Further Investigations and Follow-Up: Pelvic Floor Ultrasound

Fig. 10.1

A GE probe applied transperineally to obtain 3D/4D data volumes

Fig. 10.2

Tomographic ultrasound images obtained using transperineal ultrasound of (a) a typical intact levator ani muscle (LAM) in a nulliparous woman and (b) a bilateral LAM avulsion in a multiparous woman. Slices were obtained at 2.5-mm intervals below and above the level of minimal hiatal dimension (*). LAM defects are indicated in (b) by * (Reprinted from Schwertner-Tiepelmann et al. [63]; with permission from John Wiley and Sons

Fig. 10.3

Three-dimensional rendered volumes obtained on transperineal ultrasound showing: (a) an intact levator ani muscle (LAM) displayed in an oblique axial plane in a nulliparous woman and (b) a bilateral avulsion injury. LAM defects are indicated in (b) by (*). IR inferior ramus os pubis, L levator ani muscle, R rectum, U urethra, V vagina (Reprinted from Schwertner-Tiepelmann et al. [63]; with permission from John Wiley and Sons)

The description of the levator ani muscle subdivisions by 3D endovaginal ultrasonography (EVUS) was reported in 2008 and published in 2009 [21]. EVUS methodology and description of muscles was authenticated in a systematic manner. First the anatomic correlation [21] and subsequently histologic correlations were made in nulliparous women [22]. Interrater and interdisciplinary reliability of EVUS were subsequently described in nullipara [23]. Interrater reliability assessments of these measurements during pregnancy and postpartum have been performed.

Compared with other imaging modalities, ultrasound imaging is widely available, easy to perform, and familiar to many medical specialties. These advantages have made it feasible for many researchers to study early postpartum pelvic floor injuries and structural changes and further correlate them with obstetric factors.

Levator Ani Muscle Trauma

During vaginal delivery, overstretching of levator ani muscle can predispose muscle to disconnect from its insertion on the inferior pubic ramus and pelvic side wall. Based on studies using 3D/4D pelvic floor ultrasound, the prevalence of levator ani muscle trauma after vaginal delivery is 13–40 % [14, 24, 25]. In a study of 114 postpartum women with EVUS, one third of primiparous women delivering vaginally developed levator ani muscle hematomas within hours of delivery diagnosed using high frequency EVUS. When hematoma was located in the attachment zone of the levator ani muscle to the pubic bone, levator ani muscle detachment from the pubic symphysis was almost always identified three months postpartum. When hematoma was located away from the attachment zone, a defect was most often not seen three months postpartum [26]. The mode of delivery has an impact on levator ani muscle injury. In a study on 157 postpartum women, the risk of levator defect after vaginal delivery was more than seven times higher than after cesarean section [27]. Instrumental delivery by forceps was one the most important risk factors as levator injury was detected in 60–64 % of women who had been delivered by forceps [28, 29]. Another study reported a prevalence of 18 % of levator lesions among women who had a non-instrumental vaginal delivery, 14 % among women who delivered by vacuum and 40 % among women who delivered by forceps, but reported no levator lesions in the cesarean delivery group [30]. Chan et al. showed similar findings in Chinese women after first vaginal delivery. The rate of muscle injury for spontaneous vaginal delivery, ventouse extraction and forceps delivery were 15.4 %, 33.3 %, and 71.4 %, respectively. There was no levator muscle injury in cesarean section groups [31].

EVUS Technique for Visualization of Levator Ani Muscle

3D endovaginal ultrasound can give us high-quality images of levator ani muscle subdivisions. It is not known if the EVUS can detect LA subdivisions better than MRI. Imaging is obtained using the BK Medical Flexfocus (Peabody, MA, USA) and a 2052/8838 transducer (Fig. 10.4). All ultrasound scans are performed in the office setting, with the patient in dorsal lithotomy position, with hips flexed and abducted. No preparation is required and the patient is recommended to have a comfortable volume of urine in the bladder. No rectal or vaginal contrast is used. To avoid excessive pressure on surrounding structures that might distort the anatomy, the probe is inserted into the vagina in a neutral position. It has been shown that endovaginal probe does not have any adverse effect on anatomy comparing to transperineal ultrasound [32]. Three hundred axial images over a distance of 6 cm are taken in 60 s; 360° EVUS volumes are digitally stored for further analysis.

Fig. 10.4

A BK probe applied endovaginally to obtain 3D volume

The approach to 3-dimensional endovaginal ultrasound takes into account certain, easily recognizable anatomic landmarks [21]. We delineated three ascending levels with level 1 being the most caudal and level 3 the most cephalad (Fig. 10.5). This categorization was utilized for interrater reliability validation. Level 1 contained muscles that insert into the perineal body, namely the superficial transverse perinei, puboperinealis and puboanalis. The superficial transverse perinei served as a reference point (Fig. 10.6a, b). Level 2 contained the attachment of the pubovaginalis, puboperinealis, puboanalis and puborectalis, and iliococcygeus to the pubic bone (see Fig. 10.6c–f). Level 3 contained subdivisions visible cephalad to the inferior pubic ramus, namely the pubococcygeus and iliococcygeus, which winged out toward the ischial spine (see Fig. 10.6g–j). This standardized approach of endovaginal ultrasound assessment of levator ani muscle subdivisions has been verified with good to excellent interobserver and interdisciplinary reliability, with kappa values of 0.6–1 [21].

Fig. 10.5

The relative position of levator ani subdivisions during ultrasound imaging. Levels 1–3 are identified below the figure. The A-J markings on top of the figure correspond to the ultrasound images shown in Fig. 10.4. IC iliococcygeus, PP puboperinealis, STP superficial transverse perinea, PA puboanalis (Reprinted with permission from Shobeiri et al. [21])

Fig. 10.6

Levator ani subdivisions seen at different levels. Midline structures are identified in lateral views with corresponding colors in the picture inserts at the upper left corner of the ultrasound images at each level. The green vertical line in the insert corresponds to the relative position in the vagina where the image was obtained. (a) Level 1A. At 0 cm, the first muscle seen is the superficial transverse perinei (green) with mixed echogenicity. (b) Level 1B. Immediately cephalad to the superficial transverse perinei is the puboperinealis (yellow), which can be traced to PB with manipulation of the three-dimensional cube. It comes in at a 45° angle as a mixed echoic band to join the perineal body. Lateral to it, the puboanalis is seen as a hypoechoic triangle (pink). (c) Level 2A marks the attachment of the muscles to the pubic arch. The external urethral meatus is visible (dark red). Puboperinealis and puboanalis insertions are highlighted. (d) Level 2B. Pubovaginalis (blue) and puborectalis (mustard) insertions come into view. The urethra and the bladder are outlined (red) in the lateral view. (e) Level 2C. The heart-shaped vaginal sulcus (outlined in red) marks the pubovaginalis insertion. Iliococcygeus fibers (red) come into view. The perineal body is outlined in the lateral view. (f) Level 2D. The puboanalis is starting to thin out. The puborectalis is seen in the lateral view. (g) Level 3A. The puboperinealis and puboanalis become obscure. Anatomically, the puboanalis becomes a thick, fibromuscular layer forming a tendineus sheet-the rectal pillar (RP). The perivesical venous plexus is prominent (purple). The rectovaginal fibromuscularis is shown (green) in the sagittal view as a continuous, mixed, echogenic structure approaching the perineal body and laterally attaching to the RP. (h) Level 3B. The RP (orange) is seen easily. The iliococcygeus becomes prominent and widens. (i) Level 3C. The iliococcygeus widens further and inserts into the arcus tendineus fascia pelvis. (j) Level 3D. The puborectalis and iliococcygeus fade out of view. The puborectalis (mustard) and iliococcygeus (red) are outlined in the lateral view, showing their entire course (Reprinted with permission from Shobeiri et al. [21])

Levator Ani Deficiency

The majority of patients with pelvic floor disorders remote from delivery did not have evidence of birth-related injury at the level of the pubic symphysis, rather they had global atrophy and deficiency of the muscle. Based on functional anatomy of subdivisions of the levator ani muscle a scoring system for evaluation the severity of levator ani deficiency (LAD) was described for EVUS [33]. By EVUS, levator ani muscle subdivisions were evaluated in their specific axial plane where the full length of muscle could have been visualized and were scored (0 = no defect, 1 = minimal defect with <50 % muscle loss, 2 = major defect with >50 % muscle loss, 3 = total absence of the muscle) on each side based on thickness and detachment from the pubic bone as previously used in the MRI studies [34]. Each muscle pair score ranged from 0, indicating no defects, to maximum score of 6, indicating total muscle absence. For the entire levator ani muscle group, a cumulative levator ani deficiency (LAD) score that ranged between 0 and 18 was possible [33] (Fig. 10.7a–c). Although patients with normal support can have severe LAD, no patient with advanced prolapse demonstrates normal musculature.

Fig. 10.7

(a) The axial view of pelvic floor muscles with no LA muscle deficiency. A anus, LA levator ani, PA puboperinealis/puboanalis, PR puborectalis, PS pubic symphysis, PV pubovisceralis, V vagina. * denotes a missing muscle. Numbers are muscle scores. (b) The axial view of pelvic floor muscles with moderate LA muscle deficiency. * denotes a missing muscle and numbers are muscle scores. A anus, LA levator ani, PA puboperinealis/puboanalis, PR puborectalis, PS pubic symphysis, PV pubovisceralis, V vagina.* denotes a missing muscle. Numbers are muscle scores. (c) The axial view of pelvic floor muscles with severe LA muscle deficiency. * denotes a missing muscle and numbers are muscle scores. A anus, LA levator ani, PA puboperinealis/puboanalis, PR puborectalis, PS pubic symphysis, PV pubovisceralis, V vagina. * denotes a missing muscle. Numbers are muscle scores (Reprinted with permission from Rostaminia et al. [33])

Pelvic Floor Biometry

One of more recent applications of cross-sectional imaging of the female pelvic floor is pelvic floor biometry. Minimal levator hiatus dimensions, levator plate mobility, bladder neck mobility, urethral sphincter volume, anorectal angle, and pelvic organ mobility are the most common measurements that have been used in this area [20, 30, 35–38]. Researchers work on structural changes of the pelvic floor by using these measurements and try to find associations between these changes and pelvic floor dysfunction symptoms as they believe distorted anatomy can lead to malfunction.

3D ultrasound has made it feasible to visualize morphological changes of the pelvic floor after delivery. Levator hiatus distensibility, urethral sphincter volume and bladder neck mobility were assessed using ultrasound imaging in pregnancy, 6 weeks and 6 months after delivery in 156 women. It was shown that vaginal delivery is strongly associated with a larger, more distensible levator hiatus and a greater degree of bladder neck mobility both antenatally and postnatally [39]. Using 3D perineal ultrasound in 130 primiparous on second day postpartum, women with vaginal or operative vaginal delivery had a significantly larger hiatal area and transverse diameter than women who delivered by caesarean section [40]. Shek et al. have shown that both hiatal dimensions and urethral mobility were markedly higher in late pregnancy and at 4 months after labour compared to nulliparous controls [41]. It was also shown that vaginal childbirth results in enlargement of the levator hiatus, especially after an avulsion. However, even without major levator trauma, there may be increased distensibility of the hiatus, which may be another mechanism leading to enlargement of the hiatus and pelvic organ prolapse [30]. Using 3-4D TPUS, levator hiatal area was significantly higher after forceps delivery [29]. Perineal body and anorectal junction mobility can be assessed by 3D pelvic floor ultrasound and it was shown than vaginal delivery increased the mobility of the perineal body and the anorectal junction [42].

3D EVUS Technique for Pelvic Floor Biometry

EVUS has been reliably used for pelvic floor biometry values such as minimal levator hiatus (MLH) and anorectal angle (ARA) with good to excellent interobserver and intradisciplinary reliability, with kappa values of 0.6–0.9 [23, 43].

Minimal Levator Hiatus Dimensions and Area

3D EVUS volumes obtained by 360° endovaginal probe has been used for this measurement. The mid-sagittal plane is used to identify the minimal distance between hyperechoic posterior aspect of the symphysis pubis and the hyperechogenic anterior border of the levator plate (Fig. 10.8). The shortest line between the levator plate and pubic symphysis corresponding to the anterior-posterior line or height of the minimal levator hiatus is drawn (Fig. 10.9). Ultrasound volume can be tilted and axial plane at the level of this line is used for minimal levator hiatus dimensions measurements (Fig. 10.10).

Fig. 10.8

Anorectal angle in mid-sagittal view by transvaginal 360° ultrasound. Anal axis (AA) and the rectal axis (RA) lines form the anorectal angle. A anterior, B bladder, C caudad, LP levator plate, PS pubic symphysis, U urethra, V vagina (Reprinted with permission from Shobeiri et al. [20])

Fig. 10.9

Levator plate descent angle in mid-sagittal view by transvaginal 360° ultrasound. A anterior, AP antero-posterior line of minimal levator hiatus (blue line), B bladder, C caudad, LP levator plate, LPDA levator plate descent angle, PLURAL Pubic Levator Ultrasound Reference Assessment Line (green line), PS pubic symphysis, U urethra, V vagina (Reprinted with permission from Shobeiri et al. [20])

Fig. 10.10

Minimal levator hiatus area in axial plane by transvaginal 360° ultrasound. AP line is in blue. Puborectalis pubococcygeus border is delineated with small arrows. A anterior, AP antero-posterior line of minimal levator hiatus (blue line), LR left-right axis of minimal levator hiatus, PC pubococcygeus, PR puborectalis, PS pubic symphysis, U urethra, V vagina (Reprinted with permission from Shobeiri et al. [20])

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