Three-dimension Imaging Study On Anatomy And Function Of The Levator Ani With Pelvic Floor Dysfunction

【Objective】This study was designed:1)to observe the appearance of levator ani subdivisions using magnetic resonance based three dimensional models;2)quantification of levator defect using three dimensional ultrasound and magnetic resonance based models;3)to correlate the levator defect with the degree of pelvic organ prolapse;4)to compare the agreement between the two imaging methods.【Methods】Part one:MRI-based three dimensional reconstruction of levator ani in nulliparous women and women with pelvic organ prolapse High resolution supine 3D MRI at rest were performed on 10 nulliparous women and 66 women with pelvic organ prolapse. Segmentation and 3D reconstruction of 4 pelvic structures - the symphysis, levator ani, and sacrococcygeal bone were performed on each subject. Characteristic features of each Terminologia Anatomica listed levator ani component were determined for eachscan plane.By evaluating the 3D reconstruction,A levator avulsion was diagnosed if a "disconnection" of the muscle from the inner surface of pubic bone. we measured the levator symphysis gap (LSG),the puborectalis width (PAW),the levator hiatus height(LHH)and the levator hiatus width(LHW) on 3D models. A Cochran-Armitage test was employed to detect the trend between levator defect and severity of POP,a linear regression test was applied to assess the relationship between ordinal stages of POP and measurements.Part two: Levator avulsion using a tomographic ultrasound and magnetic resonance based modelsSixty-nine Chinese women with pelvic organ prolapse were assessed prospectively, using 3D ultrasound and MRI. Levator-urethra gap (LUG), levator-symphasis gap (LSG) and puborectalis attachment width (PAW) were measured offline using state-of-the-art software. Inter-observer variability and agreement between the two methods were determined. Part three: The effect of levator avulsion on hiatus dimension and function126 Patients underwent an interview, clinical examination, and 3-/4-dimensional pelvic floor ultrasound. All analysis was performed offline using proprietary software. Hiatal dimensions and strain were measured. A Cochran-Armitage test was employed to detect the trend between levator defect and severity of POP,analysis of variance was used to compare healthy patients with those showing unilateral and bilateral avulsion.【Results】Part one:MRI-based three dimensional reconstruction of levator ani in nulliparous women and women with pelvic organ prolapseThe axial plane provides a clear view of the pubovisceral muscle and its subdivisions.MRI-based three dimensional models can give a topographical overview of levator ani.The most common type of levator avulsion is detachment from inner surface of pubic bone. The incidence of levator avulsion was positive correlated with the degree of pelvic organ prolapse in anterior and middle compartments but not in posterior compartment.The dimensions of levator hiatus were positive correlated with the severity of POP in anterior and middle compartments but not in posterior compartment. Part two: Levator avulsion using a tomographic ultrasound and magnetic resonance based modelsInter-observer repeatability was moderate to excellent for all parameters measured with both methods and agreement between methods in diagnosing levator avulsion. LUG and LSG measurements were significantly higher in women with a levator avulsion.Diagnosing complete levator avulsion, receiver–operating characteristics analysis suggested a cut-off of 23.65mm for LUG and 28.7mm for LSG. Part three: The effect of levator avulsion on hiatus dimension and functionThe proportion of levator avulsion was positive correlated with the degree of pelvic organ prolapse in anterior and middle compartments but not in posterior compartment.The dimensions of levator hiatus were positive correlated with the severity of POP in anterior and middle compartments but not in posterior compartment.Avulsion increased muscle distensibility on Valsalva and reduced muscle shortening on pelvic floor muscle contraction.【Conclusion】1. The subdivisions of the levator ani muscle are visible in MRI-based 3D models, each with distinct morphology and characteristic features. 3D models can give a topographical overview of levator ani and show the details of levator defect.Delivery-related levator trauma can cause pelvic organ prolapse in anterior and middle compartment.2. Levator avulsion can be reliably diagnosed by tomographic ultrasound and MRI evaluation and linear measures like LSG and LUG can be proxy measurements for avulsion. 3. Avulsion increased muscle distensibility and hiatus dimension and reduced muscle shortening on pelvic floor muscle contraction.