M. OTCENASEK*, L. KROFTA*, V. BACA, R. GRILL, E. KUCERA*, H. HERMAN*, I. VASICKA*, J. DRAHONOVSKY* and J. FEYEREISL*

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1 Ultrasound Obstet Gynecol 2007; 29: Published online in Wiley InterScience ( DOI: /uog.4030 Bilateral avulsion of the puborectal muscle: magnetic resonance imaging-based three-dimensional reconstruction and comparison with a model of a healthy nulliparous woman M. OTCENASEK*, L. KROFTA*, V. BACA, R. GRILL, E. KUCERA*, H. HERMAN*, I. VASICKA*, J. DRAHONOVSKY* and J. FEYEREISL* *Institute for the Care of Mother and Child (UPMD), Department of Obstetrics and Gynecology and Center for Integrated Study of Pelvis (CISP), Charles University, Prague, Czech Republic KEYWORDS: 3D ultrasound; levator ani muscle; magnetic resonance imaging; obstetric trauma; prolapse; urinary stress incontinence; vaginal delivery ABSTRACT Objectives Obstetric trauma to the puborectal muscle seems to be an important cause of pelvic floor dysfunction in women. Due to the complicated three-dimensional (3D) arrangement of the pelvic structures, two-dimensional images are not sufficient to demonstrate its relationships in a complex fashion. Thus, we aimed to create a 3D computer model to visualize the normal female pelvic floor anatomy and to compare this with the anatomy after bilateral avulsion of the puborectal muscle following delivery. Methods We created two 3D computer models of the female pelvic floor, one of a healthy nulliparous woman and the other of a woman with bilateral puborectal muscle avulsion after vaginal delivery. The data for the models were obtained from magnetic resonance imaging examinations and the following structures were depicted: pelvic bones, puborectal muscle, internal obturator muscle, urethra, urinary bladder, vagina and rectum. The models were compared. Results The models allowed us to demonstrate in three dimensions changes in the puborectal muscle after avulsion. Its relations to the bone, internal obturator muscle, perineal membrane and the deep part of the external anal sphincter were modeled and differences from the normal non-injured anatomy were demonstrated. Avulsion altered the support to the whole endopelvic fascia and destabilized both the anterior and the posterior vaginal walls. Conclusions The use of 3D technology including modeling allows for the acquisition of new knowledge and aids in the understanding of both normal and pathological pelvic anatomy. Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION The puborectal muscle is considered a key structure for the proper functioning of the pelvic floor. Damage can manifest as pelvic floor dysfunction, for example, urinary stress incontinence 1 and pelvic organ prolapse 2. Injury to the muscle is caused mainly by vaginal birth 2,3 due to distension of the muscle to more than three times its resting length, caused by the passage of the fetal head 4. The puborectal muscle extends from both sides of the back plane of the pubic bone and its fibers surround the urethra, vagina and rectum 5,6. The course of its fibers is well depicted on magnetic resonance imaging (MRI) and three-dimensional (3D) ultrasound 7 10 (Figure 1). The fibers at the cranial part of the muscle are contiguous with the iliococcygeus muscle, and those at the caudal part are contiguous with the deep part of the external anal sphincter. Given the complicated 3D arrangement of the structures in the pelvis, two-dimensional (2D) images are not sufficient to demonstrate the relationships of the puborectal muscle in a complex fashion 11,12. Furthermore, while 3D imaging works well with some rendering methods, it is not optimal for imaging Correspondence to: Dr M. Otcenasek, Institute for the Care of Mother and Child (UPMD), Podolske nabrezi 157, Prague 4-Podoli, Czech Republic ( otcenasm@volny.cz) Accepted: 25 January 2007 Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

2 Puborectal muscle avulsion 693 Figure 1 T2-weighted axial magnetic resonance image showing the normal contour of the puborectal muscle (PM) and its insertion on the posterior aspect of the pubic bone (PB, arrow). OI, obturator internus; R, rectum; U, urethra; V, vagina. all structures simultaneously. Thus, we created a 3D computer model, containing virtual surfaces of all structures, to visualize the normal anatomy and to compare this with the anatomy after bilateral avulsion of the puborectal muscle following delivery. Figure 2 Ultrasound image (volume contrast imaging mode; slice thickness, 3 mm), in the same plane as that shown in Figure 1, in a patient with avulsion of the puborectal muscle. The muscle (arrows) cannot be separated clearly from the rectovaginal septum (*). However, it is obvious that no portion of the muscle lies anteriorly to the pubic bone (PB) and the avulsion is clearly apparent. R, rectum; U, urethra; V, vagina. METHODS We examined a woman 15 months after vaginal delivery of her first and only child (birth weight, 3710 g; length, 50 cm). She had had a difficult, albeit short (10 min), second stage of labor during which heavy fundal pressure (the patient s description) was applied to expedite delivery because of suspected fetal bradycardia on cardiotocography; and an uncomplicated mediolateral left-sided episiotomy. She presented with thirddegree intermittent uterine prolapse according to the Baden Walker classification 13, and with second-degree paravaginal cystocele ( traction-type cystocele) but without clinical rectocele 13,14. She reported no episodes of urinary or fecal incontinence. The resting tone and maximum squeeze of the anal sphincter were normal. The introitus was not dilated markedly and the distance from the middle of the external urethral orifice to the posterior fourchette was 25 mm when the uterus was repositioned. On vaginal examination, no puborectal muscles could be palpated in their normal locations on either side. 3D ultrasound examination (GE Voluson Expert 730 ultrasound machine, GE Medical Systems, Milwaukee, WI, USA) showed bilateral puborectal muscle defects with abnormal vaginal contours (Figure 2). We produced an axial T2-weighted MRI image (1.5 T; slice thickness, 3mm; gap, 1 mm; pelvic phased-array coil) from the third vertebra of the sacral bone (S3) to the lower region of the external anal sphincter (Figure 3). The examination Figure 3 T2-weighted axial magnetic resonance image showing bilateral avulsion of the puborectal muscle (PM) from the pubic bone (PB). The anterior part of the muscle is not connected to the PB, but is retracted laterally and points to the medial aspect of the internal obturator muscle (OI, arrow). R, rectum; U, urethra; V, vagina. was performed with the patient in a supine position after repositioning of the uterus, without contrast material, and the bladder was filled with 150 ml of sterile saline. To create the model, the position of each image was reconstructed according to the coordinates generated by

3 694 Otcenasek et al. the MRI machine. In each image, the boundary of each structure was labeled (bone, levator ani muscle, internal obturator muscle, urethra, urinary bladder, vagina and rectum). The contour of the structures was then applied to the construction of a surface model using Lightwave 7.5 (NewTec, San Antonio, TX, USA) 15 (Figures 4 and 5). These findings were then compared with a surface model of the pelvis of a 26-year-old healthy nulliparous female, who was selected (on the basis of the quality of the model produced) from a group of 15 women examined who fulfilled the following criteria: under 30 years of age, without signs of descent on vaginal examination, and no subjective evidence of pelvic floor dysfunction 16. RESULTS Normal anatomy of the sacrospinous ligaments and the iliococcygeus muscles was found on both left and right sides, in both women. In the parous woman, we did not observe observe any fibers of the levator ani muscle, which would normally be attached to the pubic bone; in the model of the healthy woman, this attachment was clearly shown. In the parous woman, the muscle fibers encircling the rectum at the level of the puborectal muscle were retracted dorsolaterally and extended to the medial aspects of the internal obturator muscle (Figures 2 and 3). The perineal membrane and the deep part of the external anal sphincter were also intact (Figures 4 and 5). Differences between the models were demonstrated in the shape of the vagina, with the lateral sulcus of the vagina adhering closely to the medial aspect of the internal obturator muscle and pointing slightly dorsally towards the remnants of the damaged puborectal muscle in the parous woman. Furthermore, the anorectal angle was more pronounced in the parous woman, being 140 compared with 90 in the healthy woman. DISCUSSION Figure 4 Rendered image from the three-dimensional computer model showing the normal anatomy of the puborectal muscle (PM) and its relationship to neighboring structures. B, perineal body; IC, iliococcygeus muscle; OI, obturator internus; PB, pubic bone. Figure 5 Rendered image from the three-dimensional computer model showing bilateral avulsion of the puborectal muscle (PM). The anterior part of the PM has completely lost its connection to the pubic bone (PB). Its fibers are retracted dorsolaterally. The deep and superficial portions of the external anal sphincter are similar and do not show any signs of trauma. B, perineal body; IC, iliococcygeus muscle; OI, obturator internus; U, urethral opening in perineal membrane; V, vaginal opening between perineal membrane and perineal body. Arrows show the original points of insertion of both arms of the puborectal muscle on the pubic bone. The modeled case demonstrates an example of complete avulsion of the puborectal muscle from its normal insertion on the inferior pubic ramus. The fact that the residual muscle fibers did not retract to the rectum in a straight line, but pointed slightly laterally to the internal obturator muscle and appeared to have some connection to their medial aspects is surprising. This could indicate the existence either of a partial lateral attachment of the puborectal muscle to the internal obturator muscle that retained its function after ventral attachment to the bone was destroyed, or of fibers which simply followed the course of the fascia of the ischiorectal fossa (Figure 6). Further anatomical studies are needed to answer this question. Static MRI cannot evaluate the mechanical properties of the avulsed muscle as it relates to the internal obturator muscle and cannot predict its behavior at the point of increased intra-abdominal pressure, i.e. on Valsalva maneuver. There is evidence from 3D ultrasound imaging to suggest that the avulsed puborectal muscle moves far away from the obturator muscle and leaves the urogenital hiatus wide open 17. The width of the introitus is affected by another pelvic floor muscle, namely the deep part of the external anal sphincter. This is a U-shaped muscle that surrounds the rectum and vagina. The anterior arms insert into the superior aspect of the perineal membrane. The muscle closes the introitus and propels the anus anteriorly (Figure 4). In the modeled case, this muscle was intact (similar to in normal women). This was also reflected in the normal diameters of the introitus on clinical examination. The endopelvic fascia is anchored to the puborectal muscle. Hence, avulsion alters the support to the whole

4 Puborectal muscle avulsion 695 precisely by MRI. On 2D MRI, the impression might be made that this muscle is the puborectal muscle and that its ventral margin is avulsed. Such pitfalls emphasize the need to evaluate the puborectal muscle in the context of its neighboring regions. In healthy nulligravid women, clear insertion of the puborectal muscle to the pubic bone is visible in 81% of cases; the remaining 19% have no clear margin between the internal obturator muscle and the puborectal muscle 19. The difference between normal muscle anatomy and that of the injured muscle lies in the fact that the medial aspect of the puborectal muscle heads strictly forward in non-injured cases, whereas it bends laterally in avulsed cases. Construction of 3D computer models is expensive and labor intensive, but the resulting models yield a large amount of information that simply cannot be extracted from 2D studies. Further use of mathematical modeling may be useful in the future to help quantify the relationships of anatomy, mobility and pressure gradients in order to resolve questions of continence and pelvic floor prolapse. ACKNOWLEDGMENTS Figure 6 T2-weighted axial magnetic resonance image depicting the relationship of the puborectal muscle (PM) to the internal obturator muscle (OI) in healthy women. The open arrow shows the insertion of the PM on the pubic bone (PB). From the point of insertion, the PM and the OI run in close apposition and eventually divide (filled arrow) and define the ventral limits of the ischiorectal fossa. The medial aspect of the OI is covered with a fascia, which crosses over into the lateral aspect of the PM (ischiorectal fascia). It is possible that after avulsion, the muscle fibers follow the course of the ischiorectal fascia and head towards the OI. R, rectum; U, urethra; V, vagina. endopelvic fascia and destabilizes both the anterior and the posterior vaginal walls. Lateral support of the vaginal wall depends on the endopelvic fascia and puborectal muscle. This study has shown that the clinical finding of paravaginal cystocele (vaginal rugae are preserved) on vaginal examination can result from either defective attachment of the vagina to the puborectal muscle (fascial defect) or from defective attachment of the muscle to the bone (avulsion). Until now, paravaginal cystocele was understood to be the result of only a fascial tear 18. Unfortunately, current imaging techniques cannot visualize fascial tears, but avulsion can be visualized with great accuracy on both MRI and 3D ultrasound examination 3,10. In this study, spatial analysis revealed the major areas of misinterpretation seen in 2D transverse MRI images: (1) the avulsed fibers leading to the medial aspect of the internal obturator muscle, thus mimicking the normal contour of the iliococcygeus portion of the levator ani (this muscle inserts into the tendineus arc of the levator ani); (2) the deep part of the external anal sphincter inserting into the perineal membrane, which cannot be identified This work was supported by the Czech Ministry of Health, grant No. IGA NR Artwork was produced by Ivan Helekal, anatomical illustrator, academic painter. REFERENCES 1. Dietz H, Steensma A. The prevalence of major abnormalities of the levator ani in urogynaecological patients. BJOG 2006; 113: Dietz HP, Lanzarone V. Levator trauma after vaginal delivery. Obstet Gynecol 2005; 106: 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: Lien KC, Mooney B, DeLancey JO, Ashton-Miller JA. Levator ani muscle stretch induced by simulated vaginal birth. Obstet Gynecol 2004; 103: DeLancey J. Anatomy. In Textbook of Female Urology and Urogynecology, Cardozo L, Staskin D (eds). Isis Medical Media: London, UK, 2001; Nichols DH, Randal CL. Posterior colporrhaphy and ierineorrhaphy. In Vaginal Surgery, Nichols DH, Randal CL (eds). Wiliams and Wilkins: Philadelphia, PA, 1996; Strohbehn K, Ellis JH, Strohbehn JA, DeLancey JO. Magnetic resonance imaging of the levator ani with anatomic correlation. Obstet Gynecol 1996; 87: Tunn R, Paris S, Fischer W, Hamm B, Kuchinke J. Static magnetic resonanace imaging of the pelvic floor muscle morphology in women with stress urinary incontinence and pelvic prolapse. Neurourol Urodyn 1998; 17: Tunn R, Delancey JO, Howard D, Thorp JM, Ashton-Miller JA, Quint LE. MR imaging of levator ani muscle recovery folowing vaginal delivery. Int Urogynecol J Pelvic Floor Dysfunct 1999; 10: Dietz HP, Shek C, Clarke B. Biometry of the pubovisceral muscle and levator hiatus by three-dimensional pelvic floor ultrasound. Ultrasound Obstet Gynecol 2005; 25:

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