The 'iris effect': how two-dimensional and three-dimensional ultrasound can help us understand anti-incontinence procedures.

OBJECTIVE

The objective of this prospective, observational study in patients after tension-free vaginal tape (TVT) implantation was to describe the spatial relationship between suburethral sling implants, urethra and bony pelvis with the help of translabial two-dimensional and three-dimensional (3D) ultrasound.

METHODS

A total of 141 women were examined by translabial ultrasound, supine and after voiding. The TVT sling is highly echogenic and easily identified posterior to the urethra. Tape location was described in the mid-sagittal plane relative to bladder neck and inferoposterior symphyseal margin, at rest and on Valsalva maneuver. In a subset of 83 women, 3D volume ultrasound was performed.

RESULTS

The cranial tape margin was situated on average 9.3 mm above and 16.5 mm posterior to the symphyseal margin (Valsalva: 3.9 mm below and 9.6 mm behind the symphysis); the average tape movement on Valsalva was 16 (range, 2-34.2) mm. The distance between tape and inferoposterior symphyseal margin narrowed highly significantly from 20.4 +/- 4.3 mm at rest to 12.9 +/- 3.9 mm on Valsalva (P < 0.001). When a fitted line plot was placed through tape coordinates on an x-y coordinate system, it became evident that tape movement occurs in an arc around the fulcrum of the posterior symphysis pubis. The result is an increasing reduction in the gap between tape and symphysis pubis (termed the 'iris effect'), implying mechanical compression of the urethra.

CONCLUSIONS

The curative effect of the TVT on stress incontinence is likely to be due to mechanical compression of the urethra between implant and symphysis pubis. A large variation in tape location and movement explains its wide margin of clinical safety and efficacy.