Lumbosacral plexus root thickening: Establishing normal root dimensions using magnetic resonance neurography.

Disorders affecting the lumbosacral plexus (LSP) can alter root diameter. Our aim was to determine normal LSP nerve root dimensions using magnetic resonance neurography (MRN). Eleven asymptomatic patients (ages: 18-53, mean: 34 years) underwent MRN of the LSP on a 3 T scanner with an 8-channel torso-PA coil. IDEAL T2-weighted images were acquired and nerve root dimensions were measured from the second lumbar (L2) to the first sacral (S1) vertebrae on the coronal plane, 5 mm from the dorsal root ganglion (DRG). Root size was recorded by three separate groups of radiologists with different levels of expertise. Additional LSP-MRN images were acquired from a fresh-frozen cadaver specimen using the same scanner and parameters identical to those described above. Subsequently, two experienced anatomists dissected and measured the LSP roots at exactly the same distance from the DRG, using an electronic caliper. Mean root size values recorded (± standard deviation) in the asymptomatic patients were as follows: L2: 3.12 mm (±0.92), L3: 4.29 mm (±0.95), L4: 5.13 mm (±0.79), L5: 5.29 mm (±0.9), and S1: 5.38 mm (±0.7). The correlation coefficients were 0.72 between the patient and cadaver MRN results and 0.79 between the patient and dissected cadaver MRN results. Inter-observer agreements were 0.73 among the radiologist groups and 0.87 between the anatomists conducting dissections. We believe MRN provides reliable assessments of LSP root thickness. More extensive studies should be conducted to confirm the results described here. Clin. Anat. 31:782-787, 2018. © 2018 Wiley Periodicals, Inc.