Internal tangential circular area method for the evaluation of central lumbar spinal canal stenosis

Objective:To investigate the diagnostic value of internal tangential circular area (CA) in CT scan for central lumbar canal spinal stenosis. Methods:CT scanning from L2 to L5 was performed for 200 normal people and 183 patients with central spinal stenosis. There are 5 layers at every intervertebral space and 1 layer at the upper one-third of every pedicle which is vertical to spine. The layer thickness and layer interval both are 3 mm. The following measurements were conducted with soft tissue window: the internal tangential circular area of soft spinal canal at the intervertebral space (AIV) and the upper corresponding space of pedicle(AV). Results:① The normal value of AIV,AV were expressed by mean ±standard deviation, and respectively they were (153.1±33.8)mm2, (152.6±34.1) mm2. The lower borderline of AIV, AV were 97.7mm2 and 96.7mm2 respectively; ② AIV at different levels showed no significant differences, neither did AV (P0.05). The differences between AIV and AV weren't statistically significant. So AIV and AV were combined by CA, which means spinal canal area. The normal value of CA was (152.8±34.0)mm2, and the lower borderline of CA was 97.0 mm2; ③ 322 surgery-confirmed spinal stenosis levels were analysed according to the lower borderline of MSD and CA. The coincidence of MSD for central spinal stenosis 83.8% and the coincidence of CA for central spinal stenosis was 94.1%, which was higher than MSD.Conclusion:CA was recommended as the first selection in diagnosing central spinal stenosis because of its simple operation and high accuracy rate.