Cauda equina movements during the Valsalva maneuver in patients with lumbar spinal stenosis: introducing a novel method for redundant nerve evaluations.

Objective: To investigate whether inchworm-like cauda equina movements can be observed in patients with lumbar spinal stenosis using a novel Valsalva maneuver cine MRI (cMRI) protocol.

Materials and methods: Fifteen lumbar spinal stenosis patients (11 males; mean age, 73.9 years) underwent lumbar static MRI (sMRI) and sagittal 60-s cMRI. The cMRI protocol, called the Kinematic Assessment of Redundant Nerves (KAoRN), included three resting and Valsalva maneuver sets. Two radiologists independently evaluated cauda equina movement and lumbar spinal stenosis severity from L1/2 to L5/S1 using an MRI lumbar spinal stenosis score. Scores from both analysts were averaged; the most severe averaged score from all levels was extracted and defined as the worst score. Moreover, the level at which severe stenosis (averaged score ≥ 3.5) was observed was counted.

Results: KAoRN-positive cauda equina movement was observed in 11 participants (73.3%). KAoRN-negative participants tended to have non-significantly higher worst lumbar spinal stenosis scores (4.0, interquartile range 3.9-4.0) than those of KAoRN-positive participants (3.5, interquartile range 3.0-4.0) (p = 0.310, χ² test). KAoRN-negative participants tended to have more severe stenosis than that of KAoRN-positive participants, though the difference was not significant (p = 0.182, Wilcoxon rank sum test).

Conclusion: KAoRN-positive cauda equina movement is frequently observed in participants with lumbar spinal stenosis; however, it is not observed in all such cases. Further exploration of the differences in the presence or absence of KAoRN-positive findings may provide new insights into the diagnosis of clinically relevant LSS requiring surgical intervention.

Trail registration: The UMIN clinical trial number: UMIN000052276.