Bulking agent is used in the treatment of female stress urinary incontinence. There has been wide variability in reported success rates, ranging from 29.8% to 89.7% in the short term and from 42%  to about 70% in the long term.  Failure of the procedure may be related to the patient and the severity  of urinary incontinence, or to technical problems. The aim of our study is to evaluate by trans labial  ultrasonography whether there are factors that can explain bulking agent failure.

Our prospective study was conducted in a level III urogynecologic center on women undergoing transurethral infiltration of bulking agent (Bulkamid®,PAHG).It was accepted by the bioethics  committee and all patients signed an informed consent. We included:women between 18 and 80  years of age with mild to moderate stress urinary incontinence. We excluded: women undergoing  previous anti incontinence surgery, POP stage >II, neurogenic bladder.Preoperative evaluation  included: urogynecological examination, dynamic translabial ultrasound, and urodynamic test. 
Patients were evaluated at 1,3,6,12 months after surgery and then annually. Ultrasound was repeated at 6 months.It was performed at rest and after Valsalva manoeuvre. We used a 3.5-5 MHz  curved array probe that was placed between the labia. The position of the PAHG along the urethra was determined with respect to the length of the urethra. A bulking agent was considered “proximal” 
if it was located along the first 0-40% of the urethra, measured from the bladder neck. The bulking  agent was “mid-urethral” if it was located along the second 40-60% of the urethra and “distal” if it  was located along the last 60-100%.  Statistical analysis :Chi-square test, Fisher's exact test; Logistic regression model and odds ratios (with 95% confidence intervals); p < 0.05 was statistically significant

50 consecutive patients underwent PAHG were analysed. The mean follow-up was 15±2.4 months. The objective cure rate was 84% 
 (42 patients) one month after surgery, 56% (28 patients) at 6  months and 36% (18 patients) at the last visit. Incontinent women had PAHG in a more distal position  (70% vs 4.2%, p<0.0001; OR 65.10 (10.12-376.49)) and with an oblong shape (65% vs 3.4%, p<0.0001OR: 93 (13.16-524.11)) compared with continent women who had a spherical shape and  proximal position. Incontinent women had persistent open bladder neck (78% vs 10.2%, p<0.0001, OR: 5.88 (1.51-17.89).Multivariate logistic regression analysis showed that a distal PAHG position (2.42 (0.02-0.54) p= 0.03) and open bladder neck (5.23 (0.11-0.37)p<0.0001) were risk factors for 
PAHG failure. The shape of PAHG was not confirmed as a risk factor (1.86 (0.15-0.0008)p=0.07).

Probably the location of PAHG facilitates the mechanism of action, improving urethral coaptation and restoring continence. The bladder neck closure assists in achieving the goal.

This study shows that a PAHG performed close to the bladder neck such that it is closed results in 
a better long-term outcome.