Analysis of minimal levator ani hiatus area based on MRI in female adults without pelvic floor dysfunction at different age groups

To investigate the association of minimal levator ani hiatus area with age in female adults without pelvic floor dysfunction.

532 female subjects aged 18 ~ 90 years without pelvic floor dysfunction, divided into four groups (Group A, 18 ~ 29 years old; Group B, 30 ~ 39 years old; Group C, 40 ~ 49 years old; Group D, ≥ 50 years old) based on age, underwent traditional pelvic two-dimensional (2D) T2-weighted imaging (T2WI) axial to the body (AxB) for measuring the minimal levator ani hiatus area. 39 female volunteers were re-recruited to undergo both traditional pelvic 2D T2WI AxB and three-dimensional (3D) T2WI. An axial plane parallel to the direction of the puborectalis muscle (AxPRM) was acquired based on 3D T2WI. The difference of levator ani hiatus area measured on AxB and AxPRM images in 39 female volunteers was compared by one-sample t test, to verify if minimal levator ani hiatus area can be acquired on the traditional pelvic 2D T2WI AxB images. Spearman analysis evaluated the association of minimal levator ani hiatus area with age and the rank-sum test analyzed the area differences among four age groups.

Female age was positively correlated with minimal levator ani hiatus area (r = 0.23; p < 0.001). The minimal levator ani hiatus areas of 532 subjects were: 15.17 ± 1.77 cm² in Group A, 15.52 ± 2.21 cm² in Group B, 16.03 ± 2.16 cm² in Group C, and 16.40 ± 2.10 cm² in Group D. ANOVA showed significant statistical differences among four age groups (F = 7.519, p < 0.0001). Significant differences in minimal levator ani hiatus areas were found between Group A and Group C (p = 0.0491), Group A and Group D (p = 0.0007), and Group B and Group D (p < 0.001). There was no statistical difference in minimal levator ani hiatus areas measured on AxB and AxPRM images in 39 female volunteers (p = 0.1000). There were no statistical difference in minimal levator ani hiatus areas between nulliparous and multiparous group for each age group (all p > 0.05).

Based on a large sample, this study summarized the minimum levator ani hiatus area of female adults without pelvic floor dysfunction in different age groups. We found significant differences among different age groups. In addition, a positive correlation was found between age and the minimum levator ani hiatus area. These findings can provide reference criteria for diagnosing pelvic organ prolapse in female adults of different age groups.