Lumbar spinal stenosis (grading)

Lumbar spinal stenosis grading refers to systems for classifying the severity of central spinal canal narrowing around the cauda equina nerve roots. 

Usage

The two most popular systems, both applied to visual assessment of MRI, are the Lee grading system, and the Schizas grading system. Both these systems have been found to be reliable, having high inter-observer agreement ^1-3.

A relatively newer classification system, the Miskin classification system, has been shown to reduce inter-subspecialty variability between neuroradiologists and musculoskeletal radiologists ⁴.

Classification

Lee grading system

Lee et al. reported a 4-grade classification of lumbar central canal stenosis based on the obliteration of CSF space in front of the cauda equina in the dural sac using axial T2-weighted images ¹:

• grade 0 (no stenosis): the anterior CSF space is not obliterated
• grade 1 (mild stenosis): the anterior CSF space is mildly obliterated but all cauda equina can be clearly separated from each other
• grade 2 (moderate stenosis): the anterior CSF space is moderately obliterated and some of the cauda equina are aggregated (impossible to visually separate)
• grade 3 (severe stenosis): the anterior CSF space is severely obliterated so as to show marked compression of the dural sac and the cauda equina appears as one bundle (none can be visually separated from each other)

Schizas grading system

Schizas et al. reported a 7-grade classification of lumbar spinal stenosis based on the morphology of the dural sac and ratio of rootlets to CSF on axial T2-weighted images ²:

• grade A (no or minor stenosis): CSF is clearly visible in the dural sac but the distribution is heterogeneous
  • A1: rootlets lie dorsally, occupying less than half the dural sac area
  • A2: rootlets lie dorsally, in contact with the dura and in a horseshoe configuration
  • A3: rootlets lie dorsally, occupying more than half the dural sac area
  • A4: rootlets lie centrally, occupying more than half the dural sac area
• grade B (moderate stenosis): rootlets occupy the whole of the dural sac but they can still be individualized; some CSF is still present, giving a grainy appearance to the sac
• grade C (severe stenosis): no rootlets are recognized; no CSF is visible, giving a homogeneous gray signal to the sac, while epidural fat remains posteriorly
• grade D (extreme stenosis): in addition to no rootlets being recognizable, the epidural fat posteriorly is obliterated

Miskin-Mandell grading system

Miskin et al. reported a 4-grade classification system, modified from the Schizas et al. grading system, after multidisciplinary consultation with both radiologists and non-radiologist spine expert physicians and surgeons ⁵:

• normal: nerve roots are freely distributed, without crowding; the anterior margin of the thecal sac is flat or convex
• mild spinal stenosis: slight crowding of the nerve roots; the anterior margin of the thecal sac is flat or slightly concave; the nerve roots remain distinguishable from the CSF
• moderate spinal stenosis: crowding of the nerve roots, resulting in a homogeneously “speckled” appearance of CSF interspersed with nerve roots; the anterior margin of the thecal sac is concave
• severe spinal stenosis: complete effacement of CSF, resulting in nerve roots being not individually distinguishable; the anterior margin of the thecal sac is concave or not discernable