In vivo MRI diffusion changes first precursor to indicate disc degeneration

First in vivo study on diffusion pattern finds diffusion changes may signal disc degeneration.

Issue: Issue 3 2006

Using MRIs to detect changes in lumbar disc diffusion patterns helps identify endplate damage in vivo and its physiological effects on disc diffusion, according to an Indian surgeon and his colleagues.

S. Rajasekaran, PhD, of Ganga Hospital in Coimbatore, India, and colleagues recorded the 24-hour temporal diffusion patterns in human lumbar discs.

The researchers found that diffusion changes may be the first precursor to disc degeneration.

Additionally, the changes can help differentiate between disc degeneration and prolapse, said Rajasekaran, who presented the study results at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting.

“Not only [does it] cause diffusion, but a break to the endplate can cause an inflammatory response, can instigate an autoimmune response, can decrease nutrition and increase cell death, and cause a drop in nucleus pulposus pressure,” he said.

In vivo MRI study

Rajasekaran and colleagues included 215 discs of 43 patients for the in vivo study. This included 10 volunteer patients with no history of back pain and 33 patients being investigated for back pain. Of the 215 discs, the researchers studied 150 discs (96 normal discs and 54 degenerating discs).

All patients received injections of gadodiamide dye at 0.3 µmol/kg body weight, Rajasekaran said. The researchers then used a 0.5 Tesla MR imager to perform a series of MRIs over 24 hours following injection.

The researchers calculated diffusion by measuring signal intensity in the vertebral body, subchondral bone, endplate, center nucleus pulposus and the peripheral nucleus pulposus.

They further evaluated the diffusion characteristics in each region, measuring the enhancement percentage for each MRI taken throughout the 24-hour period as well as the peak enhancement percentage and the time to achieve peak enhancement percentage, Rajasekaran said.

Normal pattern findings

Two observers evaluated the MRIs, with an interobserver agreement of 82.6%, a Kappa value of 0.868 and a confidence interval of 0.768 to 0.912, according to the study.

In precontrast images, an intact endplate appeared as a distinct zone that was hypointense to the subchondral bone and nucleus pulposus by 75 units, the observers found.

In postcontrast images, a normal diffusion pattern appeared as a sequential achievement in the peak enhancement percentage from the vertebral body to the central nucleus pulposus, with a delay at the endplate. Rajasekaran referred to this sequence as the diffusion march.

“The vertebral body reaches its maximum within 10 minutes, and so does the subchondral bone,” Rajasekaran said. “But when you look at the endplate, it takes two hours for it to reach the maximum peak. And [for] the peripheral nucleus pulposus … time to peak there is six hours, and the central nucleus pulposus is about the same.”

Endplate break findings

The observers identified endplate breaks by absence of endplate delay and diffusion march, as well as a focal absence of hypointensity.

Endplate break zones appeared as patchy areas and “the vertebral body, the subchondral bone and peripheral nucleus pulposus … made enhancements within 10 minutes, which is significant and different from the normal [pattern],” Rajasekaran said.

Similar to the vertebral body and subchondral bone, the peripheral nucleus pulposus and endplate lost enhancement by the two-hour mark, but the central nucleus pulposus continued enhancement, Rajasekaran said.

The researchers also found that the incidence of tidal breaks increased with age (P<.001), with significant increases between the third and fourth decades as well as the fourth and fifth decades (P<.001).

Rajasekaran noted that such imaging studies could be applied to other spinal conditions, such as scoliosis. But he cautioned that the endplates must be intact in order to apply certain treatments, such as gene or stem cell therapies.

For more information:

Rajasekaran S, Babu J, Shetty A, et al. In-vivo identification of endplate damage in human lumbar discs by post-contrast MRI studies. #110. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26. Chicago.