Aetiology

The urethral sphincter is situated at the region of the bladder neck and proximal two-thirds of the urethra. It contributes about 50% of the total urethral resistance.

Stress urinary incontinence occurs when the proximal urethra drops below the pelvic floor because of pelvic relaxation defects. Intra-abdominal pressure is no longer transmitted equally to the bladder and proximal urethra.

This situation is most frequent: (1,2)

• following childbirth - pregnancy, labour and delivery may all cause mechanical and denervation injury to the normal supports of the bladder neck and proximal urethra
• after the menopause - decreased intraurethral pressure due to oestrogen lack

Imperfect sphincter control also complicates epispadias which show a widened bladder neck, shortened urethra and separation of the symphysis pubis.

Reference

1. Aoki Y, Brown HW, Brubaker L, et al. Urinary incontinence in women. Nat Rev Dis Primers. 2017 Jul 6;3:17042.
2. National Institute for Health and Care Excellence. Urinary incontinence and pelvic organ prolapse in women: management. NG123. Last updated June 2019.