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

Analysis of minimal levator ani hiatus area based on MRI in female adults without pelvic floor dysfunction at different age groups

PURPOSE

To investigate the association of minimal levator ani hiatus area with age in female adults without pelvic floor dysfunction.

METHODS

532 female subjects aged 18 ~ 90 years without pelvic floor dysfunction, divided into four groups (Group A, 18 ~ 29 years old; Group B, 30 ~ 39 years old; Group C, 40 ~ 49 years old; Group D, ≥ 50 years old) based on age, underwent traditional pelvic two-dimensional (2D) T2-weighted imaging (T2WI) axial to the body (AxB) for measuring the minimal levator ani hiatus area. 39 female volunteers were re-recruited to undergo both traditional pelvic 2D T2WI AxB and three-dimensional (3D) T2WI. An axial plane parallel to the direction of the puborectalis muscle (AxPRM) was acquired based on 3D T2WI. The difference of levator ani hiatus area measured on AxB and AxPRM images in 39 female volunteers was compared by one-sample t test, to verify if minimal levator ani hiatus area can be acquired on the traditional pelvic 2D T2WI AxB images. Spearman analysis evaluated the association of minimal levator ani hiatus area with age and the rank-sum test analyzed the area differences among four age groups.

RESULTS

Female age was positively correlated with minimal levator ani hiatus area (r = 0.23; p < 0.001). The minimal levator ani hiatus areas of 532 subjects were: 15.17 ± 1.77 cm2 in Group A, 15.52 ± 2.21 cm2 in Group B, 16.03 ± 2.16 cm2 in Group C, and 16.40 ± 2.10 cm2 in Group D. ANOVA showed significant statistical differences among four age groups (F = 7.519, p < 0.0001). Significant differences in minimal levator ani hiatus areas were found between Group A and Group C (p = 0.0491), Group A and Group D (p = 0.0007), and Group B and Group D (p < 0.001). There was no statistical difference in minimal levator ani hiatus areas measured on AxB and AxPRM images in 39 female volunteers (p = 0.1000). There were no statistical difference in minimal levator ani hiatus areas between nulliparous and multiparous group for each age group (all p > 0.05).

CONCLUSIONS

Based on a large sample, this study summarized the minimum levator ani hiatus area of female adults without pelvic floor dysfunction in different age groups. We found significant differences among different age groups. In addition, a positive correlation was found between age and the minimum levator ani hiatus area. These findings can provide reference criteria for diagnosing pelvic organ prolapse in female adults of different age groups.

Levator-Urethra Gap: Normative Data in a Nonpregnant Nulliparous Population

OBJECTIVE

This study aimed to establish a normative range of the levator-urethra gap (LUG) measurement in nonpregnant, nulliparous women to be used as a standard against which assessments of injury or avulsion of the levator ani could be made.

METHODS

Nulliparous women in the Pacific Northwest who were planning pregnancy within the ensuing 12 months underwent high-resolution magnetic resonance imaging (MRI) and 3-dimensional transperineal ultrasonography. In the plane of minimal hiatal dimensions, the LUG was measured on both the right and left sides for 3 contiguous image slices.

RESULTS

One hundred thirty-five participants underwent examinations, of which 134 had evaluable MRIs and 70 had evaluable ultrasounds. Mean (SD) age was 30.8 (4.0) years, and mean (SD) body mass index was 25.9 (6.4). The majority of the participants self-identified as White (80%) and non-Hispanic (89%). The 99th percentile was no greater than 2.39 cm on any slice for either MRI or US-based measurements. In the MRI set, the lowest LUG values at which all 3 measurements on a side were found to have exceeded a putative threshold value (for injury) were 2.1 cm for the right side and 2.05 cm for the left side. The corresponding LUG values in the ultrasound set were 2.2 cm on the right and 2.25 cm on the left.

CONCLUSIONS

The LUG threshold in 3 successive slices in the minimal hiatal dimension suggestive of levator ani injury could be as low as 2.1 cm when using MRI and 2.25 cm when using ultrasound in a similar population.

Injury-associated levator ani muscle and anal sphincter ooedema following vaginal birth: a secondary analysis of the EMRLD study

OBJECTIVE

To determine whether all three components of the levator ani muscle (pubovisceral [= pubococcygeal], puborectal and iliococcygeal) and the external anal sphincter are equally affected by oedema associated with muscle injury after vaginal birth.

DESIGN

Observational cross-sectional study.

SETTING

Michigan Medicine, University of Michigan.

POPULATION

Primiparous women classified as high risk for levator ani muscle injury during childbirth.

METHOD

MRI scans obtained 6-8 weeks postpartum were analysed. Muscle oedema was assessed on axial and coronal fluid-sensitive magnetic resonance (MRI) scans. Presence of oedema was separately determined in each levator ani muscle component and in the external anal sphincter for all subjects. Descriptive statistics and correlation with obstetric variables were obtained.

MAIN OUTCOME MEASURES

Oedema score on fluid-sensitive MRI scans.

RESULTS

Of the 78 women included in this cohort, 51.3% (n = 40/78) showed muscle oedema in the pubovisceral (one bilateral avulsion excluded), 5.1% (n = 4/78) in the puborectal and 5.1% (n = 4/78) in the iliococcygeal muscle. No subject showed definite oedema on external anal sphincter. Incidence of oedema on the pubovisceral muscle was seven times higher than on any of the other analysed muscles (all paired comparisons, P < 0.001).

CONCLUSIONS

Even in the absence of muscle tearing, the pubovisceral muscle shows by far the highest incidence of injury, establishing that levator components are not equally affected by childbirth. External anal sphincter did not show oedema-even in women with sphincter laceration- suggesting a different injury mechanism. Developing a databased map of injured areas helps understand injury mechanisms that can guide us in honing research on treatment and prevention.

TWEETABLE ABSTRACT

Injury-associated levator ani muscle and anal sphincter oedema mapping on MRI reveals vulnerable muscle components after childbirth.

Changes in Morphology of the Urethral Rhabdosphincter Postpartum

OBJECTIVE

The aim of the study was to determine the effect of pregnancy on urethral rhabdosphincter cross-sectional area (CSA) and any association of CSA to urinary symptoms.

METHODS

Nulliparous women planning pregnancy (N = 135) underwent standardized evaluations (symptom and quality of life [QOL] questionnaires, magnetic resonance imaging, ultrasonography, and neurophysiologic testing) between January 2008 and December 2013 (V1). The participants who became pregnant and gave birth underwent the same evaluations at 6 weeks (V2) and 6 months postpartum (V3). Participants who had magnetic resonance imaging data from both V1 and V3 were selected. We measured urethral rhabdosphincter CSA from high-resolution axial MRIs in a masked fashion. The mean CSA for each participant was calculated. The change from V1 to V3 was assessed.

RESULTS

Sixty-eight women were evaluated. There was a significant decrease of 0.05 cm2 (interquartile range, -0.03 to 0.16 cm2; P = 0.002) in the median sphincter CSA between V1 and V3. There was a significant increase in the median Urinary Distress Inventory (UDI) subscore of the Pelvic Floor Distress Inventory (PFDI) from V1 to V3 (median increase of 0 [IQR, 0 to 8.3]; P = 0.033), but this was not significantly correlated with the change in the urethral CSA (Spearman correlation, 0.199; P = 0.107). Increasing fetal weight was correlated with a decrease in CSA postpartum after vaginal birth (Spearman correlation, -0.340; P = 0.017).

CONCLUSIONS

There is a decrease in urethral rhabdosphincter CSA with worsening Urinary Distress Inventory scores from prepregnancy to postpartum, but these two do not correlate in this cohort with low symptom levels. Among women who give birth vaginally, decrease in rhabdosphincter CSA is correlated with increasing fetal weight, perhaps with ramifications to be seen later in life.

Comparing 3-Dimensional Ultrasound to 3-Dimensional Magnetic Resonance Imaging in the Detection of Levator Ani Defects

OBJECTIVE

The aim of this study was to compare the detection of levator ani defects (LAD) between 3-dimensional (3D) ultrasound (US) and 3D magnetic resonance imaging (MRI).

METHODS

This is a secondary analysis of the Pelvic Floor Nerve Injury Following Childbirth Study. Nulliparous women underwent a standardized protocol of pelvic floor evaluations between January 2008 and December 2013, prior to pregnancy (V1) and at 2 points postpartum: 6 weeks (V2) and 6 months (V3). Those women who underwent a high-resolution 3D MRI pelvic floor sequence were selected. Comparisons were made to concomitantly acquired 3D perineal US. Eight tomographic slices were examined in the axial plane, each side independently scored with 0 (no defect) or 1 (defect). A similar tomographic approach was applied to the MRI. For both MRI and US, the right and left sides were each scored. A total score of 0 to 8 was given to each side. A dichotomous variable "complete LAD" was defined. Cohen κ was used as a measurement of agreement of complete LAD between MRI and US. Kendall τ b was used to correlate total scores.

RESULTS

On the right side, 80 (90%) of 89 pairs were in agreement (concordant in the diagnosis or not of a "defect"). On the left side, 72 (81%) of 89 pairs were in agreement. Correlations (Cohen κ) of complete LAD were 0.65 (P < 0.001) on the right and 0.37 (P < 0.001) on the left. Correlations of total scores were 0.47 (P < 0.001) on the right and 0.41 (P < 0.001) on the left.

CONCLUSIONS

Moderate agreement was found between 3D US and 3D MRI LAD detection. More LADs and discordance were seen on the left.

Variability of the pubic arch architecture and its influence on the minimal levator hiatus area

OBJECTIVE

To investigate the association between the minimal levator hiatus (MLH) area at rest with its surrounding soft-tissue and bony structures in nulliparous asymptomatic women with a normal levator ani muscle.

METHODS

A subanalysis was undertaken of a prospective study of the appearance of the levator ani in asymptomatic nulliparous women conducted between September 2010 and September 2011. The subanalysis included women with a normal levator ani muscle. Three-dimensional ultrasonography volumes were used to obtain pelvic floor measurements.

RESULTS

The analysis included 56 women with mean age of 43.0±13.4years. The mean MLH area was 13.1±1.8cm(2) (range 9.0-17.3). The pubic arch angle had no influence on the MLH area (Pearson correlation coefficient r=0.13). Height and pubic arch length were positively correlated with the MLH area (r=0.26 [P=0.52] and r=0.50 [P<0.001], respectively).

CONCLUSION

The MLH size of nulliparous women varied widely and was positively correlated with the height and pubic arch length of the women. Therefore, caution is warranted when interpreting the MLH area as an indicator of a levator ani defect or a predictor of pelvic organ prolapse without taking a woman's pelvic bone characteristics into account.

Football practice and urinary incontinence: Relation between morphology, function and biomechanics

Current evidence points to a high prevalence of urinary incontinence among female athletes. In this context, this study aims to assess if structural and biomechanical characteristics of the pubovisceral muscles may lead to urine leakage. Clinical and demographic data were collected, as well as pelvic Magnetic Resonance Imaging. Furthermore, computational models were built to verify if they were able to reproduce similar biomechanical muscle response as the one measured by dynamic imaging during active contraction by means of the percent error. Compared to the continent ones (n=7), incontinent athletes (n=5) evidenced thicker pubovisceral muscles at the level of the midvagina (p=0.019 and p=0.028 for the right and left sides, respectively). However, there were no differences neither in the strength of contraction in the Oxford Scale or in the displacement of the pelvic floor muscles during simulation of voluntary contraction, which suggests that urine leakage may be related with alterations in the intrafusal fibers than just the result of thicker muscles. Additionally, we found similar values of displacement retrieved from dynamic images and numerical models (6.42 ± 0.36 mm vs. 6.10 ± 0.47 mm; p=0.130), with a percent error ranging from 1.47% to 17.20%. However, further refinements in the mechanical properties of the striated skeletal fibers of the pelvic floor muscles and the inclusion of pelvic organs, fascia and ligaments would reproduce more realistically the pelvic cavity.