Diffusion-weighted magnetic resonance imaging for the diagnosis of patients with lumbar nerve root entrapment syndromes: results from a pilot study

Lumbar nerve root entrapment syndromes cause radicular signs and symptoms in the affected leg. The applicability of diffusion-weighted imaging (DWI) for the assessment of lower lumbar nerves (L4-S1) has been demonstrated. The purpose of this pilot study was to establish DWI reference data for the all lumbosacral nerve roots (L1-S1) in a healthy, asymptomatic study population and to determine its potential as a diagnostic tool for patients with lumbar radicular syndromes. 20 asymptomatic healthy volunteers were included (average age 39 years (24-59 years; n = 10 female, n = 10 male). The lumbosacral spine was scanned twice in a standardized fashion (1.5 T Magnetom Avanto and 3 T Magnetom Skyra, Siemens AG Healthcare, Erlangen, Germany). A spin-echo type echo-planar (SE-EPI) sequence was used to determine axial ADC maps and measurements (length, width, and angulation) of the dorsal root ganglion (DRG) and distal spinal nerves (DSN). Disc pathology, lumbar foraminal stenosis and nerve root compromise were classified. Using 3 T images 218 (91 %) lumbar nerve roots had no pathologic finding [1.5 T: 226 (94 %)]. All DRG and DSN could be visualized and identified on axial apparent diffusion coefficient (ADC). On average we measured ADC values of 1,231 mm(2)/s (SD 308 mm(2)/s) at the DRG for the 1.5 T scanner and 1,756 mm(2)/s (SD 465 mm(2)/s) for the 3 T scanner. There were no statistically significant gender or side differences in the 1.5 and 3 T images (p > 0.05). We noted an increase of the ADC values starting from cranial (L1: 1,444 mm(2)/s) to caudal (S1: 1,918 mm(2)/s). The average ADC value at the DSN was 1,018 mm(2)/s for the 1.5 T scanner compared to 1,589 mm(2)/s for the 3 T scanner (p < 0.001). For the first time, we have established data for the DRG and DSN in human lumbosacral spinal nerves (L1-S1), using diffusion-weighted magnetic resonance imaging techniques. 3 T ADC maps have a higher signal to noise ratio, thus offering better image quality. Results from this study suggest that DWI has added value as new diagnostic tools for patients with symptomatic lumbar nerve root entrapment syndromes as well.