This study found that the volume of injected PAHG was reduced significantly 3 months after surgery. In contrast to some previous histological studies [7, 8], which stated that PAHG injections remain stable in volume for years, we found a mean 36.5% loss in bulking agent volume during the study period. The only study by Mouritsen et al. [9] described volume of injected PAHG in eleven women at eight years follow-up. The deposits had a volume of 0.14–2.44 cm³. In our study, the volume range of PAHG at 3 months follow-up was 0.217–1.365 cm³.
The amount of PAHG injected per treatment was 2 ml (= 2 cm³), but the median amount of bulking agent found by ultrasound immediately after the injection was only 1.2105 cm³
In a previous paper by Lose et al [10], the authors speculated that too much material injected per site might increase the risk of material leakage, either via the injection hole, or due to rupture of the covering mucosa. This might explain our findings. Because of the limited potential volume in the submucosal space, it is necessary to be aware about the amount of bulking agent injected. The optimal relationship between amount of injected material and cure rate has not been defined.
All the patients underwent imaging with 3DUS immediately after the surgery. Because of abundance of water in PAHG, all the deposits were seen as hypoechoic mass collections. In eleven patients (79%) four PAHG deposits were visualized and in three patients (21%) only three deposits. At 3 months follow-up, only 41 (77%) out of 53 deposits of bulking agent were left. Presence of fewer deposits than injected may represent loss of material through the urethra but might also be caused by confluence of deposits.
Mouritsen et al [9] found that PAHG deposits were still visible on vaginal ultrasound as hypoechoic collections even eight years post injection. In contrast to this previous study [9], only 24% of PAHG collections in our patients had hypo-echoic echogenicity at 3 months follow-up. Most bulking agent deposits had hyperechoic appearance.
Even though, we found a reduction in volume of PAHG 3 months after surgery, 78.6% of patients experienced improvement in their continence. Our results are comparable to reports in the literature on bulking agents [2, 10–12]. A subjective evaluation of continence status could overestimate the results. Sometimes even a minor objective leak decrease could be seen as a major continence improvement. We believe that PAHG has a place in a treatment of urinary incontinence with improvement of patients´ quality of life even with suboptimal treatment results.
The role of using 2D and/or 3DUS in the treatment of stress/mixed urinary incontinence with various urethral bulking agents as collagen, Coaptite, Macroplastique is well-described in previous studies [4, 13–18], but there is lack of studies using PAHG as bulking agent. Mouritsen et al [9] described volume and placement of the injected PAHG deposits at eight years follow-up. Unfortunately, the number and volume of the deposits around the urethra were not recorded with ultrasonography at the time of injection and hence a change in number and size of deposits over time could not be determined. To the best of our knowledge, our study is the first one to describe sonographic findings using urethral bulking agent PAHG immediately after treatment and at follow-up.
Limitations of the present study are a small cohort and a short follow-up. Using of 3DUS is an operator-dependent technology, which has the potential to skew results.
In this study no correlation between the clinical outcome and amount of bulking agent left at 3 months follow-up was found (Table 2). Our study population was too small to show a clinically significant difference and included a large percentage of patients with mixed urinary incontinence which makes conclusion on incontinence difficult. Furthermore, our study did not investigate the exact location of the bulking material.
We are not able to explain the echogenicity changes in some patients and not in others.
The strength of our study is that all procedures were performed at a high-volume specialty center of well-trained surgeons. The same validated questionnaires were used both pre- and postoperatively giving a more exact information about changes in urinary incontinence and no patients were lost to follow-up.
In conclusion, more than 1/3 of volume of injected PAHG and 23% of deposits could not be found by 3DUS at 3 months follow-up Only 24% of PAHG injections in our patients had hypo-echoic echogenicity at 3 months follow-up. Three-dimensional ultrasound examination can be easily applied in a clinical setting. Larger 3DUS studies with longer follow-up and focus on exact location of the PAHG injections are important future studies.