Perineal structural changes on 3-dimensional endovaginal ultrasound 6 months after difficult vaginal birth: the Hourglass-Band pattern and how it relates to levator ani avulsion and hiatus size.

Abstract

Current evidence indicates that pelvic organ prolapse development after childbirth is strongly associated with an enlarged hiatus. However, few childbirth-related injuries beyond anal sphincter lacerations and levator ani avulsion-which explain less than a quarter of hiatal enlargement-have been investigated. Other types of injuries that lead to an enlarged hiatus and contribute to prolapse development remain incompletely explored. The perineal complex components (perineal membrane, perineal body, and levator ani) are responsible for hiatal closure and form a distinct anatomical and functional unit. Yet how and whether this complex is injured during childbirth and how such injuries can be identified through imaging has not been well characterized in the literature. We sought to evaluate the perineal complex components using 3-dimensional endovaginal ultrasound at 6 months postpartum and how potential defect patterns are influenced by mode of delivery. Additionally, we explored how potential defect patterns are associated with clinical and obstetric data. This was a secondary analysis of data from a prospective longitudinal study of postpartum women at high risk for pelvic floor injury. We used 6-month 3-dimensional endovaginal ultrasound images and data to evaluate the 3 perineal complex components and developed and applied a scoring system to assess for potential imaging abnormalities. A total of 126 women were included in the present study. In women with no visible anatomic abnormality, there was a convergence of tissue to the midline at the perineal body level that was not present in other scans. This configuration was divided into 2 features: an hourglass appearance and a visible transverse band, which together we termed the Hourglass-Band pattern. In women with a vaginal delivery (n=94), the 2 features were 2.4 and 4.1 times more likely to be absent, respectively. The Hourglass-Band pattern was altered in 45% of vaginal deliveries, indicating level III imaging abnormalities in nearly half the cohort and highlighting the prevalence of childbirth-related changes among high-risk women. In the cesarean delivery control group (n=32), an altered Hourglass-Band pattern was seen in 16% of subjects, suggesting the possibility of anatomical variation or differences in sonographic tissue characteristics. The altered Hourglass-Band pattern is an imaging abnormality that is strongly associated with difficult vaginal birth, distinct from levator ani avulsion and anal sphincter laceration, and potentially repairable. If confirmed as a childbirth-related injury, studying Hourglass-Band alterations could enhance our understanding of alternative injury mechanisms and inform pelvic floor injury prevention and recovery strategies postpartum.