Lumbar Thecal Sac Dimensions and Axial Spinal Cord Areas on Magnetic Resosnace Imaging in 626 Healthy Subjects.

Methods: A cross-sectional study. Objective: The aim of this study was to investigate the lumbar thecal sac dimensions and spinal cord area on magnetic resonance (MR) imaging in healthy volunteers.

Background: There are few reports regarding lumbar spine MRI in healthy subjects, and the difference in spinal canal dimensions by age remains unclear.

Methods: A total of 629 healthy volunteers were enrolled, including ≥50 males, females, and subjects in each of the 20s to 70s age decades. The anteroposterior and transverse diameters of the thecal sac and axial areas of the thecal sac and spinal cord were measured at the disc levels on T2-weighted axial MR images. The anteroposterior-to-transverse ratio of the thecal sac (APTR) was calculated.

Results: The thecal sac area from T12/L1 to L4/5 was reduced in older age group, but there was no significant difference in L5/S1. The thecal sac area was significantly reduced in older age group: 89.9%, 86.0%, 84.6%, 80.3% at T12/L1, L1/2, L2/3, and L3/4, respectively, and 79.9% at L4/5 in subjects in their 70 s relative to that in subjects in their 20 s. The APTR was significantly reduced in older age group from T11/12 to L2/L3 in males and at T10/11, L3/4 and from T11/12 to L2/3 in females. Narrow thecal sac areas <80 mm2 were found in 10 subjects. The spinal cord area was significantly reduced in older age group at T10/11 in males and at T9/10, T10/11, and T11/12 in females. The area was 92.0% at T10/11 in subjects in their 70s relative to the area of subjects in their 20s.

Conclusions: The thecal sac area was reduced in older age group from T12/L1 to L4/5, and the thecal sac area was reduced in the anteroposterior and all directions in the upper and lower lumbar area in age group, respectively. Approximately, 3.0% of healthy population in their 50s or older will have severe asymptomatic stenosis.Level of Evidence: 2.