Obstetric injuries of the sphincter complex can be visualized in detail with EAUS [7–11]. All childbirth trauma affects the sphincters anterior to a horizontal line through the mid-canal. Any tear of the anal sphincters posterior to this line is due to some other etiology. Tears are defined by an interruption of the fibrillar echo texture. Scarring is characterized by loss of normal architecture, with an area of amorphous texture that usually has low reflectiveness. The number, circumferential (radial angle in degrees or in hours of the clock site) and longitudinal (proximal, distal, or full length) extension of the defect, presence of scarring, differences in echogenicity and thickness of the sphincters, and other local alteration should be carefully assessed and should always be described. The operator should identify if there is an isolated or combined lesions of the IAS and EAS according to OASIS classification [40, 41]: 1° degree = vaginal epithelium lesion; 2° degree = perineal muscles damage; 3° degree = anal sphincters involvement: 3a = <50 % EAS thickness; 3b = > 50 % EAS thickness; 3c = IAS torn; 4° degree = 3° + anal epithelium torn. Defects of the IAS are easily recognized given the prominent appearance of the IAS in the mid-anal canal, and they appear as hyperechoic breaks in the normally hypoechoic ring. External sphincter tears from obstetric trauma always involve the upper sphincter, and may extend down throughout the length of the sphincter. The appearance of a defect is a break in the circumferential integrity of the mixed hyperechoic band of the EAS. A defect can have either a hypoechoic or hyperechoic density pattern. This corresponds to replacement of the normal striated muscle with granulation tissue, and fibrosis. The majority of obstetric injuries are associated with a single, large defect in the EAS anterior to the anal canal that can be linked to an additional division of the IAS (Fig. 5.7).

EAUS has an important role in detecting clinically “occult” anal sphincter injuries after a vaginal delivery. In a meta-analysis of 717 vaginal deliveries, Oberwalder et al. [42] found an incidence of occult sphincter damage of 26.9 % among a sample of 462 primiparous women and a rate of 8.5 % new defects in the group of 255 multiparas. In one-third of these (29.7 %), postpartum sphincter damage was symptomatic. As shown in this meta-analysis, the probability that postpartum FI will be associated with anal sphincter defect is 77–83 %. This analysis included five studies where EAUS was the only imaging technique used. In another study, Oberwalder et al. [14] reported that FI related to sphincter lesions is likely to occur even in an elderly population of women who experienced vaginal deliveries earlier in life. They found that 71 % of women with late onset FI (median age 61.5 years) had occult sphincter defects on EAUS. Using EAUS, Donnelly et al. [3] found anal sphincter injury in 35 % of primiparous vaginal deliveries. Sultan et al. [7] reviewed EAUS findings in 79 primiparous women before and after vaginal delivery, and identified anal sphincter defects in 28 (35 %), of whom 9 (32 %) reported altered continence to stool. Sphincter defects were not identified in those women who delivered by cesarean section. Deen et al. [13] studied 46 patients with postpartum FI and found that 87 % had a recognizable anal sphincter defect on EAUS. In a prospective study, de Parades et al. [6] did not confirm previous observations that anal sphincter injury is common after forceps delivery. In a large population of 93 healthy females, anal sphincter injury was identified by ultrasonography in < 13 % of cases after forceps delivery, and the development of FI was not related to these defects. The only factor with significant predictive value for anal sphincter injury was perineal tear. Pinta et al. [43] analyzed possible risk factors associated with sphincter rupture during vaginal delivery. A total of 52 females with a third-fourth degree perineal laceration were compared with 51 primiparous females with no clinically detectable perineal laceration. EAUS found a persistent defect of the EAS in 39 females (75 %) in the rupture group, compared with ten females (20 %) in the control group (P < 0.001). An abnormal presentation was the only risk factor for anal sphincter rupture during vaginal delivery.

High-resolution multiplanar ultrasonography may help to detect sphincter damage. Three-dimensional reconstruction offers the possibility of measuring EAS length, thickness, area and volume (Fig. 5.8) [8–11]. The relationship between the radial angle and the longitudinal extent of a sphincter tear can be assessed and graded. The length of the remaining intact sphincter muscle can also be evaluated, improving the selection of patients for surgical repair of the anal sphincter complex and helping the surgeon to judge how far the repair should extend. Using multiplanar EAUS, two scoring systems have been proposed to define the severity of the sphincter damage. Starck et al. [44] introduced a specific score, with 0 indicating no defect and 16 corresponding to a defect >180° involving the whole length and depth of the sphincters. Recently, Noderval et al. [45] reported a simplified system for analyzing defects, including fewer categories than the Starck score and not recording partial defects of the IAS. A maximal score of 7 denotes defects in both the EAS and the IAS exceeding 90° in the axial plane and involving more than half of the sphincter length. Both systems showed good intraobserver and interoberver agreement in classifying anal sphincter defects.

Ultrasonographic imaging is useful to evaluate the result of treatments. Primary repair is usually performed within 24 h of delivery; the primary end-to-end repair is carried out by the majority of obstetricians and the alternative is an overlapping repair (Fig. 5.9) [46, 47]. However, at one year follow-up, fecal urgency, FI, and perineal pain are more common in those undergoing end-to-end repair [48]. The incidence of residual anal sphincter damage on EAUS is comparable between the two techniques. In general, a sphincter defect that exceeds 3 h on the clock face or 90° (as identified by EAUS) could make overlapping technically difficult and place the repair under tension. However, a direct relationship between size of the tear and degree of dysfunction could not be confirmed [49]. Starck et al. [50] reported that the extent of endosonographic EAS defects after primary repair of obstetric sphincter tears increased over time and was related to FI. Scheer et al. [41] demonstrated the value of EAUS and manometry in counselling women who previously sustained obstetric tears. Based on specific selection criteria, the majority of women delivered vaginally without deterioration in anal sphincter morphology and function or quality of life. Savoye-Collet et al. [51] noted improvement in FI in 86 % of patients in whom EAUS documented closure of the EAS defect after anterior sphincter repair. In contrast, patients who had a persistent defect in the EAS still had significant FI. Dobben et al. [52] also found that patients with a persistent ultrasonographic EAS defect had a worse clinical outcome than those without an EAS defect. Soerensen et al. [53] assessed the long-term function and morphology of the anal sphincters and the pelvic floor after primary repair of third or fourth degrees obstetric anal sphincter injury. At a mean follow-up of 23.7 years, cases with recurrence of FI had a significantly shorter anterior EAS length compared to controls (patients repaired and still continent) when evaluated by 3D-EAUS (8.6 vs. 10.2 mm; p = 0.03). Functionally, anterior sphincter length correlated with increased severity of incontinence. Using 3D-EAUS, de la Portilla et al. [54] demonstrated that all the implants of silicone to treat FI were properly located in the intersphincteric space 3 months after injection. At 24 months, 75 % of implants were still properly located. They found that the continence deterioration suffered by most patients after the first year from the injection was not related to the localization and number of implants the patient had.

Levator avulsion is the disconnection of the muscle from its insertion on the inferior pubic ramus and the pelvic sidewall, whereas tears may occur in any part of the muscle. Avulsion is a common consequence of overstretching of the LA during the second stage of labor and occurs in 10–36 % of women at the time of their first delivery [17, 18]. It is usually occult, but it has been demonstrated in delivery suite in patients with large vaginal tears. Levator avulsion, although palpable, is more accurately detected by imaging, as the lateral attachments of the LA to the pubic bone are clearly visualized. 3D-EVUS (Fig. 5.10) [27–30] and 3D-TPUS (Fig. 5.11) [19, 20] may be utilized to document major levator trauma, as can MRI [17, 18]. The defects are usually most clearly visualized on maximal PFMC. Tomographic ultrasound imaging is particularly useful [19]. A hiatal enlargement to over 25 cm² on Valsalva maneuver is defined as “ballooning” [55].

The perineal body plays an important role in supporting the pelvic floor and the posterior vaginal wall. This structure, through the fusion with the vagina ventrally, the perineal membrane laterally, the external anal sphincter (EAS) dorsally, forms a boundary that prevents forward and downward movement of posterior compartment [36]. Damage to the PB from obstetrical trauma may be a cause of lateral displacement of the perineal membrane and because the levator ani muscle is fused with these structures this would result in widening of the urogenital hiatus seen in women with prolapse [36]. Ultrasonography has already been used to assess the integrity of the PB, however, the current 2D-US techniques are limited in resolution of fine details and only show parts of the structures involved [56–58]. As reported by Orno et al. [59], perineal muscles cannot be visualized in their entirety by using 2D-EVUS because they originate from the walls of the pelvis and converge at the PB from different angles. Three-dimensional US imaging has the potential to overcome this limit as reported by Wagenlehner et al. [36], who found that in females with third-degree rectocele, the PB appears as two separated structures angulated downward and laterally, attached like a hinge to the posterior surface of the descending pubic ramus by the deep transverse perinei muscle (Fig. 5.12).