Transvaginal ultrasound of urethral sphincter at the mid urethra in continent and incontinent women

Few studies are available on imaging the urethral sphincter. We performed transvaginal ultrasonography to examine the muscle in continent and incontinent women.Transvaginal ultrasonography was performed using a 7.5 MHz. transrectal probe in 19 continent and 69 incontinent supine women. Incontinent cases were classified as urge (14) and stress (55), and included urethral hypermobility (22) and intrinsic sphincter deficiency (33). Cadaver specimens were also examined to confirm the anatomy of ultrasound images.Transvaginal ultrasonography showed the urethra as a round structure consisting of a relatively high echogenic central zone and a relatively low echogenic peripheral zone. Matching ultrasound images with the anatomy of cadaver specimens indicated that the peripheral zone represents rhabdosphincter most reliably at the lateral aspects. Thus, its thickness was measured at the 9 o'clock position of the mid urethra. Mean thickness plus or minus standard error of mean was significantly decreased in stress incontinence compared with continence and urge incontinence (2.14 +/- 0.04, 2.78 +/- 0.08 and 2.87 +/- 0.11 mm., respectively, p0. 001), while in intrinsic sphincter deficiency it was thinner than in hypermobility (2.00 +/- 0.05 versus 2.35 +/- 0.06 mm., p0.01). There was no difference in central zone thickness according to continence status.Urethral structures may be visualized by transvaginal ultrasonography. The rhabdosphincter image was thinner in stress incontinence, especially in intrinsic sphincter deficiency. Transvaginal ultrasonography may be a useful clinical test for examining the morphology of the urethral sphincter muscle in women.