3.0-T MRI-based Study On Female Pelvic Floor Dysfunction

Female pelvic floor dysfunction is a general term applied to a wide variety of clinical conditions, most commonly stress urinary incontinence (SUI), pelvic organ prolapse (POP), and anal incontinence. Multiple congenital and acquired risk factors are associated with pelvic floor failure, including altered collagen metabolism, female sex, vaginal delivery, menopause, and advanced age. Up to20%of the female population will have symptoms of POP and/or UI severe enough to require surgery. Another one out of six women will undergo additional surgery because of postoperative POP recurrence.Historically, fluoroscopic defecography, first described in1952, has played an important role in diagnosis of functional abnormalities of the pelvic floor, but the technique has inherent limitations. Primarily, depiction of pelvic soft tissues is restricted: the tissues can be enhanced only by administration of contrast material into several anatomic compartments, such as the vagina, bladder, small intestine, and peritoneum. This step inevitably increases the invasiveness of the examination. In addition, the fluoroscopic technique involves exposing the patient to ionizing radiation. With the development of magnetic resonance imaging (MRI) technology, dynamic MRI of the pelvic floor has become an important alternative for the diagnosis of complex combined pelvic floor disorders. Since its first introduction by Yang et al and Kruyt et al in1991, MRI has increasingly replaced evacuation proctography for evaluation of outlet obstruction.Till now, there is no international standardized pelvic floor MR imaging protocol that can be used for women with symptoms and/or signs of pelvic floor dysfunction. The patient preparation, examination technique, as well as reference lines for the evaluation of MRI are still not standardized and findings differ widely in the current literature.The purpose of this study is to develop a one-stop procedure based on3.0-T MR dynamic imaging to exam female floor structure and to determine whether female pelvic dysfunction is associated with specific pelvic floor abnormalities.Materials and Methods:1. A pilot study was performed to establish the MRI protocol and the reliability of the measurement based on reference PCL was tested.MR imaging was performed with the patient supine in a3.0-T MR imaging unit (Achieva3.0T X-series, Philips Medical Systems, Best, the Netherlands) by using a pelvic phased-array coil. No oral or intravenous contrast agent was administered. All patients were asked to void2hours before the examination. The rectum was opacified with60mL of ultrasonographic gel mix with0.1ml paramagnetic contrast media gadolinium through a catheter.The four dynamic phases were rest, maximal sphincter contraction (squeeze), defecation and maximal strain.The dynamic defecation examination was completed with an sagittal single shot T2-weighted fast spin-echo sequence. The scan was repeated20times on the central middle line plane. The parameters were as follows:TR/TE:1084/70ms; FOV,320mm; slice thickness,5mm; matrix,200×167.Analysis of dynamic MR images.-In the sagittal plane, the PCL, which extends from the inferior border of the symphysis pubis anteriorly to the tip of the coccyx posteriorly, was used as the reference line. For each participant, the descent of the bladder neck, bladder base, uterus, and anorectal junction below the PCL was recorded.A experienced radiologist and a trained intern were enrolled to measure the H line, M line and ano-rectal angle. To evaluate agreement between measurements, intraclass correlation coefficients (ICCs) with their95%CI were calculated. ICC values <0.20were considered as poor, values0.21-0.40as fair, values0.41-0.60as moderate, values0.61-0.80as good and values>0.80as excellent. SPSS version19.0(SPSS Inc., Chicago, IL, USA) statistical software for Windows was used for statistical analyses.2. From May2010to November2013,230consecutive patients who had symptoms of chronic constipation, feeling of incomplete evacuation, pain during defecation, and/or faecal incontinence were enrolled. All the patients were referred by certified colorectal surgeons and underwent prior outpatient examinations.All the patients gave informed consent. Approval of the hospital ethical committee had been granted as part of an ongoing study. All the patients were performed both MR scan and X-ray defecography. The MR scans were followed the protocol established previously. The X-ray unit used for defecography was a Winscope2000X-ray TV system (Toshiba Medical Systems Otawara, Japan). The X-ray defecation was also included four dynamic phases:rest, maximal sphincter contraction (squeeze), defecation and maximal strain.MR features of pelvic floor dysfunction, which include rectocele, enterocele, uterine prolapse, cystocele, rectal prolapse and rectal intussusception, were evaluated and recorded. The posterior pelvic apartment abnormal features found in MRI were compared with those found in X-ray defecography.3. The left and right sides of the pubovisceral muscle were scored separately, as follows:0, normal appearance of the muscle;1, identifiable connection of the muscle to the pubis but <50%of expected muscle bulk missing;2,≥50%of expected muscle bulk missing but the presence of a connection of the muscle to the pubis; and3, complete detachment of the muscle from the pubis. A total score for the two sides (0-6) was then assigned and categorized as no defect (0), minor pubovisceral avulsion (1-3) or major pubovisceral avulsion (4-6, or a unilateral score of3). All cases were analyzed by two experienced radiologists. In case of disagreement the final score was made by consensus.According to the literature, both the pubo-coccygeal line (PCL) and the HMO system (H line, M line and pelvic organ prolapse below the H line) were used in order to determine and assess the severity of pelvic floor weakness.Correlation between the extent of pubovisceral muscle avulsion and classification of pelvic floor weakness were performed using spearmn test. Statistical analysis were performed using SPSS for Windows (version19.0; SPSS Inc., Chicago, IL, USA).Results:All cases in pilot study completed the MR procedure successfully. The MR images were of enough clarity for evaluation. The measurements based on3.0-T MRI were reliable and repeatable. The ICCs for H line, M line and ano-rectal angle between two observer were0.88、0.93、0.81, respectively. The ICCs for two measurements of H line, M line and ano-rectal angle which performed by one radiologist were0.92、0.91、0.89, respectively.Two hundred thirty female cases (age range,34-84years; mean age,46.3years) were then enrolled in further study. The most common presenting clinical symptoms were constipation, incomplete evacuation, prolapse, incontinence, pelvic and rectal pain, bulge and rectocele, rectal ulcer and obstruction. Based on MR images cystocele, uterine prolapse, enterocele, rectal intussusception, rectal prolapse and rectocele were identified in38(16.5%),34(14.8%),3(1.3%),28(12.2%),0(0%) and108(46.9%) cases, respectively. For X-ray defecography, rectocele and rectal intussusception was identified in145(63.0%) and37(16.1%) cases, respectively.In comparison with X-ray defecography, thirty-seven rectoceles and9rectal intussusceptions were missed by MR images. Then the sensitivity and specificity of MRI vs. X-ray defecography were75.7%and100%respectively.Based on the pubovisceral muscle scores,85,102and43cases were categorized to normal, minor and major avulsion group. According to HMO grading system,7,121,89and4cases were scored as grade1, grade2, grade3and grade4, respectively. The extent of pubovisceral muscle avulsion significantly correlated with classification of pelvic floor weakness. The Spearman correlation coefficient was0.274.Conclusions:1. A one-stop MR procedure based on static and dynamic MR sequence for evaluation of female pelvic floor dysfunction was successfully established.2. The quantitative measurements based on dynamic3.0-T MRI sequence for female pelvic floor were reliable and repeatable.3. Morphological and functional abnormalities were clearly demonstrated on static and dynamic MR images; while the detection rates of rectocele and rectal intussusception on MRI was lower than those on X-ray defecography.4. Avulsion of pubovisceral muscle and pelvic floor relaxation could evaluated quantitatively and categorized on dynamic MR images combined with static images. The extent of pubovisceral muscle avulsion significantly correlated with classification of pelvic floor weakness. The avulsion of pubovisceral muscle may be the major risk factor for pelvic floor weakness, which may further cause pelvic floor dysfunction.