Dynamic changes in the dural sac of patients with lumbar canal stenosis evaluated by multidetector-row computed tomography after myelography

Some reported studies have evaluated the dural sac in patients with lumbar spinal stenosis (LSS) by computed tomography (CT) after conventional myelography or magnetic resonance imaging (MRI). But they have been only able to evaluate static factors. No reports have described detailed dynamic changes in the dural sac during flexion and extension observed by multidetector-row computed tomography (MDCT). The aim of this study was to elucidate or demonstrate, in detail, the influence of dynamic factors on the severity of stenosis. One hundred patients with LSS were enrolled in this study. All underwent MDCT in both flexion and extension positions after myelography, in addition to undergoing MRI. The anteroposterior diameter (AP-distance) and cross-sectional area of the dural sac (D-area) were measured at each disc level between L1-2 and L5-S1. The dynamic change in the D-area was defined as the absolute value of the difference between flexion and extension. The rate of dynamic change (dynamic change in D-area/D-area at flexion) in the dural sac at each disc level was also calculated. The average AP-distance in flexion/extension (mm) was 9.2/7.4 at L3-4 and 8.3/7.4 at L4-5. The average D-area in flexion/extension (mm(2)) was 96.3/73.6 at L3-4 and 72.3/61.0 at L4-5. The values were significantly lower in extension than in flexion at all disc levels from L1-2 to L5-S1. AP-distance was narrowest and D-area smallest at L4-5 during extension. The rates of dynamic changes at L2-3 and L3-4 were higher than those at L4-5. MDCT clearly elucidated the dynamic changes in the lumbar dural sac. Before surgery, MDCT after myelography should be used to evaluate the dynamic change during flexion and extension, especially at L2-3, L3-4, and L4-5.