General Obstetrics and Gynecology: Gynecology
A structured system to evaluate urethral support anatomy in magnetic resonance images,☆☆

Presented at the American Urogynecologic Society Twenty-first Annual Scientific Meeting, Hilton Head, South Carolina, October 26-28, 2000.
https://doi.org/10.1067/mob.2001.116368Get rights and content

Abstract

Objective: To develop a systematic method for analyzing the normal magnetic resonance imaging location and appearance of structural features involved in urethral support. Study Design: Multiplanar proton density magnetic resonance images of 50 nulliparous women were made at 0.5-cm intervals. The arcuate pubic ligament was the chosen reference point in all views. Structural features were located by identification of the magnetic resonance images in which they appeared. The presence or absence of urethral support structures in each scan level relative to the arcuate pubic ligament was evaluated and recorded as a graphic display. Support structures examined were the arcus tendineus fasciae pelvis, the perineal membrane, the pubococcygeal levator ani muscle and its vaginal and bony attachments, and the pubovesical muscle. Structural definitions were developed on the basis of established periurethral anatomy. Two examiners independently assessed 10 scans for interobserver concordance. This system was used in nulliparous women to quantify the location of magnetic resonance visible structures. Results: Because all levels were 0.5 cm apart, slice identification represented the distance above the arcuate pubic ligament (eg, 2 images above the arcuate pubic ligament or 1.0 cm). Interobserver concordance was 88% in identification of structure location. In the axial plane, specific structural features and relationships were localized. The frequency at which a specific structure was observed at a specific image level in all women was depicted as a gray density within the graphic display. These frequencies indicated where we would expect each structure to be located in healthy women. Relationships between structures and their attachments became apparent. Consideration of expected structural locations proven by nulliparous scans will enable us to quantitatively define abnormal structures in parous women. Conclusions: This systematic magnetic resonance evaluation allows, for the first time, quantification of the normal anatomic location of urethral support structures. It can be used to help identify the difference between structural abnormalities and normal variation in parous women. (Am J Obstet Gynecol 2001;185:44-50.)

Section snippets

Methods

Fifty nulliparous women were recruited for an Institutional Review Board–approved case-control study that concerned vaginal delivery and stress urinary incontinence. After the women gave informed consent, multiplanar 2-dimensional fast spin (echo time, 15 ms; repetition time, 4000 ms) proton density MR images of all pelves were obtained by use of a 1.5-tesla superconducting magnet (Signa; General Electric Medical Systems, Milwaukee, Wis) with version 5.4 software. The slice thickness was 4 mm

Results

The demographic information for the nulliparous women is shown in Table I.

. Demographic characteristics

CharacteristicNulliparous (n = 50)
Age (y, mean ± SD)29.340 ± 5.236
Body mass index (kg/m2, mean ± SD)25.097 ± 5.868
Race
 White35 (70%)
 Black12 (24%)
 Hispanic1 (2%)
 Asian1 (2%)
 Other1 (2%)
An example of a series of 12 consecutive axial images taken from a typical nulliparous woman is shown in Fig 1. Note the APL reference point in the image labeled A. Specific bony landmarks, periurethral support

Comment

This study establishes a method to systematically evaluate MR images of pelvic support structures. In fact, this approach may be used to organize and collect observations for any multilevel radiologic imaging study. The advantage of MR imaging is its ability to vividly reveal soft tissue structures without the use of contrast dyes or invasive probes. We found that proton density MR images provided the best resolution of pelvic support structures. We were able to achieve sufficient structural

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Supported by grant RO1 DK51405-01A1 from the National Institute of Diabetes and Digestive and Kidney Diseases.

☆☆

Reprint requests: Queena Chou, MD, Department of Obstetrics and Gynecology, St Joseph’s Health Care London, 268 Grosvenor St, Room E361, London, Ontario, Canada N6A 4L6.

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