The tension- free vaginal tape (TVT) is now used worldwide for the surgical treatment of Genuine Stress Inconti-nence (GSI). Based on the "Integral Theory" (1), it is assumed that the TVT  replaces defective ligamentous and muscular structures to restore normal anatomy and provide for midurethral "functional kinking". However, objective data so far is scarce (2). To elucidate the mode of action of the TVT, we assessed anatomy and function by ultra-sound imaging and flowmetry and correlated this data with symptoms.

 

Methods

46 consecutive patients were seen on average 0.72 years (6w- 1.4 yrs) after TVT. Preoperative detrusor instability was not an exclusion criterion. A standardized questionnaire was filled in and a clinical stress test performed with a subjectively full bladder (median 367 ml). Translabial ultrasound was performed erect with a full bladder for documentation of stress leakage on colour Doppler (3) or clinical stress test. The patient was then asked to void for flowmetry.

 

Ultrasound was repeated  supine to determine tape position and mobility. The TVT is strongly hyperechoic and easily observed on ultrasound. On Valsalva, images were taken and the position of  bladder neck and superior tape margin determined relative to the inferoposterior symphyseal margin. Symptoms, Doppler/ stress test results and flowmetry data were compared with 1.) tape position relative to the internal urethral meatus,  2.) tape position relative to the symphysis pubis, and  3.) tape mobility on Valsalva.

 

Results

Table 1 gives symptoms and signs after average followup of 0.72 years. Table 2 summarizes bladder neck and tape position and mobility data; Table 3 correlates this data with incontinence and flowmetry. Compared to preoperative flowmetry, postoperatively the maximum and mean flow rates had dropped an average of 22 (p<0.0001) and 23 centiles (p<0.0001). A tight tape reduced the incidence of recurrent stress incontinence but also correlated moderately (r= 0.313, p= 0.034) with low maximum flow rate centiles. The lowest average flow rate centiles were seen with tapes that were close to the bladder neck in the horizontal plane, and remained above the symphysis on valsalva (p= 0.026).

 

	preop. n                       %	Postop n                      %
Stress Incontinence Urge Incontinence Hesitancy/ poor stream Dry on Stress Test/ Doppler	46                     100 16*                    38 not available 0                        0	9                       20 23                     50 24                     52 41                     89

 

Table 1: Symptoms and signs before and after TVT placement (n= 46, *n=42)

Bladder neck descent Urethral rotation Funnelling (n) Tape position rel. to symphysis (stress) Tape mobility on Valsalva (total)

2.2 cm 57.4 deg 29 -0.5 cm 1.9 cm

(0- 4.8) (10- 120) (63%) (1.5- -2.4) (0.7-  4.2)

 

Table 2: Bladder neck and TVT position and mobility data (n= 46). Means, range in parentheses

 

	SI	Max. flow rate centile
Tape tightness (horiz. dist. to bladder neck) Tape tightness (horiz. dist. to symphysis) Tape position (vert. dist. to symphysis (stress) Tape mobility on Valsalva (horizontal) ”Pinching” on Valsalva	n.s p= 0.008 p= 0.004 p= 0.036 p< 0.00001	p= 0.034 n.s n.s. p= 0.087 n.s.

Table 3: Correlation between tape position and mobility and postoperative incontinence and maximum flow rate (n= 46). All correlations are positive except for ”pinching”.

 

Conclusion

 

The TVT has a high cure rate for stress incontinence (SI). Both in success and failure it resembles traditional slings.

It seems to be an obstructive procedure. Ultrasonic findings vary depending on dissection, placement, tensioning and coexisting cystourethrocele. In many patients hypermobility persists, and continence seems to be achieved by a kinking effect, with the urethra rotating horizontally and being compressed against and kinked around the tape. Often there is no effect on the bladder neck, as shown by  a high incidence of funnelling. A ”loose” tape seems to increase the risk of recurrent SI. ”Tight” tapes, on the other hand, compress the urethra against the symphysis pubis (a ”pinching” effect), potentially causing increased obstruction but making recurrence of  SI highly unlikely.

 

Both position and mobility of the TVT vary considerably, and this variability  seems to influence outcome. There is a need for further research regarding a reproducible tightening mechanism.

 

References

1 Acta Obstet.Gynecol.Scand.Suppl. 153:7-31, 1990.

2 Br.J.Obstet.Gynaecol. 106(4):345-350, 1999.

3 Ultrasound.Obstet.Gynecol. 14:144-147, 1999.