MRI criteria of developmental lumbar spinal stenosis revisited.

Purpose: It is somewhat surprising that radiographic criteria for lumbar stenosis have been transposed from radiography and CT to MR without scientific validation. As these radiographic criteria were developed via population studies with criteria defined by two standard deviations from the mean, we sought to perform the same methodology via MR.

Methods: The study was approved by the institutional review board; the requirement for informed consent was waived. One-hundred patients referred for possible metastatic disease, aged 4 to 94 were studied. Measurements were obtained on a midline sagittal T2-weighted (6000/120) image at each disc level, as well as at the mid-vertebral level. The distributive mean, and standard deviations were calculated and -2 SD was used as a "cutoff" for spinal stenosis. To assess for interobserver variation, 20% of the measurements were repeated by a second observer. To assess for intraobserver variation, another 20% of the measurements were repeated a second time at a minimum of a two month interval.

Results: The spinal canal was narrowest at L5-S1 (mean: 1.16 cm), and widest at L1-L2 (mean: 1.56 cm). Overall the narrowest measurements were at the intervertebral disc space and were narrower at the lower disc spaces. In our population, the lowest cutoff limit (two standard deviations below the mean) had a range between 0.38 cm at the L3-L4 disc space and 0.9 cm at the L1 vertebral level. Notably at the L3 level the size range was from 0.77 to 1.75

Conclusion: Traditional measurements of canal diameters may be too large when applied to soft tissue analysis on MR. We suggest using a cutoff of smaller than 0.90 cm for developmental stenosis.