Standardization and validation of a novel and simple method to assess lumbar dural sac size.

•DSD (L1-L5) does not differ in the AP or TR plane by gender, height, or age.•AP- and TR-DSD measures correlate well between readers with different experience.•Height is positively correlated to AP-VBD in both males and females.•Varying vertebral body size distorts dural sac size assessment when using ratios.•Compared to DSR, AP-DSD discriminates better between control and Marfan subjects.