Anlysis of magnetic resonance neurography imaging features of the lumbosacral plexus in patients with far-out syndrome

English Keywords:Far-out syndrome  Magnetic resonance neurography  Nerve root entrapment  Lumbosacral plexus  Imaging diagnosis

English Abstract:

  【Abstract】 Objectives: To investigate the magnetic resonance neurography(MRN) imaging characteristics of lumbosacral plexus in patients with far-out syndrome(FOS) and their diagnostic value. Methods: 10 surgically confirmed FOS patients were retrospectively enrolled as the case group, and 10 asymptomatic volunteers were enrolled as the control group. No statistically significant differences in age or sex were found between the two groups(P>0.05). All subjects underwent lumbosacral plexus MRN. Qualitative indicators included L5 nerve root continuity, abnormal angulation of nerve root course, proximal crescent-shaped hyperintense edema, and low-signal cord compression sign at the pseudoarthrosis region were observed on MRN and compared. Quantitative measurements included standardized L5/S1 intervertebral disc height, nerve root-dural angle(NRA), and bilateral L5 nerve root cross-sectional area ratio(CSA ratio, calculated as affected side/unaffected side in the case group and larger side/smaller side in the control group). Statistical analyses were performed using independent samples t-test, Mann-Whitney U test, paired t-test, Fisher′s exact test, and Spearman′s rank correlation test. Results: In the case group, L5 nerve root discontinuity, proximal crescent-shaped hyperintense edema, and abnormal angulation were observed in all 10 patients, and low-signal cord compression sign at the pseudoarthrosis region was observed in 7 patients. In the control group, abnormal angulation was observed in 2 subjects, while none showed nerve root discontinuity, crescent-shaped edema, or low-signal cord compression sign. All qualitative indicators(nerve root discontinuity, abnormal angulation, and crescent-shaped edema) differed significantly between the two groups(P<0.001). The standardized L5/S1 intervertebral disc height in the case group was significantly lower than that in the control group[0.73(0.63, 0.77) vs 1.00(0.88, 1.12), P<0.001]. The NRA on the affected side was significantly smaller than that on the unaffected side in the case group(23.94°±3.88° vs 32.52°±4.32°, P<0.001), and was also significantly smaller than the left and right NRA of the control group(26.68°±1.77° and 26.70°±3.56°, respectively, both P<0.05). The CSA ratio in the case group was significantly higher than that in the control group(2.32±1.76 vs 1.11±0.65, P<0.001). Standardized intervertebral disc height was negatively correlated with abnormal angulation of nerve root course(rs=-0.850, P<0.001). Conclusions: In FOS patients, lumbosacral plexus MRN can directly demonstrate L5 nerve root discontinuity, proximal edema, and abnormal course in the extraforaminal region, and provide quantitative reference through NRA and CSA ratio.