50: Pelvic MRI measurements of estimated levator ani subtended volume and correlation to aging levator ani muscle tissue

Abstract

The levator ani muscle plays an important role in pelvic support. Studies have confirmed levator ani muscle defects as a risk factor for developing pelvic organ prolapse. Estimated levator ani subtended volume (eLASV) is an objective 3D measurement of levator ani muscle integrity and has been demonstrated to be correlated with worsening pelvic organ prolapse though anatomical changes of the muscle. The aim of this study was to assess the relationship between eLASV calculated from pelvic MRIs and age of the patient. Our hypothesis is that increasing age will be directly related to the increasing values of eLASV measurements (i.e., the older the patient, the larger the eLASV value, representing a decrease in the muscle integrity and strength). We conducted an IRB approved retrospective cohort study. Medical records of women who underwent a pelvic MRI from January 1, 2010 to December 31, 2011 were reviewed. Standard protocol pelvic MRI measurements, including the pubococcygeal line, H-line, and M-line were collected along with the calculated width of the levator ani hiatus. The eLASV (eLASV= -72.838+0.598H-line+1.217M-line+1.136WLH) was then calculated for each patient and a pre-determined optimal cutoff value, based on a previous publication [1], was used to classify patients as <38.5 or ≥38.5. Patient age was categorized as <60 and ≥60 based on the mean age of the population. Differences in age among eLASV classification were assessed using the Wilcoxon-Mann-Whitney (continuous age) and chi-square test (age group). Spearman’s correlation analysis was used to explore the relationship between age and eLASV. Logistic regression was used to obtain crude odds ratio (OR) to determine the association between age and eLASV. Sixty-six women underwent a pelvic MRI during the study period. Mean age was 59.2 ±11.3, mean BMI was 27.5±4.6, median parity of 2 range (0-5), and median POP stage of 3 range (1-4). As seen in table 1, patients with eLASV > 38.5 were more likely to be older [65.0 (37, 83) vs 49.5 (28, 72) p=0.001]. We observed a moderate correlation between age and eLASV (rs=0.52, p<0.001). Lastly, patients older than 60 years of age were 6.6 times more likely to have an eLASV1 > 38.5 compared to patients <60 (OR: 6.55, 95% CI: 2.19 – 19.56). Levator ani muscle integrity as measured by pelvic MRI eLASV calculation appears to be correlated to the age of women. This study supports our hypothesis that eLASV represents an objective measurement of the levator ani muscle integrity of a woman. Increasing age in women resulting in a decrease in strength of levator ani muscles appears to be directly related to the objective measurement of eLASV.