For more details about this, refer to Chap. 3, “Instrumentation and Techniques for Perineal and Introital Pelvic Floor Ultrasound.”

The ability of 3D pPFUS to produce high-resolution images of the pelvic floor in 3 planes has rendered it a valuable tool in studying pelvic floor disorders stemming from childbirth injury. Although vaginal birth has long been linked with pelvic organ prolapse and urinary and fecal incontinence [10–12], recent advances in ultrasound and MRI have enabled researchers to identify the underlying pelvic floor injuries. Dietz et al. have reported levator ani muscle injury (avulsion) in 15–30% of parous women with one or more vaginal deliveries [13, 14]. Similar findings were reported by use of MRI [12]. Levator ani injuries can be depicted on 3D pPFUS/translabial ultrasound in the axial plane or the rendered volume, which is reproduced automatically by synthesis of the sagittal, coronal, and axial planes. For this, the plane of minimal hiatal dimensions is identified in the midsagittal view, as the shortest distance between the inferior most aspects of the symphysis pubis to the anorectal angle, marked by the levator plate [15]. In order for best views to be achieved on this plane, a step-by-step standardized rotation technique is described below:

In this plane, measurement of the hiatal dimensions can be taken: anteroposterior and transverse diameter, as well as hiatal area, either at rest, muscle contraction or at Valsalva (Fig. 4.9). In addition avulsion injuries can be depicted by reference to this plane, however data suggest that these injuries are best demonstrated at pelvic floor contraction and particularly so on Tomographic Ultrasound Imaging (TUI) mode in order to appreciate the extent of injury (partial injury or complete avulsion) [16]. Fig. 4.10 shows a levator muscle injury (LAM) avulsion in a parous woman, while levator hiatal overdistension can be appreciated in Fig. 4.11.

Levator ani muscle injury has been proposed as one of the potential causes for pelvic organ prolapse and to a lesser degree stress urinary incontinence [13, 14]. Studies on MRI of the pelvic floor have looked into grading LAM injuries and suggested an association with prolapse [16], however no universal agreement exists so far on a classification system for such defects [17]. This becomes highly relevant when considering data that suggest that the origin of the LAM from the pubic bone may not be visible bilaterally in up to 10% nulliparous women, alluding to inherent limitations in 3D ultrasonography or/and anatomical variations in the LAM morphology [18].

Several risk factors, associated with childbirth, have been identified for LAM injury; forceps delivery incurs an odds ratio (OR) of up to 14.7, protracted second stage of labor an OR of 2.27, while vacuum delivery does not seem to constitute a risk factor [19, 20]. In turn, LAM injury, as a result of vaginal delivery, has been shown to correlate with prolapse in the anterior and midvaginal compartments, but not with rectocoele or stress urinary incontinence [14]. LAM defects are also a strong predisposing factor for recurrent prolapse in women with previous surgical repair [21].

One of the very first applications of 2D perineal/introital ultrasound of the pelvic floor was the assessment of bladder neck position in women with stress urinary incontinence. In 1995 Schaer et al. [3]. described a coordinate system for bladder neck and urethral mobility ultrasound appearance; x-axis is determined by a straight line through the central portion of the pubic symphysis, while a line perpendicular to that at the lower level of the pubic symphysis represents the y-axis. The urethrovesical angle or the UVJ is measured by creating a perpendicular line from the x-axis on the image, and following this line to the margin of the bladder base when the patient is at rest. The most common index in assessment of bladder neck position and urethral mobility are the urethral height (H), which is defined as the distance between the lower edge of the pubic symphysis and the bladder neck [22] (Fig. 4.12). In continent women normal values measured for urethrovesical angle is 96.8° at rest and 108.1° with Valsalva maneuver, and for height are 20.6 and 14.0 mm, respectively [22].

Another index that can be studied with pPFUS in regard to the bladder neck is the posterior urethrovesical angle. This is the angle between the urethral axis and the bladder floor and can be measured at rest, at maximum contraction or maximum Valsalva (Fig. 4.13).

Previous studies have shown high reproducibility of the ultrasound measurement of bladder neck descent [23]. Although there is no definition of normality regarding bladder neck descent, cut-offs between 15–40 mm have been proposed to define hypermobility. Various confounders such as bladder volume, patient’s position, and catheterization have been shown to influence measurements. Interestingly, mobility appears to be greater when the bladder is empty, whereas better imaging of BN funneling is observed when the bladder is full [24]. It is also worth noting that executing, and more so standardizing, an effective Valsalva maneuver can often be difficult, especially in nulliparous women who frequently co-activate the levator muscle [25].

Bladder neck descent has both a congenital and an environmental etiology, the latter being mainly linked with direct birth trauma and prolonged second stage of labor [26, 27]. Perineal ultrasound imaging of the bladder neck with a standard Valsalva pressure of 40 cm H2O has been used as a method of predicting the development of stress urinary incontinence postnatally; a woman in the third trimester with a bladder neck movement of greater than 1 cm or 40° has a 50% chance of persisting postnatal stress incontinence. If the bladder neck movement is less than this, then the risk of postnatal stress incontinence is 5% [28]. Antenatal pelvic floor exercises can halve the incidence of postnatal stress incontinence in the high risk group [29]. Correlation between ultrasound findings of bladder neck descent measurements and urodynamic testing has been inconsistent [30, 31] and largely does not help distinguish continent and incontinent women [32].

Another easily visualized feature of the urethrovesical junction is urethral funneling [33]; widening of urethral meatus may be observed on Valsalva, and sometimes even at rest, and is often, but not always, associated with urine leakage.

3D ultrasound scanning of the pelvic floor can also clearly depict the urethral sphincter, offering a useful tool for investigating both urethral anatomy and function [34, 35]. This technique had been previously validated by correlating urethral images from cadavers with histological findings [36]. Athanasiou et al. have demonstrated that women with stress urinary incontinence have smaller urethral sphincter volumes, as well as shorter and thinner urethras than their continent counterparts [37]. A recent study showed that 3D pPFUS is reliable in measuring urethral sphincter volume in nulliparous asymptomatic women [38]. The technique, which involves volume calculation on 1-mm cross-sectional areas at set distances across the urethra rather than the use of standardized mathematical equations, is demonstrated in Fig. 4.14.

By use of this technique researchers have demonstrated that black nulliparous premenopausal asymptomatic women have a larger urethral rhabdosphincter than their Caucasian counterparts, perhaps partially explaining the racial differences in the prevalence of stress urinary incontinence [39, 40]. Although the clinical benefit of measuring urethral sphincter volume in patients with urinary incontinence is so far unsubstantiated, the value of perineal ultrasound as an adjunct in guiding women with stress urinary incontinence through pelvic floor muscle training has been demonstrated [41, 42].

2D perineal ultrasound has been utilized as a diagnostic adjunct for overactive bladder and detrusor overactivity. Increased bladder wall thickness (BWT) (proposed cut-off is 5 mm) has been described in patients with overactive bladder (OAB) or detrusor overactivity and is hypothesized to be associated with detrusor hypertrophy secondary to isometric contractions [43, 44]. Recent systematic reviews have looked at different techniques of BWT measurement and suggested that discrepancies between the described techniques do not allow for safe conclusions about its diagnostic accuracy to be drawn (Fig. 4.15) [45].

The advent of 3D/4D technology in perineal/translabial ultrasound has popularized the modality as an aid to the clinical evaluation of uterovaginal prolapse. One of the first papers by Dietz et al. described a quantification method for POP by use of pPFUS and reported good correlation with clinical staging of prolapse by pelvic organ prolapse quantification system (POPQ), more so in the anterior and midvaginal compartment [46]. Lone et al. explored the relationship between 2D perineal ultrasound and POPQ system in staging prolapse and concluded that the accuracy of pelvic floor ultrasound in quantifying prolapse is limited [47]. Occasionally, a clinical finding of anterior wall prolapse may form a false impression of cystocele, while the bulging the tissue is in fact a urethral diverticulum or an anterior enterocele. pPFUS of the pelvic floor can be helpful in enhancing the diagnosis and thus dictate the appropriate management (Fig. 4.16).

Ultrasound imaging of the posterior compartment is characterized by good agreement between the degree of rectocele on examination and the rate of rectal ampulla descent on pPFUS at Valsalva; intra-class correlation with clinical examination was 0.75 for ampullary descent, 0.93 for rectocele depth, and 0.91 for rectocele width [48]. Further data suggest that rectovaginal septal defects can be easily identified on pPFUS and help differentiate between a rectocoele with a defective septum, a distensible septum accompanied by prolapse symptoms, a recto-enterocele or indeed an intussusception [48]. Some studies on the use of pelvic floor imaging on patients with defecatory symptoms showed a good degree of agreement between ultrasound and defecography [49], while others reported a lower degree of agreement between the two modalities for the diagnosis of rectocele, but confirmed the high concordance for intussusception [50]. Despite dynamic perineal ultrasound showing good agreement with defecography in the diagnosis of cul-de-sac hernia in patients with evacuatory difficulty, the two techniques did not agree on the contents of the hernia, suggesting a complementary role for pPFUS in optimizing the plan for surgical treatment [51].