Technique development and measurement of cross-sectional area of the pubovisceral muscle on MRI scans of living women
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Introduction and hypothesis
Measurements of the anatomic cross-sectional area (CSA) of the pubovisceral muscle (PVM) in women are confounded by the difficulty of separating the muscle from the adjacent puborectal (PRM) and iliococcygeal (ICM) muscles when visualized in a plane orthogonal to the fiber direction. We tested the hypothesis that it might be possible to measure the PVM CSA within a defined region of interest based on magnetic resonance images (MRI).
MRI scans of 11 women with unilateral PVM tears and seven primiparous women with intact muscles following elective C-section were used to identify the PVM injury zone defined by the mean location of its boundaries with the adjacent intact PRM and ICM from existing anatomic reference points using 3D Slicer and ImageJ software. Then, from the 15 or more 2-mm transverse slices available, the slice with the maximum anatomic CSA of the left and right PVM was found in 24 primiparous women with bilaterally intact muscles who had delivered via C-section.
Mean [± standard deviation (SD)] of the maximum left or right PVM cross-section areas for the 24 women, measured by two different raters, was 1.25 ± 0.29 cm2 (range 0.75–1.86). The 5th, 50th, and 95th percentile values were 0.77, 1.23, and 1.80 cm2, respectively. Inter- and intrarater measurement repeatability intraclass correlation coefficients exceeded 0.89 and 0.90, respectively.
It is possible to use MRI to identify the volume of interest with the maximum anatomic cross section of the PVM belly while minimizing the inadvertent inclusion of adjacent PRM or ICM in that measurement.
KeywordsCross-sectional area MRI Pubovisceral muscle
We thank Bing Xie, MD, for her support in the data analysis portion of this paper. We also thank Janis M. Miller, PhD, the principal investigator for the EMRLD project, for generously allowing us to use those MRI scans. Finally, we thank the women who were willing to be tested for these studies.
We are grateful for the Public Health Service and the Office for Research on Women and Gender Grants #P50 HD044406-07 and HD R01 38665 (JAAM & JOLD). MM was supported by the Fulbright Program for her masters dissertation research in Ann Arbor while a graduate student at the University of Porto, Portugal.
Compliance with ethical standards
Conflict of interest
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