Clinical Correlation of a New MR Imaging Method for Assessing Lumbar Foraminal Stenosis

Case Selection

Our study population included 49 (54%) men and 42 (46%) women who visited our institution and underwent MR imaging of the L-spine between January 2010 and September 2010. The age distributions were the following: Forty-nine patients were younger than 50 years (54%), and 42 patients were (46%) older. The mean age was 50.6 years. Exclusion criteria were the following: infection, tumor, acute trauma, surgical history, central disk herniation, combined brain infarction, or other intracranial lesions and peripheral neuropathy. Patients with symptoms at different cord levels or on opposite sides were excluded. This retrospective study was approved by the institutional ethics review board, with no requirement for informed patient consent.

Image Analysis

MR imaging examinations were interpreted by 2 fellowship-trained academic musculoskeletal radiologists who had 12 and 10 years of experience. They were blinded to the clinical information and radiologic reports. A total 728 foramina and corresponding nerve roots in 91 patients were qualitatively analyzed from L2–3 to L5–S1. The radiologists assessed the presence and grade of lumbar foraminal stenosis at the maximal narrowing point according to the new grading system suggested by Lee et al.³ We named this grading system the “Lee system.” Lumbar foraminal stenosis was classified in the Lee system on the basis of the T1-weighted sagittal images as follows: grade 0 = absence of foraminal stenosis, grade 1 = mild foraminal stenosis showing perineural fat obliteration surrounding the nerve root in 2 opposing directions without morphologic change of the nerve, grade 2 = moderate foraminal stenosis showing perineural fat obliteration surrounding the nerve root in 4 directions without morphologic change of the nerve, and grade 3 = severe foraminal stenosis showing nerve root collapse or morphologic change. When the radiologists were not confident about their findings, the T2-weighted sagittal and axial images were used as a supplementary evaluation method.

We could exclude the possibility of partial volume artifacts of the lesion from the nerve root itself and could trace the full course of the nerve root through the T2-weighted images. The T2-weighted axial image was especially useful in the evaluation of perineural cysts or nerve root swellings that can cause false-positive results. The radiologists also assessed the foraminal stenosis with the Wildermuth grading system (Wildermuth system) on the basis of the T1-weighted sagittal images. The severity of foraminal stenosis was graded 0 if the foramina were without pathology (normal dorsolateral border of the intervertebral disk and normal form at the foraminal epidural fat); grade 1 if slight foraminal stenosis and deformity of the epidural fat were seen, with the remaining fat still completely surrounding the exiting nerve root; grade 2 if marked foraminal stenosis with epidural fat only partially surrounding the nerve root was seen; and grade 3 for advanced stenosis with obliteration of the epidural fat.

Clinical Correlation

Neurologic examinations were performed and clinical manifestations were acquired by the same physician. We considered neurologic clinical manifestations as observed paresthesia, extremity weakness, numbness, and funicular or radicular pain. Positive neurologic signs were a positive Lhermitte sign, Spurling sign, decreased response of DTR, and a positive denervation sign on EMG. DTR evaluations were performed in all patients, and EMG was performed in 5. More than 1 positive neurologic sign combined with >1 neurologic clinical manifestation was considered a PNM of the lumbar foraminal stenosis. Symptoms of upper extremities or the opposite side of the stenosis were not considered PNMs.

MR Imaging Parameters

All MR imaging examinations were performed by using the same protocol with a 1.5T magnet (Intera; Philips Healthcare, Best, the Netherlands) by using a Syn-Spine coil (Philips Healthcare) and fast spin-echo imaging. T1-and T2-weighted images were obtained in the axial plane, and T1- and T2-weighted images and T2 STIR images were obtained in the sagittal plane in supine position. An FOV of 32 cm, matrix 512 × 256, and section thickness of 4 mm were used for sagittal views; an FOV of 15 cm, matrix 256 × 320, and section thickness of 4 mm were used for axial images. MR images were sagittal T1-weighted spin-echo (TR/TE = 500–600/12–17 ms), T2 STIR (TR/TE = 2500/60 ms), T2-weighted (TR/TE, 3500/120 ms), axial T2-weighted turbo spin-echo (TR/TE, 3000–4000/60 ms), and T1-weighted turbo spin-echo (TR/TE, 600–700/10–15 ms).

Statistical Analysis

Interobserver agreement between the 2 radiologists was analyzed by using κ statistics. κ value interpretation was the following: poor (κ < 0.1), slight (0.1 ≤ κ ≤ 0.2), fair (0.2 < κ ≤ 0.4), moderate (0.4 < κ ≤ 0.6), substantial (0.6 < κ ≤ 0.8), and almost perfect (0.8 < κ ≤ 1). Rs were calculated with categoric regression analysis and nonparametric correlation analysis (Spearman correlation). For analysis of the relationship between findings and patient characteristics, the association of the MR imaging findings and clinical manifestations was evaluated by age (younger than 50 years, equal to or older than 50 years). R between 0.7 and 0.9 was considered a relatively high correlation, and R > 0.9 was a very high correlation. The level of correlation significance was .01. Statistical analyses were performed by using the Statistical Package for the Social Sciences software, Version 10.1 (SPSS, Chicago, Illinois).