anatomical structures and pathologies, including spinal stenosis and disc degeneration 3, 4.
• However, studies have shown that magnetic resonance imaging (MRI) is more sensitive than contrast CT in demonstrating disc degeneration, with one study finding that MRI showed disc degeneration in 74 of 123 segments, while CT showed disc degeneration disease in 27 of 123 segments 3.
• In the diagnosis of lumbar disc herniation, surface coil MRI has been found to be superior to contrast CT, with a higher sensitivity and specificity 4.
• There is evidence to suggest that high-resolution CT scans can diagnose herniated lumbar discs without the use of intrathecal contrast, with one study achieving a diagnosis in 83% of cases that had a positive myelogram 5.
• The administration of iodinated contrast agents in CT scans is a complex process, influenced by various factors such as patient weight, cardiac output, and technical characteristics of the scan, and requires optimization to achieve the best results 6.
• The use of intravenous iodinated contrast media in patients with kidney disease has been a topic of discussion, with consensus statements from the American College of Radiology and the National Kidney Foundation providing guidance on the safe use of these agents in patients with reduced kidney function 7.