Physiological pseudo-thickened cauda equina associated with dural sac dilatation on magnetic resonance imaging

Objectives In daily clinical practice, the assessment of the thickness of the cauda equina on lumbar spine magnetic resonance imaging is an important parameter. However, its relevance to the size of the dural sac in non-pathological conditions is unknown. To examine the relationship between the size of the dural sac and the apparent thickness of the cauda equina nerve root using lumbar spine magnetic resonance imaging in non-pathological conditions. Methods We retrospectively measured the dural sac diameter and vertebral body diameter, counted the apparent number, and calculated total cross-sectional area of the cauda equina, dural sac ratio and the area of one apparent nerve root of cauda equina in 100 cases. Spearman's rank correlation coefficient ( ρ) was used. Results Dural sac ratio and diameter were positively correlated with the area of one apparent nerve root ( ρ=0.77, P<0.001; ρ=0.74, P<0.001; respectively) and negatively correlated with the apparent number of cauda equina in a single cross-section ( ρ=–0.63, P<0.001; ρ=–0.52, P<0.001; respectively). Conclusions A larger dural sac ratio and diameter was associated with an apparently thicker cauda equina and lower visible number. In a larger dural sac, the physiologically clumped and apparently thicker cauda equina should not be misdiagnosed as pathological.