Transperineal three-dimensional ultrasound imaging for detection of anatomic defects in the anal sphincter complex muscles

Abstract

Background & aims: Three-dimensional ultrasound (3D-US) imaging is a powerful tool to visualize various components of the anal sphincter complex, that is, the internal anal sphincter (IAS), the external anal sphincter (EAS), and the puborectalis muscle (PRM). Our goal was to determine the reliability of the 3D-US imaging technique in detecting morphologic defects in the IAS, EAS, and PRM.

Methods: Transperineal 3D-US images were obtained in 3 groups of women: nulliparous (n = 13), asymptomatic parous (n = 20), and patients with fecal incontinence (FI) (n = 25). The IAS and EAS were assessed to determine the craniocaudal length of defects and were scored as follows: 0 = normal, 1 = less than 25%, 2 = 25% to 50%, 3 = 50% to 75%, and 4 = greater than 75%. The 2 PRM hemislings were scored separately as follows: 0 = normal, 1 = less than 50% abnormal, and 2 = greater than 50% length abnormal. Subjects were grouped according to the score as follows: normal (score 0), minor abnormality (scores of 1 and 2), and major abnormality (scores of 3 and 4). Three observers performed the scoring.

Results: The 3D-US allowed detailed evaluation of the IAS, EAS, and PRM. The inter-rater reliability for detecting the defects ranged between 0.80 and 0.95. Nullipara women did not show any significant defect but the defects were quite common in asymptomatic parous and FI patients. The prevalence of defects was greater in the FI patients as compared with the asymptomatic parous women.

Conclusions: 3D-US yields reliable assessment of morphologic defects in the anal sphincter complex muscles.

Figure 1

Cross-sectional (axial) 1 mm multi-slice imaging of the normal anal canal in a nulliparous subject. In this example the anal sphincter complex is shown at every 1 mm distance using I-Slice function of HD-11 (Philips). Marked in the figure are the IAS (black circle) and the EAS (white outer ring) are smooth, uniform and symmetrical.

Figure 2

Cross-sectional (axial) 1 mm multi-slice images of the anal sphincter complex with <50% damage – damage in the external anal sphincter (EAS) is marked with white arrows, no internal anal sphincter (IAS) damage is seen.

Figure 3

Cross-sectional (axial) 1mm multi-slice images of the anal sphincter complex 100% damage. Damage of the external anal sphincter (EAS) is marked with white arrow. Damage in the internal anal sphincter (IAS) shown with black arrows; the IAS has horse-shoe instead of the circular shape. The shape of the sphincter complex and the anal mucosa are oblong.

Figure 4

Examples of the puborectalis muscle (PRM) injury on 10mm ‘thick slice’ images of the PRM. The numbers on each panel demonstrates how each PRM hemi-sling is scored separately (see methods for details).

Figure 5

Dynamic images of the pelvic floor hiatus at rest and squeeze in the same parous woman. The injury of the puborectalis muscle is accentuated when during pelvic floor contraction (squeeze) maneuver the pelvic floor hiatus bulges out towards the side of injury (arrow).

Figure 6

Anterior-posterior length (mean + SEM) of the pelvic floor hiatus in the plane of the puborectalis muscle in the parous (n=19) and fecal incontinence patients (n=25) with different grades of PRM injury.