Evaluation of the female bladder neck and urethra using MRI with fiber tractography: Prospective study on a large cohort of continent women.

Aims: To prospectively evaluate the performance of a last generation magnetic resonance imaging (MRI) device with tractography to identify the normal female urethral sphincters in terms of morphology and quantification on a large cohort of continent women.

Methods: We have recorded the data of 75 continent women who underwent a diffusion tensor imaging (DTI) sequence with fiber tractography during a pelvic MR examination. Three groups of age were analyzed in terms of color fiber tracking quality and quantitative parameters (fractional anisotropy [FA] and mean diffusibility [MD]). Statistical analysis was done for the qualitative assessment using weighted kappa statistics of Cohen and for the quantitative parameters using a non-parametric Kruskal-Wallis test.

Results: For all cases, fiber-tracking resulted in a satisfactory representation of the complexity of the orientation of the fibers. The interobserver concordance of qualitative data was substantial, calculated at 0.78 (confidence interval: 0.71-0.85). For FA, there was no statistically significant difference with the age between the three urethral segments (p > 0.05). However, we registered a significant difference inside each group between the different segments (p < 0.05), corresponding to different orientation of fibers. For MD, we have found a statistically significant difference both between levels inside each group and according the age, meaning a variation of the water mobility for each type of musculature and with age (p < 0.05).

Conclusion: DTI with fiber tractography performed on a recent MR unit is a robust method for the three-dimensional visualization of the details and connections of the urethral female sphincters. Quantitative variations with age need to be considered.