All EVUS images in this chapter are obtained from a BK Flex Focus medical scanner (Fig. 6.2) (BK Ultrasound, Analogic, Peabody, MA, USA). For obtaining optimal images, we recommend that the operator has a clear understanding of the technique, as well as familiarity with the controls of the machine. Most importantly, improper settings of the equipment can lead to artifact, leading to unreliable ultrasound results.

Two 360° probes can be used for endovaginal levator ani imaging. The BK 2052 transducer (Fig. 6.3) has a built-in 3D automatic motorized system (proximal-distal actuation mechanism is enclosed within the shield of the probe). This equipment allows for the acquisition of 300 images in 60 s for a distance of 60 mm. The BK 8838 probe is a 60 mm 360° rotational transducer and obtains an image every 0.55° for a total of 720 images (Fig. 6.4), providing more detailed information. The images are acquired automatically with the touch of the 3D button on the equipment console. The data from the closely spaced 2D images are combined as a 3D volume displayed as a data volume that can then be stored and analyzed separately.

No special patient preparation is required and no vaginal or rectal contrast is necessary. The patient is asked to keep a comfortable amount of urine in the bladder. The patient is placed in the dorsal lithotomy position and the probe is inserted in a neutral position, with care not to press on the upper or lower vaginal areas so as not to distort anatomy. The probe should create a horizontal line with the body’s axis. When placing the ultrasound gel in the probe cover, we recommend that air bubbles be gently squeezed out of the probe cover to minimize the potential for artifact.

Once 3D endovaginal imaging is selected on the console, the rotating crystal will begin to rotate, signaling that the probe is ready for insertion. The probe is inserted as described in Chap. 2. Based on our anatomic studies, we recommend placing the probe 6 cm inside the vagina, just 2 cm above the level of the urethrovesical junction. If using the 2052 probe, the two buttons that move the crystal cephalad and caudad should be facing the 12 o’clock position. Once the acquisition is started, it is important that the operator minimizes movement by stabilizing the probe during the full length of the scan. This will help optimize image quality in obtaining the 3D volume.

Previous research has shown that images obtained on EVUS of the pelvic floor muscles have good to very good correlation with the muscle parts in cadaveric sections [7]. A standardized approach of obtaining EVUS images of the pelvic floor has been described [8] and evaluated [9] (Fig. 6.5). The evaluation of this standardized approach in nulligravid women revealed a good to very good interobserver and interdisciplinary reliability; Cohen’s kappa = 1 for LAM attachment to the pubic bone and Cronbach’s α = 0.970 for levator hiatus anteroposterior length, width, and area [10]. To assess the reliability of LAM biometry and avulsion, a sample of parous women were analyzed [10]. The same standardized approach was used as previously described, and intra- and interobserver analyses were performed. The study compromised 169 pregnant women at around 36 weeks of pregnancy, 83 women within a few days following delivery, and 75 women 3 months postpartum.

Intraobserver reliability was excellent for hiatal measurements (Table 6.1, Fig. 6.6). Interobserver analysis of antenatal measurements revealed excellent reliability for hiatal area (intraclass correlation coefficient, ICC 0.86) and hiatal anteroposterior diameter (ICC 0.80) (Table 6.2). Similar results were found in the analysis of volumes that had been acquired early postpartum (Table 6.3) and 3 months postpartum (Table 6.4). Limits of agreement were analyzed not only to assess correlation, but also to assess whether the measurements were around the same value. Close agreement between observers was found, emphasizing the reliability of these measurements [11].

Intraobserver analysis was excellent (ICC 1.00) for avulsion of the pubococcygeus part of the LAM, and excellent (ICC 0.79–1.00) for the puborectalis part. The interobserver analysis was excellent (ICC 0.97–1.00) for avulsion of the pubococcygeus part of the LAM and excellent (ICC 1.00) for the puborectalis part [11].

Recent literature has identified the distal subdivisions of the levator ani, classifying them based on attachment points, using magnetic resonance imaging (MRI). By MRI the LAM has been divided into pubovisceralis (to include pubovaginalis, puboanalis, puboperinealis, pubococcygeus, and iliococcygeus) and puborectalis [12]. Morgan et al. have described levator ani defects and scored unilateral muscle defects separately [13]. The terminology for EVUS is different, and in order to better functionally describe these LAM subdivisions, we group them as the puboanalis, puborectalis, and pubovisceralis (Chap. 5). Our technique and the anatomical descriptions were first authenticated in female cadavers and then in live human female volunteers, documenting superior, dynamic imaging, and visualization of these structures [7]. LAM injury has been described on MRI studies as a “defect” or “avulsion,” attributed to causes such as obstetric factors, aging, or hormonal changes.

The pelvic floor muscles have the unique role of supporting the urogenital organs and the anorectum. Unlike most other skeletal muscles, the LAM maintains constant tone, except during voiding, defecation, and Valsalva maneuver. At rest, the LAM keeps the urogenital hiatus closed by compressing the vagina, urethra, and rectum against the pubic bone, and maintains the pelvic floor and pelvic organs in a cephalic direction [1]. Pelvic floor muscles are integral to pelvic organ support, and while functioning properly, provide support to the pelvic organs, keeping the ligament and fascial attachments tension-free.

During parturition , the LAM stretches beyond its limits [14, 15] in order to allow passage of a term infant. Studies have shown that LAM injury occurs in 13–36% of women who deliver vaginally [16, 17]. There are various definitions of levator ani injury, according to the mode of assessment and imaging modality. Most authors have used avulsion of the muscles as the end point of the study. However, more recent publications using 3D EVUS have found that up to 35% of women may have hematoma formation after their first delivery (Fig. 6.7). Assessment of the levator muscles is essential for a complete understanding of pelvic floor anatomy abnormalities, as well as of pelvic floor dysfunction.

It has been accepted that obstetric trauma is the main etiological factor in the development of LAM avulsion. As stated in the introduction, trauma can occur by stretching of the inner part of the LAM (namely, the pubococcygeus part of the muscle), and by disconnection of its insertion from the inferior pubic ramus and the pelvic side wall [1]. A recent review found a 13–36% incidence of LAM avulsion following the first vaginal delivery [5]. Overall, the highest incidence (39.5%) was found in a prospective study where women were seen in the early postpartum period, using transperineal ultrasound. The authors attributed this higher incidence to the difficulty in differentiating fluid collections from LAM avulsion [18]. In our opinion, they used transperineal ultrasound, which is less discriminatory for the different parts of the LAM. Another more recent study evaluated the LAM shortly after childbirth using EVUS in a prospective study [6]. A total of 114 women underwent EVUS early postpartum. In 27 women (23.7%) the investigators found well-delineated, hypoechoic areas consistent with hematomas (Fig. 6.8). Importantly, there was 100% agreement between the investigators for the presence of a hematoma. Hematomas away from the LAM attachment zone to the pubic bone resolved. Hematomas that were found at the area of attachment of the pubococcygeus part of the LAM to the pubic bone manifested as pubococcygeus avulsions 3 months postpartum. Hematomas were significantly associated with episiotomy, instrumental delivery, and increased hiatal measurements. Palpation of LAM avulsion, according to a previously described protocol [19], was unreliable early postpartum, as only seven avulsions were diagnosed using the finger as an instrument.

In an additional, smaller, group of women, the investigators did not find hematomas but avulsion of the pubococcygeus part of the LAM in the early postpartum period. The overall incidence of LAM avulsion was 12.0% 3 months postpartum. The authors therefore concluded that hematomas in the pubococcygeus part of LAM, where it is supposed to be attached to the pubic bone, always result in avulsion diagnosed 3 months postpartum. On the other hand, one third of avulsions confirmed at 3 months postpartum are not preceded by a hematoma at the site of LAM attachment to the pubic bone, but could be seen as an avulsion in the early postpartum period [6]. The authors speculated that a hematoma is formed when muscle is torn away from the tendinous attachment. However, no hematoma is formed when the tendon or pubovisceral enthesis is avulsed from the pubic bone, due to the avascular nature of the trauma [20]. The resolution of hematomas at or away from the attachment zone of LAM to the pubic bone directs to the body’s ability to heal itself [21].