The Location and Distribution of Transurethral Bulking Agent: 3-Dimensional Ultrasound Study

Objectives To use 3-dimensional endovaginal ultrasound to describe the location and distribution of bulking agent after an uncomplicated transurethral injection. Methods Endovaginal ultrasound was performed in 24 treatment-naive patients immediately after bulking agent was injected. The distance between the center of the hyperechoic density of bulking agent and the urethrovesical junction (UVJ) was measured in the sagittal and axial views. This was calculated in percentile length of urethra. Also, the pattern of tracking of bulking agent was assessed if it is presented. Results After the 2 subjects were excluded because of the poor quality of images, 22 patients were included in this study. Eighteen (82%) subjects showed 2 sites of bulking agents, and mostly, they were located around 3- and 9-o'clock positions. The average distance of bulking agent from left UVJ was at 16.9% of the length of the urethra (6.2 mm; range, 0.5-17 mm) and at 25.5% of the length of the urethra (8.9 mm; range, 0-24.8 mm) in the right side. The average length of urethra was 36.7 mm. Eleven of the 22 subjects (50%) had both sides within upper one third of urethra. The difference in distance between the 2 sides was less than 10 mm in 12 of 22 patients (54%). Nine of the 22 patients (41%) had a significant spread of bulking agent mostly either into the bladder neck or toward the distal urethra. Conclusions Although the bulking agent is most often found at 3- and 9-o'clock positions as intended, the distance from the UVJ is highly variable after an uncomplicated office-based transurethral injection. The bulking material does not form the characteristic spheres in 41% of cases and tracks toward the bladder neck or the distal urethra.