RACIAL DIFFERENCES IN PELVIC GEOMETRY AMONG ASYMPTOMATIC NULLIPARAS AS SEEN ON THREE-DIMENSIONAL MAGNETIC RESONANCE IMAGES

L. Hoyte, J.Thomas, R.T. Foster, M. Jakab, A.C. Weidner

Loyola University Medical Center, Maywood, IL

OBJECTIVE:  To assess morphology of the bony and soft tissue pelvic organs in nulliparous African-American and Caucasian women using three-dimensional magnetic resonance imaging.
MATERIALS AND METHODS:  Supine MR images at rest were obtained in 22 nulliparous women:  12 were African-American (AA) and 10 were Caucasian (CA).  All subjects had Stage 0 or 1 pelvic support by the POPQ system and all denied symptoms of pelvic floor dysfunction.   High resolution T2 weighted axial pelvic MR images were obtained, from which 3D reconstructions were made. The reconstructed 3D models were used to measure predefined bony and soft tissue pelvic parameters, and these were compared between the two groups.  The bony parameters included intertuberous and interspinous distance, pubic arch angle, and the pubo-coccygeal line. Soft tissue parameters included levator ani shape, volume, and anterior puborectalis attachment, as well as bladder neck position.  Mann-Whitney testing was used to compare the measures between groups. The SPSS statistical package was used, and significance was taken at p <0.05.
RESULTS:  Subject groups did not differ by age (AA: 29.3 yrs [23.2-43.9] vs CA: 24.9yrs [19.6-34.7]) or body mass index (AA: 26.5kg/m2 [21-47.7] vs CA: 24.2kg/m2 [23-34]).  Of the bony pelvic measures, only the pubic arch angle was seen to be significantly different between the groups. Among the African American (AA) nullips,  pubic arch angle (mean, [range]) was 99 [64-125] degrees, compared to 86 [78-98] degrees among the Caucasians(p=.007). Soft tissue parameters showing significant differences were bladder neck to symphysis (AA mean=19.0,range [11.5-22.0] vs CA mean=16.5 range[11.6-21.0] mm, p=0.048 ), the angle of the urethra to the mid symphyseal line (mean, range: AA 49.2 [40.6-62.9] vs CA 56.4[43.7-71.7] degrees, p=0.035 ),  levator ani volume (AA 26.8[19.0-33.9] vs CA 19.8 [13.5-29.1] cc, p=.002), and the levator symphysis gap on the left (AA  18.2,[14.6-22.4] vs CA 22.4 [18.6-30.13] mm, p=.003) and on the right(AA 18.8 [11.3-21.9] vs CA 22.6 [18.6-30.5] mm, p=.048).
CONCLUSIONS:  Significant differences in pelvic soft tissue geometry is seen between African American nulliparas when compared to age matched Caucasian nulliparas. Increased pelvic muscle bulk is seen among the African American nulliparas. The pubic arch angle is slightly but significantly larger in our group of African American nulliparas, compared to the Caucasians. Further studies are needed to evaluate the clinical significance of these differences and their impact on pelvic floor dysfunction risk factors. (Support: NIH R01 HD38661, NIH-P01 CA67165-06)

Key Words:  magnetic resonance, levator ani, pelvis, race, 3D reconstruction

Disclosure - Speakers Bureau: L. Hoyte, Odyssey/Indevus Pharm; Advisory Board: L. Hoyte, Volugraphics Inc.