Lumbar spinal stenosis (grading)

Last revised by Francis Deng on 18 Mar 2024

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

There are multiple systems for grading lumbar spinal stenosis in the central zone. The simplest classification was proposed by Lurie and colleagues, based on the degree of compromise of the central zone as expressed in thirds 1. This system may be the most popular in the literature 2. Two other, more complex but nonetheless popular systems are based on the relationship of fluid and cauda equina nerve roots within the thecal sac, as described by Lee and Schizas 4,5. A relatively newer classification system, described by Miskin and Mandell, is a modification of the Schizas system 6.

These systems have been validated for interrater reliability across specialties 1,4,6-8. Both the qualitative degree of compromise of the central zone (as expressed in thirds by Lurie) and the relation of fluid and cauda equina (as expressed by systems such as that of Schizas) were identified in a multidisciplinary international consensus conference as core items for a structured radiological report in patients with lumbar spinal stenosis 9.

The Lurie grading system defines central zone stenoses in thirds based on axial T2-weighted images 1. Although not named as such, a similar scheme has been endorsed in the "Lumbar disc nomenclature: version 2.0" recommendations of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology 3. The grades of stenosis are as follows:

  • none

  • mild: compromise of the area of ≤1/3 of its normal size

  • moderate: compromise of the area between 1/3 and 2/3 of normal size

  • severe: compromise of the area of >2/3 of normal size

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 4:

  • 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 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 5:

  • 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 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 6:

  • 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

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