Correlation between MRI Grading System and Surgical Findings for Lumbar Foraminal Stenosis

Abstract

Objective: Magnetic resonance imaging (MRI) grading systems using sagittal images are useful for evaluation of lumbar foraminal stenosis. We evaluated whether such a grading system is useful as a diagnostic tool for surgery.

Methods: Between July 2014 and June 2015, 99 consecutive patients underwent unilateral lumbar foraminotomy for lumbar foraminal stenosis. Surgically confirmed foraminal stenosis and the contralateral, asymptomatic neuroforamen were assessed based on a 4-point MRI grading system. Two experienced researchers independently evaluated the MR sagittal images. Interobserver agreement and intraobserver agreement were analyzed using κ statistics.

Results: The mean age of patients (54 women, 45 men) was 62.5 years. A total of 101 levels (202 neuroforamens) were evaluated. MRI grades for operated neuroforamens were as follows: Grade 0 in 0.99%, Grade 1 in 5.28%, Grade 2 in 14.85%, and Grade 3 in 78.88%. Interobserver agreement was moderate for operated neuroforamens (κ=0.511) and good for asymptomatic neuroforamens (κ=0.696). Intraobserver agreement by reader 1 for operated neuroforamens was good (κ=0.776) and that for asymptomatic neuroforamens was very good (κ=0.831). In terms of lumbar level, interobserver agreement for L5-S1 (κ=0.313, fair) was relatively lower than the other level (κ=0.804, very good).

Conclusion: MRI grading system for lumbar foraminal stenosis is thought to be useful as a diagnostic tool for surgery in the lumbar spine; however, it is less reliable for symptomatic L5-S1 foraminal stenosis than for other levels. Thus, various clinical factors as well as the MRI grading system are required for surgical decision-making.

Keywords: Foraminotomy; Lumbar vertebrae; Magnetic resonance imaging; Spinal stenosis; Surgery.

Fig. 1

Four-point-scale for grading of lumbar foraminal stenosis in sagittal MRI suggested by Lee et al.. A: Grade 0 (normal). Sagittal cross section through foramen shows normal neuroforamen. B: Grade 1 (mild foraminal stenosis). Sagittal cross section through foramen shows perineural fat obliteration in two opposing directions (vertical or transverse, arrows). C: Grade 2 (moderate foraminal stenosis). Sagittal cross section through foramen shows perineural fat obliteration in four directions (arrows). D: Grade 3 (severe foraminal stenosis). Sagittal cross section through foramen shows morphologic changes in the nerve root. MRI: magnetic resonance imaging.

Fig. 2

T1-weighted sagittal image of a 44-year-old man with left lower extremity pain. A: Sagittal MR image shows Grade 3 foraminal stenosis at left foramen of the L3–L4 level. B: Sagittal MR image shows Grade 0 of normal neuroforamen at right foramen of the L3–L4 level. MR: magnetic resonance.