Ultrasonographic anatomy of perineal structures during pregnancy and immediately following obstetric injury

Abstract

To assess perineal anatomy using ultrasound before and immediately after delivery. Structures in the perineum were studied by real-time two-dimensional transvaginal and endoanal ultrasound imaging using a combined linear and semicircular (up to 200 degrees sector) probe. We examined 45 nulliparous pregnant women and 44 primiparae immediately after delivery (40 with anal sphincter tears and four without sphincter injury). In each case a single longitudinal image was later assessed by two observers in order to evaluate interobserver agreement. In pregnancy, the perineal membrane, puboperineal muscles, conjoined longitudinal muscle and central point were identified on real-time examination in 91%, 98%, 100% and 100% of cases, respectively. At offline evaluation of the longitudinal images obtained for each of the pregnant women, the percentage of cases in which each structure was identified by both observers ranged from 64% to 100%. In the women who were examined postpartum, all structures were identified by both observers in all four of the women without sphincter injury. In the women with sphincter tears, the perineal membrane, puboperineal muscles, conjoined longitudinal muscle and central point were found by ultrasound to be intact in 10%, 10%, 55% and 18%, respectively. The agreement between two observers regarding identification of intact structures in a single longitudinal image was good for perineal membrane (kappa index, 0.66), fair for puboperineal muscles (kappa index, 0.40), and poor for conjoined longitudinal muscle and central point (kappa index, 0.08 and 0.17, respectively). Ultrasonography might be helpful in the evaluation of perineal anatomy and extent of perineal tears. However, the relatively poor agreement between the two observers evaluating single linear transvaginal images implies that both transverse and longitudinal projections are necessary to obtain relevant information. Further studies are needed regarding the importance of specific sonographically identified structures and their role in pelvic floor dysfunction after delivery.