The levator ani muscle complex provides the majority of pelvic support. Anatomic variants have been occasionally reported in limited series of nullipa

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1 Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at ORIGINAL RESEARCH n GENITOURINARY IMAGING Pierre Loubeyre, MD Michele Copercini, MD Patrick Petignat, MD Jean Bernard Dubuisson, MD Levator Ani Muscle Complex: Anatomic Findings in Nulliparous Patients at Thin-Section MR Imaging with Double Opacifi cation 1 Purpose: Materials and Methods: To determine levator ani muscle complex anatomic findings in nulliparous patients at magnetic resonance (MR) imaging examinations performed with opacification of the vagina and rectum with ultrasonographic gel. The institutional review board approved this retrospective study, and the informed consent requirement was waived. Findings from pelvic MR imaging examinations with double opacification in 123 consecutive nulliparous patients (mean age, years; age range, years) who were suspected of having endometriosis were reviewed. The pubococcygeal muscles were analyzed on coronal sections obtained through the middle part of the vagina, perineal body, and anal canal. The puborectalis muscles were analyzed on coronal sections obtained through the perineal body. The iliococcygeal muscles were analyzed on coronal sections obtained through the rectum. Miscellaneous findings such as visibility of deep transverse muscles of the perineum, perineal body, and focal muscle defects were also noted. Results: Conclusion: In 56% (69 of 123) of patients, at least one morphologic variant (thinning or aplasia) of a muscle of the levator ani complex was noted. Variants of puborectalis muscles were noted in 6% of patients. Variants of iliococcygeal muscles were noted in 13%. Variants of pubococcygeal muscles were noted in 32% at the anal canal level, in 49% at the perineal body level, and in 49% at the vaginal level. Variants of pubococcygeal muscles were noted on the left side in 53 patients (77% of pubococcygeal muscle variants). Numerous morphologic variants of the levator ani muscle complex are noted at coronal thin-section MR imaging with double opacification. Most involve the pubococcygeal muscle on the left side at perineal body and vaginal levels. Whether some of these anatomic findings may favor prolapse after vaginal birth may be questioned. q RSNA, From the Departments of Imaging (P.L.) and Obstetrics and Gynecology (M.C., P.P., J.B.D.), Geneva University Hospitals, Rue Gabrielle-Perret-Gentil, 1211 Geneva 14, Switzerland. Received June 20, 2011; revision requested July 18; revision received August 12; accepted September 2; fi nal version accepted September 19. Address correspondence to P.L. ( Pierre.loubeyre@hcuge.ch ). Supplemental material: /suppl /doi: /radiol /-/dc1 q RSNA, radiology.rsna.org n Radiology: Volume 262: Number 2 February 2012

2 The levator ani muscle complex provides the majority of pelvic support. Anatomic variants have been occasionally reported in limited series of nulliparous women ( 1 ). Pelvic magnetic resonance (MR) imaging with opacification of the vagina and rectum with ultrasonographic (US) gel allows clear visualization of pelvic anatomic structures. This technique has been advocated for posterior deeply infiltrating endometriosis diagnosis ( 2 ). Furthermore, because of vaginal and rectal distention with US gel, pubovisceral muscles are smoothed out, which allows muscular morphology to be clearly demonstrated. The purpose of our study was to determine levator ani muscle complex anatomic findings in nulliparous patients at MR imaging examinations performed with opacification of the vagina and rectum with US gel. Materials and Methods Patients The institutional review board approved this retrospective study, and the informed consent requirement was waived. Pelvic MR imaging examinations with vaginal and rectal opacification in Advances in Knowledge n Numerous morphologic appear- ances or variants of the levator ani muscle complex are noted in nulliparous patients at coronal thin-section MR imaging with double opacification. n In 56% (69 of 123) of patients, at least one morphologic variant of a muscle of the levator ani complex was noted; most involved the pubococcygeal muscle on the left side at perineal body and vaginal levels on coronal sections. n Morphologic variants of puborec- talis muscles were noted in 6% (seven of 123) of patients; morphologic variants of iliococcygeal muscles were noted in 13% (16 of 123). 123 consecutive nulliparous patients (mean age, years; age range, years) who were suspected of having endometriosis were retrieved from our picture archiving and communication system, and appearance of the levator ani muscle complex, appearance of deep transverse muscle of the perineum, and appearance of the perineal body were analyzed. No patient was known to have pelvic floor dysfunction. MR Imaging Technique With the use of a cannula, 50 and 150 ml of US gel was injected into the vagina and the rectum, respectively. MR imaging was performed with a 1.5-T magnet (Magnetom Avanto; Siemens Medical Solutions, Erlangen, Germany) and a pelvic phased-array coil, with patients in the supine position. MR imaging was initiated 15 minutes after a muscle relaxant (1 ml butylscopolamine, Buscopan; Boehringer-Ingelheim, Ingelheim, Germany) was administered intramuscularly, when there was no contraindication, to avoid ghosting artifacts caused by bowel peristalsis. No contrast material enhanced sequence was performed. The standard imaging protocol included T2-weighted turbo spin-echo sequences (repetition time, 6000 msec ; echo time, 110 msec; matrix, ; field of view, mm; section thickness, 3 mm; intersection gap, 0.3 mm; voxel, mm; turbo factor, 15) in sagittal, coronal, and transverse planes. Methods For each patient, coronal MR images were reviewed. Coronal images appeared to be well adapted to depict the U shape of pubococcygeal and iliococcygeal muscles. Coronal sections obtained through the middle part of the vagina, perineal body, anal canal, and postanal rectum were analyzed. Levels of coronal images were checked on a midsagittal section (Fig E1, Appendix E1 [online]). The pubococcygeal muscles were analyzed on three representative coronal sections respectively obtained through the middle part of the vagina (anterior level), perineal body (intermediate level), and anal canal (posterior level). The puborectalis muscles were analyzed on a coronal section obtained through the perineal body. The iliococcygeal muscles were analyzed on a coronal section obtained through the rectum. Muscle morphology was analyzed by two radiologists (P.L. and M.C., each with more than 10 years of MR experience) who reached a consensus such as follows: Aplasia (missing muscle) was nonvisible muscle or a line instead of the missing muscle ( Figs 1, 2, 3, E2, E3, E4 [online]). Unilateral thinning was clear muscle asymmetry, with muscle thickness on one side visually estimated to be 50% or less of that of muscle thickness of the opposite side ( Figs 4, 5, E5, E6, E7, E8 [online]). Bilateral thinning was clear thinning of muscles on both sides ( Figs 6, E9 [online]). Thicknesses of pubococcygeal and puborectalis muscles were measured on coronal sections obtained through the perineal body. Thinning of pubococcygeal muscle was considered when muscle thickness was 2 mm or less (thinnest of the muscle) ( Figs 5, E5, E6 [online]). Bilateral pubococcygeal muscle thinning on coronal sections obtained through the perineal body was considered when muscle thickness was 2 mm or less on both sides ( Figs 6, E9 [online]). Unilateral thinning of puborectalis muscle was considered when muscle thickness on one side measured 50% or less of that of muscle thickness on the other side (Fig E7 [online]). Miscellaneous findings such as visibility of deep transverse muscles of the perineum, perineal body, fusion Published online before print /radiol Content code: Radiology 2012; 262: Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/ interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript fi nal version approval, all authors; literature research, all authors; clinical studies, all authors; and manuscript editing, all authors Potential confl icts of interest are listed at the end of this article. Radiology: Volume 262: Number 2 February 2012 n radiology.rsna.org 539

3 Figure 1 Figure 3 Figure 5 Figure 1: Coronal MR image in 20-year-old woman shows aplasia of left pubococcygeal muscle (arrow) at level of perineal body ( ). R = rectum, V = vagina. Figure 2 Figure 3: Coronal MR image obtained at level of rectum (R) in 32-year-old woman shows aplasia of iliococcygeal muscles. A line is hardly visible instead of iliococcygeal muscles (triple arrows). Figure 4 Figure 5: Coronal MR image in 29-year-old woman shows thinning of right pubococcygeal muscle (arrow) at level of perineal body ( ), with muscle thickness less than 2 mm. V = vagina. Figure 6 Figure 2: Coronal MR image in 22-year-old woman shows aplasia of left puborectalis muscle (double arrows) at level of perineal body ( ). Note thinning of left pubococcygeal muscle (arrow). Deep transverse muscles of the perineum (dotted arrows) were not clearly visible. R = rectum, V = vagina. of puborectalis muscles to the perineal body, and focal muscle defects were also noted. Results In 56% (69 of 123) of patients, at least one morphologic variant of a muscle of the levator ani complex was noted ( Table 1 ). No isolated variant of puborectalis or iliococcygeal muscles was noted without concomitant variant of pubococcygeal Figure 4: Coronal MR image in 26-year-old woman shows thinning of left pubococcygeal muscle (arrow) at level of vagina (V). muscle. Morphologic variants of puborectalis muscles were noted in 6% (seven of 123) of patients. Morphologic variants of iliococcygeal muscles were noted in 13% (16 of 123). Morphologic variants of pubococcygeal muscles were noted in 32% (39 of 123) of patients at the anal canal level, in 49% (60 of 123) at the perineal body level, and in 49% (60 of 123) at the vaginal level. Percentage of muscle thinning was superior to 80% compared with muscle aplasia. At the vaginal level, Figure 6: Coronal MR image in 36-year-old woman shows bilateral thinning. Thinning of pubococcygeal (arrows), puborectalis (double arrows), and iliococcygeal (not shown) muscles are at level of perineal body ( ). Hypoplasia of perineal body was noted. R = rectum. muscle thinning occurred in 82% (49 of 60) of patients, muscle aplasia occurred in 15% (nine of 60), and a combination of muscle thinning and aplasia occurred in 3% (two of 60). At the perineal body level, muscle thinning occurred in 85% 540 radiology.rsna.org n Radiology: Volume 262: Number 2 February 2012

4 Table 1 Levator Ani Muscle Complex Anatomic Findings on Coronal Thin-Section MR Images in 123 Consecutive Nulliparous Patients Levator Ani Muscle * Bilateral Normal Appearance Left Thinning Bilateral Thinning Left Aplasia Left Aplasia and Right Thinning Bilateral Aplasia Right Thinning Right Aplasia Pubococcygeal (vagina) Pubococcygeal (perineal body) Pubococcygeal (anal canal) Puborectalis (perineal body) Iliococcygeal (rectum) Note. Data are numbers of patients. * Level of coronal section is in parentheses. Figure 7 Figure 7: Coronal MR images in 19-year-old woman show aplasia and thinning of left pubococcygeal muscle (arrows). Aplasia of left pubococcygeal muscle is seen (left) at level of vagina (V) and (middle) perineal body ( ), and (right) thinning of left pubococcygeal muscle is seen at level of anal canal. R = rectum. (51 of 60) of patients, muscle aplasia occurred in 8% (five of 60), and a combination of muscle thinning and aplasia occurred in 7% (four of 60). At the anal canal level, muscle thinning occurred in 95% (37 of 39) of patients, muscle aplasia occurred in 2.5% (one of 39), and a combination of muscle thinning and aplasia occurred in 2.5% (one of 39). Different combinations of unilateral or bilateral muscular thinning and aplasia were noted ( Figs 7, 8, 9, E10 [online]). Morphologic variants of pubococcygeal muscles were the more frequent variants. They were noted on the left side in 77% (53 of 69) of cases ( Table 2 ), on the right in 3% (two of 69), and on both sides in 20% (14 of 69). In most cases, the pubococcygeal muscle was involved at the vaginal and perineal body levels on coronal sections. Otherwise, miscellaneous findings were encountered. Nonvisibility of the deep transverse muscle of the perineum occurred on both sides in 26 patients ( Figs 2, E3, E7 [online]), on the left side in 14 patients ( Fig 10 ), and on the right side in three patients ( Fig 10 ). Nonclear fusion of puborectalis muscles to the perineal body was seen in seven patients (Fig E11 [online]). Hypoplasia of the perineal body occurred in one patient. Focal muscle defects of pubococcygeal muscles were noted in three patients (Fig E12 [online]). Discussion Studies for assessing anatomic variants of the levator ani muscle complex may provide useful insight into the pathophysiology of prolapse. Pelvic organ prolapse and/or pelvic floor descent occur when defects or disruption in the support structures appear. Women with prolapse more often have defects in the levator ani compared with women without prolapse with group matching for age ( 3 ), and vaginal delivery has been well established as a substantial risk factor for levator ani muscle injuries or weakness. Anteromedial uni- or bilateral defects of the pubovisceral muscle have been found at translabial US in 15.4% of parous women who had delivered vaginally and were associated with anterior and central compartment prolapse ( 4 ). In a series of 135 women (mean age, 56.6 years), with normal support determined by using pelvic organ prolapse quantification examination, major levator ani defects (more than half of the muscle missing) were Radiology: Volume 262: Number 2 February 2012 n radiology.rsna.org 541

5 Figure 9 Figure 9: Coronal MR images in 37-year-old woman show aplasia and thinning of pubococcygeal (arrows) and iliococcygeal (triple arrows) muscles. (Left) Aplasia of right pubococcygeal muscle at level of vagina (V), (middle left) aplasia of left pubococcygeal muscle and thinning (muscle thickness,, 2 mm) of right pubococcygeal muscle at level of perineal body ( ), (middle right) aplasia of pubococcygeal muscle at level of anal canal, and (right) thinning of iliococcygeal muscle are shown. R = rectum. Figure 8 Figure 8: Coronal MR images in 25-year-old woman show aplasia and thinning of pubococcygeal muscles (arrows). Left: Aplasia of left pubococcygeal muscle and thinning of right pubococcygeal muscle (muscle thickness,, 2 mm) is seen at level of perineal body ( ). Right: Thinning of pubococcygeal muscles is seen at level of anal canal. R = rectum. noted in 16% of patients, and minor levator ani defects (less than half of the muscle missing) were found in 22% ( 3 ). In this population, most patients were parous (mean vaginal parity, [standard deviation]) and postmenopausal. When considering defects after a woman s first vaginal birth, pubovisceral defects (from partial tear of the pubococcygeal sling to complete defect) were more commonly seen than iliococcygeal defects. In another study ( 5 ), no levator ani defects were identified in 80 nulliparous patients but were noted in 20% of the vaginally primiparous group, and most defects were identified in the pubovisceral portion of the levator ani, just lateral to the vagina. Nonetheless, no clear levator ani muscle anatomic findings or variants in nulliparous women have been reported to favor such injuries. MR imaging based series assessing anatomy of the levator ani muscle complex in young nulliparous women are limited. Quantification of muscle mass on MR-based three-dimensional modeling of the normal pelvic floor, in 10 young nulliparous women, concluded that muscle morphology and volume is relatively uniform among healthy young women ( 6 ). Variations in levator ani thickness have been reported in a series of 20 continent young nulliparous patients, with a minimum thickness value of 4.0 mm in the paravaginal region without right or left side difference ( 1 ). To our knowledge, anatomic variants of deep transverse muscle of the perineum have not been previously reported in series of nulliparous patients. We noted nonvisibility of deep transverse muscle of the perineum on at least one side in 35% (43 of 123) of patients. Our study had several limitations: All of our patients were referred for suspicion of endometriosis. This represented a referral bias. Muscle distortion might be noted in severe endometriosis. However, this would not explain the fact that most anatomic muscular morphologic variants were noted on the left side. Position of the patients in the magnet may also be suggested for the appearance of muscle thinning. We did not assess interobserver variability in our descriptors. We considered a normal muscle thickness of 2 mm, without a reference to substantiate this as a threshold for abnormal. One might consider that axial plane should have been assessed for puborectalis thinning. Coronal plane, which is perpendicular to the longitudinal puborectalis muscle 542 radiology.rsna.org n Radiology: Volume 262: Number 2 February 2012

6 Figure 10 gel. We found numerous morphologic appearances or variants of the levator ani muscle complex. Most involved pubococcygeal muscle on the left side at perineal body and vaginal levels on coronal sections. Moreover, we noted anatomic variants of deep transverse muscle of the perineum in several women. Whether some of these anatomic findings may favor prolapse after vaginal birth may be questioned. Disclosures of Potential Conflicts of Interest: P.L. No potential conflicts of interest to disclose. M.C. No potential conflicts of interest to disclose. P.P. No potential conflicts of interest to disclose. J.B.D. No potential conflicts of interest to disclose. Figure 10: Coronal MR images show nonvisibility of deep transverse muscles of perineum (dotted arrows). Right and left deep transverse muscles of perineum were not seen respectively in (a) 23-year-old woman and (b) 37-year-old woman. Note thinning (arrow) of left pubococcygeal muscle at level of perineal body ( ). R = rectum, V = vagina. Table 2 Localization of Morphologic Variants of Left Pubococcygeal Muscle in 53 Patients Level of Pubococcygeal Muscle on Coronal Sections No. of Patients Vagina 6 Vagina and perineal body 20 Vagina, perineal body, and anal 18 canal Vagina and anal canal 1 Perineal body 2 Perineal body and anal canal 5 Anal canal 1 axis, is adapted to image muscle thickness or morphology. However, detachment of the puborectalis from the pubic bone, which may be noted in parous women who had delivered vaginally and were not under the scope of this study, is not assessed with the coronal plane. Finally, there may be a concern about muscle deformation due to the pressure of extended vagina and rectum because of the amount of gel. However, this would not explain the fact that most anatomic muscular morphologic variants were noted on the left side. Without distention with US gel, pubovisceral muscles could not be smoothed out and muscular morphology would not be clearly demonstrated. This might be a reason why these variants have not been demonstrated before. In conclusion, we reported anatomic levator ani muscle complex anatomic findings or variants in a large series of consecutive young nulliparous patients at high-spatial-resolution MR imaging with opacification of the vagina and rectum with US gel. This technique allowed clear assessment of different muscles of the levator ani complex and demonstration of potential anatomic variants because muscles are smoothed out by using vaginal and rectal distention with References 1. Tunn R, Delancey JO, Howard D, Ashton- Miller JA, Quint LE. Anatomic variations in the levator ani muscle, endopelvic fascia, and urethra in nulliparas evaluated by magnetic resonance imaging. Am J Obstet Gynecol 2003 ; 188 ( 1 ): Loubeyre P, Petignat P, Jacob S, Egger JF, Dubuisson JB, Wenger JM. Anatomic distribution of posterior deeply infiltrating endometriosis on MRI after vaginal and rectal gel opacification. AJR Am J Roentgenol 2009 ; 192 ( 6 ): DeLancey JO, Morgan DM, Fenner DE, et al. Comparison of levator ani muscle defects and function in women with and without pelvic organ prolapse. Obstet Gynecol 2007 ; 109 ( 2 pt 1 ): Dietz HP, Steensma AB. The prevalence of major abnormalities of the levator ani in urogynaecological patients. BJOG 2006 ; 113 ( 2 ): DeLancey JO, Kearney R, Chou Q, Speights S, Binno S. The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery. Obstet Gynecol 2003 ; 101 ( 1 ): Fielding JR, Dumanli H, Schreyer AG, et al. MR-based three-dimensional modeling of the normal pelvic floor in women: quantification of muscle mass. AJR Am J Roentgenol 2000 ; 174 ( 3 ): Radiology: Volume 262: Number 2 February 2012 n radiology.rsna.org 543