Purpose: Although high resolution MRI can play a critical role in the evaluation of diseases affecting the female urethra, normative values have not been established. In this retrospective study, the normal values for female urethral dimensions and its supportive structures were measured and compared using a body coil (BC) and endorectal coil (ERC), and correlated with age and menopause.
Material and methods: BC and/or ERC images of the pelvis in 20 patients (ages 27-82) with confined cervical cancer (stage IB or less) were reviewed. None of the patients had a history of urinary symptoms, pelvic prolapse, pelvic radiation, or prior bladder or urethral surgery. Images evaluated included axial and/or sagittal T2 weighted SE images of the lower pelvis before and/or after endorectal coil placement. Several measurements including urethral and bladder dimensions were obtained independently by two radiologists and compared statistically. Calculated urethral volume was correlated with the patients' age and menopausal status. The impact of calculated bladder volume on urethral dimensions was evaluated. Additional measurements of contiguous supporting structures were also correlated with age.
Results: Inter-rater reliability showed a strong intra-class correlation (95% CI) for urethral dimensions. A statistically significant difference between raters was only noted for the right pubovesical ligament measurement. Inter-technique reliability was also strong (95% CI) except for the distal transverse urethral dimension. Bladder volume did not effect measurement of urethral dimensions (p > .39). Lastly, calculated urethral volume utilizing the ERC technique showed an inverse correlation with age (p < 0.05) and with the BC a correlation with menopausal status (p < 0.05).
Conclusions: Measurement of urethral dimensions by either ERC or BC MRI is reliably reproducible by independent radiologists. There is no need for standardization of bladder volumes during urethral MRI. Normative values for all measured angles and dimensions are presented. There is evidence of correlation of urethral volume with age and menopause, though a larger study is warranted.