MRI evaluation of the levator ani muscle: anatomic correlations and practical applications

A systematic review of clinical studies on dynamic magnetic resonance imaging of pelvic organ prolapse: the use of reference lines and anatomical landmarks

INTRODUCTION AND HYPOTHESIS

The aim of our study was to provide a systematic literature review of clinical studies on pelvic organ prolapse staging with use of dynamic magnetic resonance (MR) imaging.

METHODS

The databases EMBASE and PubMed were searched. Clinical studies were included in case they compared pelvic organ prolapse stages as assessed on dynamic MR imaging (using a reference line) with a standardized method of clinical prolapse staging.

RESULTS

Ten studies were included, which made use of seven different reference lines in relation to a wide variety of anatomical landmarks.

CONCLUSION

Only few studies have compared pelvic organ prolapse stages as assessed by dynamic MR imaging and clinical examination in a standardized manner. The available evidence suggests that prolapse assessment on dynamic MR imaging may be useful in the posterior compartment, but clinical assessment and dynamic MR imaging seem interchangeable in the anterior and central compartment.

The assessment of levator trauma: A comparison between palpation and 4D pelvic floor ultrasound

AIMS

Major morphological abnormalities of the pubovisceral muscle are observed in 10-20% of women symptomatic of pelvic floor disorders. Such defects arise in childbirth and are associated with prolapse. While they are clearly evident on 3D ultrasound and MR imaging, such defects can be difficult to detect clinically. We intended to compare findings on palpation with the results of ultrasound imaging.

MATERIAL AND METHODS

Fifty-five women were recruited in a prospective observational study and assessed by interview, vaginal examination by a trained pelvic floor physiotherapist, and 3D/4D pelvic floor ultrasound. The vaginal examination involved digital assessment of muscle strength (modified Oxford grading) and morphological abnormalities. The ultrasound examination involved acquisition of volume datasets taken at rest, on Valsalva and pelvic floor muscle contraction. Assessments were undertaken supine and after voiding. Ultrasound operator and physiotherapist were blind to each other's findings.

RESULTS

A comparison of 3D ultrasound and palpation was possible in 54 cases. Average Oxford grading was weakly associated with reduction in hiatal dimensions on contraction (r = -0.32, P = 0.024). A marked increase in hiatal dimensions detected on palpation was associated with increased hiatal area on Valsalva (P = 0.027). Defects were observed in 7/54 (13%) on ultrasound and in 10/55 (18%) on palpation. There was poor agreement between the methods, with only two defects picked up equally by both methods.

CONCLUSIONS

Palpation of the pubovisceral muscle correlates poorly with 3D/4D pelvic floor ultrasound imaging for the assessment of muscular defects.

3-DIMENSIONAL MAGNETIC RESONANCE IMAGING MODELING OF THE PELVIC FLOOR MUSCULATURE IN CLASSIC BLADDER EXSTROPHY BEFORE PELVIC OSTEOTOMY

PURPOSE

We provide a 3-dimensional (3D) model of the pelvic floor musculature in patients with classic bladder exstrophy using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Five male infants 1 day to 12 months old underwent MRI of the pelvis, which was compared to pelvic MRI of 1 male infant without pelvic floor abnormalities. Of the patients 3 were studied before primary closure and 2 before reclosure. None of the patients had a prior pelvic osteotomy. While the entire pelvic floor was imaged, special attention was paid to the contours of the levator ani muscle group which were drawn on T1-weighted axial and coronal images. The overlap of contours in these 2 planes was used to construct a 3D model of this muscle group. The diastasis of the pubic symphysis was also measured for all patients on a plain pelvic radiograph.

RESULTS

The levator ani muscle group conformed to an elliptical dome shape in the control. For the patients the 3D shape was somewhat irregular with an apparent kink in the ellipse. The elliptical shape of the group was described by a shape factor, s, which equals the ratio of the maximum height-to-the length of the base of the ellipse. The shape factor was equal to 0.176 in the control compared to a mean of 0.448 for the patients. There was no relationship between diastasis of the pubic symphysis and the extent of disproportionate curvature of the levator group.

CONCLUSIONS

To our knowledge this is the first qualitative description of the pelvic floor anatomy in bladder exstrophy using MRI. Our model gives further insights into the true pelvic floor anatomy in exstrophy cases and is the first to suggest that abnormalities in the pelvic floor may not correlate with abnormalities of the bony pelvis.

Pelvic Floor Magnetic Resonance Imaging after Neonatal Single Stage Reconstruction in Male Patients With Classic Bladder Exstrophy

PURPOSE

We evaluate a magnetic resonance imaging (MRI) protocol used to study the pelvic floor anatomy in male patients following neonatal single stage complete bladder exstrophy and epispadias repair with osteotomies.

MATERIALS AND METHODS

From 1996 to 2002, 9 males underwent surgical correction of bladder exstrophy and epispadias with osteotomies within 1 to 12 days of birth. Pelvic floor MRI was conducted comparing this group to 5 aged matched male patients with no pelvic anatomical abnormality who underwent MRI for other illness. We compared various measurement of pelvic musculature by unpaired Wilcoxon test.

RESULTS

Median followup was 3 years (range 0.5 to 5.3). All surgical procedures succeeded in closure of abdominal wall and genitalia defects. MRI data showed that in the exstrophy group symphyseal distance was significantly wider than that in controls (median 3.8 vs 1.1 cm). In addition, the levator ani fibers diverted more laterally (42 vs 22 degrees), the pelvic floor in coronal view was more flat (103 vs 80 degrees) and the anus was more anteriorly displaced (2.8 vs 4.4 cm). We also documented shorter anterior corporeal bodies in the exstrophy group (1 vs 2 cm). No statistical difference between the 2 groups was found in the dimensions of the levator and obturator muscles, sagittal angle of the pelvic floor, and the dimensions and angle of the posterior corporal bodies. Two patients achieved some degree of continence around the age of 4 years. They had the shortest symphyseal distance and sharpest angle of levator ani fiber divergence, and the bladder neck was more deeply located in the pelvic.

CONCLUSIONS

We applied novel MRI parameters to the pelvic floor anatomy providing a new quantifiable approach. Our protocol is feasible and reproducible, allowing for future comparison of the impact of different surgical modalities, and correlation between anatomical findings and continence.

Three-dimensional magnetic resonance imaging assessment of levator ani morphologic features in different grades of prolapse

OBJECTIVE

The study was undertaken to identify the morphologic changes in the levator ani in different grades of prolapse by using reconstructed three-dimensional models of magnetic resonance images (MRI) and to subclassify prolapse into different categories on the basis of their levator ani morphologic characteristics.

STUDY DESIGN

Sixty-one women were studied, 8 women in stage I, 15 women in stage II, 22 women in stage III, 7 women in stage IV prolapse, and 9 asymptomatic volunteers with stage 0 prolapse. Axial, sagittal, and coronal T2-weighted pelvic magnetic resonance scans were obtained with the patient in the supine position. The three-dimensional models were reconstructed from the source images by using manual segmentation and surface modeling. The morphologic characteristics of the puborectalis were assessed on these reconstructed models by measuring (1). the levator symphysis gap, (2). the width of the levator hiatus, and (3). the length of the levator hiatus. To assess the iliococcygeus, we measured (1). the maximum width of the iliococcygeus, (2). the direction of its fibers that was assessed by measuring the iliococcygeal angle, and (3) the levator plate angle. Nine nulliparous asymptomatic women were studied as controls.

RESULTS

Alterations in levator ani morphologic features are not dependent on the grade of the prolapse, and not all women with pelvic floor prolapse have abnormal morphologic features. In healthy control subjects, the iliococcygeal width measured less than 40 mm and the iliococcygeal angle measured less than 20 degrees. On the basis of the MRI findings, four patterns of changes in the levator ani have been identified. Both the levator symphysis gap and the levator hiatus, which is dependent on the puborectalis function, widen with increasing grade of prolapse.

CONCLUSION

It is possible to subclassify prolapse on the basis of morphologic changes in the levator ani by using MRI. This may be a very useful predictor as to which patients have recurrent prolapse develop after surgery.