Female urinary incontinence: pathophysiology, methods of evaluation and role of MR imaging

Urinary incontinence (UI) is one of the most common conditions that cause a significant psychosocial and hygienic problem in an aging female population. In this article we focus on the sphincteric type of stress UI in women, review the anatomy of the urethral sphincter and its support mechanism, and discuss methods of the evaluation of urethral function. Stress UI is the functional consequence of an anatomical abnormality, urethral hypermobility (UH) and intrinsic sphincter deficiency (ISD). Imaging plays an adjunct role to urodynamics in the assessment of women with UI. MR imaging due to its superior soft tissue contrast resolution contributes many findings that are predictive of UH, such as abnormal descent of the bladder neck, disruption of periurethral ligaments and vaginal attachments, and defects within the levator ani muscle. In ISD, MR imaging may show foreshortening or thinning of the sphincter muscle and bladder neck insufficiency manifested by funneling. MR imaging is ideal to evaluate the anatomy of the bladder neck and urethra; functional implications correlate well with functional studies and make MR imaging central to understanding the causes of stress UI and its thorough evaluation.