Reference line lengthening on resting-state magnetic resonance imaging in patients with pelvic organ prolapse seeking surgical treatment

Injury to and laxity of the pelvic floor muscles are highly important factors in the etiology of pelvic organ prolapse. When women with pelvic organ prolapse perform the Valsalva maneuver, progressive descent and widening of the levator ani muscle are observed on dynamic magnetic resonance images. However, physical examination of such women often reveals pelvic floor laxity, even in a relaxed state. Therefore, we aimed to verify the hypothesis that sagging of the pelvic floor can be detected on resting-state magnetic resonance images in the supine position.

We retrospectively evaluated resting-state magnetic resonance imaging findings in women with (n = 193; all underwent surgical treatment) and without (controls; n = 193) pelvic organ prolapse who had at least one prior vaginal delivery. We compared the lengths of the pubococcygeal line, H-line, and M-line between the groups.

The median lengths (interquartile ranges) for the prolapse and control groups were 98.3 (91.9-104.0) and 95.1 (90.3-101.4) mm (p = 0.0011), respectively, for the pubococcygeal line; 61.5 (56.0-67.9) and 51.1 (47.2-55.6) mm (p < 0.0001), respectively, for the H-line; and 24.6 (20.4-29.0) and 8.6 (3.9-13.0) mm (p < 0.0001), respectively, for the M-line. Similarly, in the multiple regression analysis adjusted for age, height, body mass index, a history of operative vaginal delivery, and a history of hysterectomy, the pubococcygeal line, H-line, and M-line were significantly longer in the prolapse group.

In women with pelvic organ prolapse, the H-line and M-line are significantly longer on resting-state magnetic resonance images, allowing for the detection of pelvic floor relaxation.