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

Purpose: Few studies are available on imaging the urethral sphincter. We pe rformed transvaginal ultrasonography to examine the muscle in continent and incontinent women. Materials and Methods: 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 include d urethral hypermobility (22) and intrinsic sphincter deficiency (33). Cada ver specimens were also examined to confirm the anatomy of ultrasound image s. Results: Transvaginal ultrasonography showed the urethra as a round structu re 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 rhabdosp hincter most reliably at the lateral aspects. Thus, its thickness was measu red at the 9 o'clock position of the mid urethra. Mean thickness plus or mi nus standard error of mean was significantly decreased in stress incontinen ce compared with continence and urge incontinence (2.14 +/- 0.04, 2.78 +/- 0.08 and 2.87 +/- 0.11 mm., respectively, p <0.001), while in intrinsic sph incter deficiency it was thinner than in hypermobility (2.00 +/- 0.05 versu s 2.35 +/- 0.06 mm., p <0.01). There was no difference in central zone thic kness according to continence status. Conclusions: Urethral structures may be visualized by transvaginal ultrason ography. The rhabdosphincter image was thinner in stress incontinence, espe cially in intrinsic sphincter deficiency. Transvaginal ultrasonography may be a useful clinical test for examining the morphology of the urethral sphi ncter muscle in women.