Introduction: Quantitative measures of degree of lumbar spinal
stenosis (LSS) such as antero-posterior diameter of the canal or dural
sac cross sectional area vary widely and do not correlate with clinical
symptoms or results of surgical decompression. In an effort to improve
quantification of stenosis we have developed a grading system based
on the morphology of the dural sac and its contents as seen on T2
axial images. The grading comprises seven categories ranging form
normal to the most severe stenosis and takes into account the ratio of
rootlet/CSF content.
Material and methods: Fifty T2 axial MRI images taken at disc level
from twenty seven symptomatic lumbar spinal stenosis patients
who underwent decompressive surgery were classified into seven
categories by five observers and reclassified 2 weeks later by
the same investigators. Intra- and inter-observer reliability of the
classification were assessed using Cohen's and Fleiss' kappa
statistics, respectively.
Results: Generally, the morphology grading system itself was well
adopted by the observers. Its success in application is strongly
influenced by the identification of the dural sac. The average intraobserver
Cohen's kappa was 0.53 ± 0.2. The inter-observer Fleiss'
kappa was 0.38 ± 0.02 in the first rating and 0.3 ± 0.03 in the second
rating repeated after two weeks.
Discussion: In this attempt, the teaching of the observers was limited
to an introduction to the general idea of the morphology grading
system and one example MRI image per category. The identification of
the dimension of the dural sac may be a difficult issue in absence of
complete T1 T2 MRI image series as it was the case here. The
similarity of the CSF to possibly present fat on T2 images was the
main reason of mismatch in the assignment of the cases to a category.
The Fleiss correlation factors of the five observers are fair and the
proposed morphology grading system is promising.