Analysis of Minimal Levator Ani Hiatus Area Based on MRI in Women without Pelvic Floor Dysfunction at Different Age Groups

Abstract Purpose : To investigate the association of minimal levator ani hiatus area with age in women without pelvic floor dysfunction. Methods : 552 female subjects aged one year ~90 years without pelvic floor dysfunction, divided into four groups (Group A, ≤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 dimension (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 dimension (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 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. Results : Female age was positively correlated with minimal levator ani hiatus area ( r = 0.29; p < 0.001). The minimal levator ani hiatus areas of 552 subjects were: 13.74±3.48 cm 2 in Group A, 15.52±2.21 cm 2 in Group B, 16.03±2.16 cm 2 in Group C and 16.40±2.10 cm 2 in Group D. ANOVA showed significant statistical differences among four age groups (F=23.99, p ＜0.0001). Significant differences in minimal levator ani hiatus areas were found between Group A and Group B ( p = 0.0012), Group A and Group C ( p < 0.0001), Group A and Group D ( p < 0.0001), and Group B and Group D ( p < 0.0001). There was no statistical difference in minimal levator ani hiatus areas measured on AxB and AxPRM images in 39 female volunteers ( p = 0.1000). Conclusions : Based on a large sample, this study summarized the minimum levator ani hiatus area of women 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 women of different age groups.