Introduction: Measures of the degree of lumbar spinal stenosis (LSS)
such as antero-posterior diameter of the canal, and dural sac cross
sectional area vary, and do not correlate with symptoms or results of
surgery. We created a grading system, comprised of seven categories,
based on the morphology of the dural sac and its contents as seen on
T2 axial images. The categories take into account the ratio of rootlet/
CSF content. Grade A indicates no significant compression, grade D
is equivalent to a total myelograhic block. We compared this classification
with commonly used criteria of severity of stenosis.
Methods: Fifty T2 axial MRI images taken at disc level from 27
symptomatic LSS patients undergoing decompressive surgery were
classified twice by two radiologists and three spinal surgeons working
at different institutions and countries. Dural sac cross-sectional surface
area and AP diameter of the canal were measured both at disc
and pedicle level from DICOM images using OsiriX software. Intraand
inter-observer reliability were assessed using Cohen's, Fleiss'
kappa statistics, and t test.
Results: For the morphological grading the average intra-and inter
observer kappas were 0.76 and 0.69+, respectively, for physicians
working in the study originating country. Combining all observers the
kappa values were 0.57 ± 0.19. and 0.44 ± 0.19, respectively. AP
diameter and dural sac cross-sectional area measurements showed no
statistically significant differences between observers. No correlation
between morphological grading and AP diameter or dural sac crosssectional
areawas observed in 13 (26%) and 8 cases (16%), respectively.
Discussion: The proposed morphological grading relies on the identification
of the dural sac and CSF better seen on full MRI series. This
was not available to the external observers, which might explain the
lower overall kappa values. Since no specific measurement tools are
needed the grading suits everyday clinical practice and favours
communication of degree of stenosis between practising physicians.
The absence of a strict correlation with the dural sac surface suggests
that measuring the surface alone might be insufficient in defining LSS
as it is essentially a mismatch between the spinal canal and its contents.
This grading is now adopted in our unit and further studies
concentrating on relation between morphology, clinical symptoms
and surgical results are underway.