Sagittal Normal Limits of Lumbosacral Spine in a Large Adult Population: A Quantitative Magnetic Resonance Imaging Analysis

Objectives: The objective of this study was to determine, using magnetic resonance imaging (MRI) of the lumbosacral spine from L1 to S1, the values of the normal sagittal diameter of the spinal canal (SCD), sagittal diameter of the dural sac (DSD), and the normal values of dural sac ratio (DSR) in a large nonsymptomatic adult population and to discriminate whether a vertebral canal is pathological or nonpathological for dural ectasia and/or stenosis. Materials and Methods: Six hundred and four patients were prospectively enrolled. All measurements were performed on MRI sagittal T1- and T2-weighted images. The 95% confidence interval (95% CI), defined as mean ± 1.96 standard deviation, was determined for each metric. The upper limit of 95% CI was considered the cutoff value for the normal DSR; the lower limit of 95% CI was considered the cutoff value for the normal SCD. Results: SCD cutoff values from L1 to S1 ranged from 14.5-10.1 mm (males) to 15.0-9.9 mm (females). DSD ratios at S1 and L4 level show a significant difference in male and female groups: 11% of S1/L4 values exceeded 1 in male group while only 4% of S1/L4 values exceeded 1 in female group. Mean DSR at each level was significantly higher in female patients than in male patients (P < 0.001), ranging from 0.70 to 0.56 (male) and from 0.82 to 0.63 (female). Conclusions: We determined the cutoff values for the normal DSR and for the normal SCD. Our findings show the relevant discrepancies with respect to literature data for diagnosis of lumbar stenosis and/or dural ectasia.