Introduction and reproducibility of an updated practical grading system for lumbar foraminal stenosis based on high-resolution MR imaging

Abstract

In this paper we sought to develop and assess the reproducibility of an updated 6-point grading system for lumbar foraminal stenosis based on the widely used Lee classification that more accurately describes lumbar foraminal stenosis as seen on high-resolution MRI. Grade A indicates absence of foraminal stenosis. Grades B, C, D and E indicate presence of foraminal stenosis with contact of the nerve root with surrounding anatomical structures (on one, two, three or four sides for B, C, D and E respectively) yet without morphological change of the nerve root. To each grade, a number code indicating the location of contact between the nerve root and surrounding anatomical structure(s) is appended. 1, 2, 3 and 4 indicate contact of the nerve root at superior, posterior, inferior and anterior position of the borders of the lumbar foramen. Grade F indicates presence of foraminal stenosis with morphological change of the nerve root. Three readers graded the lumbar foramina of 101 consecutive patients using high-resolution T2w (and T1w) MR images with a spatial resolution of beyond 0.5 mm3. Interreader agreement was excellent (Cohen’s Kappa = 0.866–1). Importantly, 30.6%/31.6%/32.2% (reader 1/reader 2/ reader 3) of foramina were assigned grades that did not appear in the original Lee grading system (grades B and D). The readers found no foramen that could not be described accurately with the updated grading system. Thus, an updated 6-point grading system for lumbar foraminal stenosis is reproducible and comprehensively describes lumbar foraminal stenosis as seen on high-resolution MRI.

High-Resolution 3D versus Standard-Resolution 2D T2-Weighted Turbo Spin Echo MRI for the Assessment of Lumbar Nerve Root Compromise

“…The relationship between the nerve root and surrounding intervertebral foramen was classified by using the updated practical grading system for lumbar foraminal stenosis [7]. In brief, this is a 6-point grading system that is based on the widely used Lee classification [5].…”

“…Grade F indicates the presence of foraminal stenosis with morphological change and compression of the nerve root. A figure illustrating this grading system can be found elsewhere [7].…”

“…In patients with radiculopathy, MRI is considered the imaging modality of choice to visualize and evaluate the relationship between the nerve root and the lumbar foramen [5][6][7] and between the nerve root and the lateral recess [8].…”

“…High-resolution, submillimeter 3D acquisitions provide images with less partial volume effects compared to the original thick-sliced 2D sagittal acquisitions. Thus, the relationship between the nerve root and the surrounding structures within the lateral recess and within the foramen can potentially be identified more precisely [7].…”

“…Recently, a study has introduced a new practical grading system for lumbar foraminal stenosis as seen in high-resolution submillimeter T2w images [7]. Therein, the authors state that the original grading system by Lee et al is no longer suitable for the evaluation of high-resolution images as a far more complex relationship between the nerve root and the surrounding structures within the intervertebral foramen can be identified.…”