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Measuring the levator hiatus with axial MRI sequences: Adjusting the angle of acquisition

Authors

  • W. Thomas Gregory M.D.,

    Corresponding author
    1. Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Portland, Oregon
    • Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, 3181 SW Sam Jackson Park Rd, Mail Code L466, Portland, OR 97239.
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  • Rahel Nardos,

    1. Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Portland, Oregon
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  • Teresa Worstell,

    1. Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Portland, Oregon
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  • Amy Thurmond

    1. Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Portland, Oregon
    2. Department of Radiology, EPIC Imaging West, Beaverton, Oregon
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  • Conflicts of interest: none

  • Heinz Koelbl led the review process.

Abstract

Aims

We aimed to compare MRI measurements of the female levator hiatus and the most caudal “levator ani” muscles between image slices in a plane axial to the body (AxB) and an axial plane parallel to the direction of the puborectalis muscle (AxPRM).

Methods

We performed high-resolution, T2-weighted axial magnetic resonance imaging (in two different planes) on 20 sequentially recruited asymptomatic nulliparous women. Levator hiatus measurements were compared between the two planes.

Results

The mean tilt angle of the AxPRM slices relative to the AxB slices was 18.9° (SD 8.5) and the area of the levator hiatus was 10% greater (P = 0.04) in the AxPRM plane.

Conclusions

By rotating the acquisition plane to be parallel to the puborectalis muscle (sometimes called the plane of minimal hiatal dimensions), some of the measurements of the distal and medial pelvic floor muscles (and the hiatus defined by them) are altered. This issue is important because both MRI and 3D ultrasound are increasingly being used to evaluate the pelvic floor hiatus, and its relationship to childbirth injury and pelvic floor disorders. To make meaningful comparisons, it is important that both modalities are measuring the same thing. Neurourol. Urodynam. 30:113–116, 2011. © 2010 Wiley-Liss, Inc.

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