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Pelvic floor dysfunction, such as pelvic organ prolapse and urinary and fecal incontinence, impairs quality of life for a large number of women. The pelvic floor muscles (PFM) play a critical role in pelvic organ support[2, 3]. The pubovisceral muscle (PVM) is the most medial part of the levator ani complex bordering on the levator hiatus (LH). In recent years, three- and four-dimensional (3D/4D) transperineal ultrasound has become a useful diagnostic tool for visualizing the PVM, and has been shown to be reliable and valid[5-10]. However, while it has been suggested that it is easy to learn how to perform a 3D/4D transperineal ultrasound examination, a PubMed search did not reveal any studies investigating the learning process of both volume acquisition and analysis of the recorded volumes. Previous intra- and interobserver studies of 3D/4D transperineal ultrasound of the pelvic floor have shown acceptable reliability[5, 7, 8, 10], but to our knowledge these studies only tested reliability of the offline analysis. As far as we have been able to ascertain, there have been no studies investigating the reliability between two independent examiners for complete transperineal ultrasound examination including instructing the patient, and recording and analyzing the ultrasound volumes.
The primary aim of this study was to monitor the learning process for acquiring 3D/4D transperineal ultrasound volumes and for their offline analysis. A second aim was to perform an interobserver reliability study for the entire ultrasound procedure, including both volume acquisition and offline analysis.
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To our knowledge, this is the first study of the learning process for using 3D/4D transperineal ultrasound. We found that an examiner who had never performed a transperineal ultrasound examination was able to accomplish a volume acquisition with good to very good agreement with an experienced investigator after only 3 hours of learning. After the first 10 volume acquisitions, except for the pubic arc, the ICC values for LH dimensions at rest and during PFM contraction were excellent. On Valsalva, the ICCs for LH dimensions ranged between 0.79 and 0.87 and improved over the next 10 volume acquisitions to ICC ≥ 0.96. In our study no women were excluded because of incomplete scanning of the LH on Valsalva, which has been reported as a problem in previous studies[7, 16].
It was apparently easier for IE to instruct women to perform efficient PFM contractions than to perform proper Valsalva maneuvers, perhaps because all participants had already been taught how to perform a correct PFM contraction by a physiotherapist. In this study, Valsalva maneuver appeared more instructor-dependent. Valsalva can be confounded by co-contraction of the PFM, which results in lower LH diameter and area and is reported to be common in nulliparous women. Approximately 50% of our study population were nulliparous. It is imperative that the investigator is able to recognize potential co-contractions of the PFM as insufficient increase in anteroposterior diameter in the sagittal plane while recording in real time. Biofeedback, verbal instruction and repetition may help women to avoid co-activation during assessment of the Valsalva maneuver.
Learning the analysis procedure was more time-consuming: 20 hours were required to learn the offline analysis. After analysis of the first 10 ultrasound volumes, ICCs at rest, during PFM contraction and on Valsalva ranged widely, between 0.13 and 0.94. Agreement improved within the next 10 ultrasound volumes analyzed, with good to excellent reliability achieved for LHap, LHrl and LHarea during PFM contraction and at rest. These results are in accordance with findings in previous inter- and intraobserver studies testing the analysis process[5-8, 10, 17]. We also found excellent reliability for all LH dimensions on Valsalva after analysis of 20 volumes. Reported reliability for LHap and LHarea on Valsalva vary from excellent to moderate[7, 8, 12]. However, while others have reported good or excellent reliability for the pubic arc and LUG[12, 17], in contrast, we found the lowest reliability was achieved for these measurements, with ICCs of 0.40 and 0.70, respectively. Most investigators measure the pubic arc and LUG during PFM contraction when the insertion angle of the PVM into the pubic rami is most acute. Defining the insertion of the PVM can be difficult, especially postpartum. In the 10 women examined 6 weeks postpartum, the PVM displayed low contrast, and demarcation was challenging.
As far as we have been able to ascertain, this interobserver reliability study is the first study using two independent examiners performing the entire transperineal ultrasound procedure, both ultrasound volume acquisition and offline analysis. We found excellent reliability between the two observers for all LH measurements except for the pubic arc. Previous test–retest, intra- and interobserver studies of 3D/4D transperineal ultrasound have found acceptable reliability for measurements of LH dimensions[5-8, 10]. In all these studies, ultrasonography was performed by the same examiner. We did not find any studies evaluating reliability for volume acquisition with transperineal ultrasound between two different examiners. Weinstein et al. performed an intra- and interobserver reliability study of PFM morphology, in which two independent examiners performed volume acquisition and offline analyses using a transvaginal probe, and found good to very good reliability for LHap and LHarea during PFM contraction and at rest. The limits of agreement in our study are comparable to those of the interobserver study of Majida et al..
A limitation of our study is that only one inexperienced examiner was included. Our main aim was to introduce a new co-worker into an already established team as quickly as possible, ascertaining good-quality ultrasound data with minimal variation. The generalizability of our findings might be questioned, not only because of the limited number of inexperienced examiners, but also because of the patient characteristics. For example, in a group of patients with pelvic organ prolapse, transperineal ultrasonography might be more difficult to accomplish owing to the larger LH area on Valsalva and to the limited acquisition angle of the transducer. Yet, 50% of our study women were examined 6 weeks postpartum, when anatomical structures display low contrast. Regarding sample size, the number of women included was in line with other published reliability and validation studies in this area[5, 6, 9]. Although better ICC values for LUG and pubic arc might have been achieved by including more women, IE had already accomplished the ultrasound examination and offline analysis with good and very good agreement with E for the other measurements after 20 examinations, indicating that measurements of LUG and pubic arc were more difficult to assess.
To include 3D/4D transperineal ultrasound in a routine gynecological examination of women with pelvic floor disorders, the technique has to fulfill at least two criteria. First and most importantly, information from a transperineal ultrasound examination should give clinically useful information. To date, information about the PVM has been found to be helpful in selecting patients with high risk of prolapse recurrence. Second, the examination should be easy to perform and the imaging reliable and easy to interpret. In this study we have confirmed that 3D/4D transperineal ultrasound can be learned with an acceptable level of effort. The excellent ICC values of the interobserver study show that it is a reliable tool for examining the PVM.
In conclusion, 3D/4D transperineal ultrasound is a reliable technique that can be learned in a short period of time and could be incorporated easily into examinations of the pelvic floor, in the same way in which ultrasound of the uterus and adnexa is included in routine gynecological examinations today.