Dynamic transvaginal ultrasound examination for assessing anatomy of parametrium

During a recent international multidisciplinary meeting (Marathon for Solidarity, November 2022; https://roma.unicatt.it/evt-ultrasound-of-pelvic-anatomy-marathon-for-solidarity), we discussed the methodology to assess the parametrium on ultrasound examination as we realized that there is no consensus on this issue. Transvaginal ultrasound examination is the method of choice for assessing the extent of disease in cervical cancer1 and endometriosis2. However, few authors have described the methodology for the anatomical assessment of the parametrium on ultrasound, tending to focus instead on evaluation of the uterosacral (or sacrouterine) ligaments3, 4. In this article and Videoclip S1, we describe, following multidisciplinary meetings at our institution, how to assess the structures surrounding the cervix and vagina (namely the parametrium), ventrally, laterally and dorsally, on transvaginal ultrasound in a healthy menstruating-age patient. We describe the structures composing the parametrium (i.e. septa, ligaments and paracervix) at the level of the vagina and cervix. Spaces (i.e. paravaginal and pararectal spaces) are not reported, as they are not assessable on ultrasound. To assess the parametrium, no particular patient preparation is required except for a minimal amount of fluid in the bladder. Typically, the transvaginal probe is positioned in the anterior fornix or in the posterior vaginal fornix in cases of anteverted or retroverted uterus, respectively. Ventrally, the vesicovaginal septum is comprised of areolar tissue joining the bladder to the vagina, and the vesicovaginal ligaments (connective tissue caudally adjacent to the terminal part of the ureters) form the lateral limit of the vesicovaginal septum. On ultrasound, the vesicovaginal septum can be assessed in a midsagittal section by pushing the uterus and vagina against the bladder, the vesicovaginal ligaments appearing as hyperechogenic tissue. Laterally, using the ureter as an anatomical marker, the ureter divides the lateral attachments of the uterus to the pelvic wall into the paracervix/paracolpium containing the vaginal artery and vein and the parauterine lymphovascular tissue (named ‘parametrium’ in Terminologia Anatomica) containing the uterine artery and superficial uterine vein5. On ultrasound, the paracervix/paracolpium and parauterine lymphovascular tissue correspond to the area between the cervix and the pelvic wall with the ureter located in the central part of this area, dividing it into medial and lateral components. Dorsally, the rectovaginal septum is composed of areolar tissue joining the rectum to the vagina in the midline and the rectovaginal ligaments correspond to the lateral limits of the rectovaginal septum. On ultrasound, the rectovaginal septum can be assessed in a midsagittal section by pushing the probe against the rectum and vagina. The rectovaginal ligaments correspond to the hyperechogenic strips between the posterior vaginal wall and anterior wall of the rectum. Ventrally, the bladder pillars, which are highly complex structures, variably encompass the vesicouterine ligaments (connective tissue crossing over the terminal part of the ureters, located cranial to the ureters) and the lateral vesical ligaments. The bladder pillars contain the obliterated umbilical artery, the superior vesical artery, the vesical veins and the autonomic bladder nerves. The vesicouterine ligaments are in continuum with the vesicovaginal ligaments described above. On ultrasound, the ligaments appear as echogenic tissue surrounding the terminal part of the ureter (cranial to the ureter). The vesicouterine septum can be assessed by pushing the uterus against the bladder. Laterally, the anatomical aspects and assessment on ultrasound are as described for structures surrounding the vagina. Dorsally, the uterosacral (or sacrouterine) ligaments are folds of the peritoneum in the pouch of Douglas. Caudally, they are in continuum with rectovaginal ligaments and hypogastric nerves5. On ultrasound, they appear as hyperechogenic tissue surrounding the cervix, which can be assessed in both sagittal and transverse sections. The transvaginal probe should be positioned either in the anterior fornix or in the posterior/lateral fornix to visualize the tissue stretched by the pressure of the probe, as suggested by Leonardi et al.4. In conclusion, the parametrium, i.e. structures surrounding the cervix and vagina, can be assessed and defined on transvaginal ultrasound examination. Further multicenter meetings will be needed to reach an international consensus on the optimal methodology for this. We thank Dr Susan Dababou, MD, from the Department of Obstetrics and Gynecology, AOUI Verona, University of Verona, Italy, and Mr Emerson Marinho Pinto, Dipartimento Scienze della Salute della Donna, del Bambino e di Sanità Pubblica, Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Rome, Italy, for production of the video. Data available on request from the authors We start by inserting the probe into the vaginal introitus. On the right of the screen, we can identify the urethra and the bladder with some fluid; in the center is the vaginal wall and on the left the rectum. Then, we gently advance the probe to the anterior vaginal fornix and we can visualize the cervix, in a sagittal section. We identify here the anterior and posterior lips of the cervix, and the internal and external uterine ora. Moving the probe cranially, we can visualize the uterus and the endometrium. The vesicovaginal septum can be evaluated by pushing the vagina and uterus against the bladder. Then, moving the probe from the mid- sagittal section to the lateral sagittal section we can visualize the terminal part of the ureter next to the bladder and assess the hyperechoic tissue surrounding the terminal part of the ureter corresponding to vesicovaginal (caudal to the ureter) and vesicouterine (cranial to the ureter) ligaments. We can repeat the procedure on the other side to visualize the contralateral structures. Subsequently, moving the probe laterally, we can visualize the ureter and the crossing point of the uterine vessels, then we can rotate the probe 90° at the level of the crossing point: in this transverse section we can visualize the cervix, vagina, ureter and pelvic wall. The region between cervix and pelvic wall (with the ureter in the middle) corresponds to the paracervix/paracolpium and parauterine lymphovascular tissue. To assess the dorsal compartment, we return the probe to the anterior vaginal fornix. From a mid-sagittal section of the cervix, we can recognize the vaginal wall, the vagina fornix, the uterine torus, and the retrocervix. Then, in a sagittal section, we can slowly lateralize the probe to assess the posterior hyperechoic tissue surrounding the cervix (corresponding to the “uterosacral or sacrouterine ligament”). We can then repeat the same movements on the other side, to assess the same structures. Finally, we sweep the probe 90° clockwise and, by moving the probe craniocaudally, we can assess the “uterosacral or sacrouterine ligaments” and more caudally, the rectovaginal ligaments in a transverse plan. The “uterosacral or sacrouterine ligament” can be also assessed positioning the probe in the posterior vaginal fornix, exerting pressure against the hyperechoic tissue in a semihorizontal direction. Finally, in the midsagittal section we can visualize the rectovaginal septum by pushing the probe against the rectum and vagina. 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