Changes in dural sac caliber with standing MRI improve correlation with symptoms of lumbar spinal stenosis

Yvonne Yan On Lau, Ryan Ka Lok Lee, James Francis Griffith, Carol Lai Yee Chan, Sheung Wai Law, Kin On Kwok

Weight bearing does alter the dimension of lumbar spinal canal, but no study has analyzed its clinical correlation. This study aims to evaluate whether the changes in dural sac cross-sectional area (DSCA) and sagittal anteroposterior (AP) diameter on standing magnetic resonance imaging (MRI) correlate better with clinical symptoms of lumbar spinal stenosis. Seventy consecutive patients with neurogenic claudication were prospectively recruited to undergo a 0.25-T MRI examination performed in supine and standing positions. Clinical symptoms including the walking distance, Visual Analogue Score of leg pain, Chinese Oswestry Disability Index, and short form-12 were assessed. DSCA and sagittal AP diameter at the most constricted spinal level on supine and standing positions were measured and correlated with each clinical symptom by Pearson correlation coefficients (r). DSCA and AP diameter on standing MRI and their % changes from supine to standing showed significant (r = 0.55, 0.53, -0.44, -0.43; p < 0.001) and better correlations than those on supine MRI (r = 0.39, 0.42; p < 0.001) with walking distance. Significant correlations were also found between dural sac calibers on standing MRI and leg pain scores (r = -0.20, r = -0.25; p < 0.05). Patients walking ≤500 m had a significantly smaller DSCA, narrower AP diameter and greater % change in dural sac calibers (p < 0.01) than those walking >500 m. A >30% reduction of DSCA and AP diameter was observed in patients with worse claudication distance (p < 0.05). DSCA and sagittal AP diameter on standing MRI correlate significantly and better than findings on supine MRI with claudication symptoms. Standing MRI demonstrates dynamic changes of dural sac and provides an additional value to supine MRI in correlating clinical symptoms of lumbar spinal stenosis.