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Anal sphincter atrophy is associated with a poor clinical outcome of sphincter repair in patients with faecal incontinence. Preoperative assessment of the sphincters is therefore relevant. External anal sphincter (EAS) atrophy can be detected by endoanal magnetic resonance imaging (MRI), but not by conventional endoanal ultrasonography (EUS). Three-dimensional EUS allows multiplanar imaging of the anal sphincters and thus enables more reliable anal sphincter measurements. The aim of the present study was to establish whether 3D EUS measurements can be used to detect EAS atrophy. For this purpose 3D EUS measurements were compared with endoanal MRI measurements.Patients with symptoms of faecal incontinence underwent 3D EUS and endoanal MRI. Internal anal sphincter (IAS) and EAS defects were assessed on 3D EUS and endoanal MRI. EAS atrophy was determined on endoanal MRI. The following measurements were performed: EAS length, thickness and area. Furthermore, EAS volume was determined on 3D EUS and compared with EAS thickness and area measured on endoanal MRI.Eighteen parous women (median age 56 years, range 32-80) with symptoms of faecal incontinence were included. Agreement between 3D EUS and endoanal MRI was 61% for IAS defects and 88% for EAS defects. EAS atrophy was seen in all patients on endoanal MRI. Correlation between the two methods for EAS thickness, length and area was poor. In addition, correlation was also poor for EAS volume determined on 3D EUS, and EAS thickness and area measured on endoanal MRI.Three-dimensional EUS and endoanal MRI are comparable for detecting EAS defects. However, correlation between the two methods for EAS thickness, length and area is poor. This is also the case for EAS volume determined on 3D EUS and EAS thickness and area measured on endoanal MRI. Three-dimensional EUS can be used for detecting EAS defects, but no 3D EUS measurements are suitable parameters for assessing EAS atrophy.

Conventional axial endoanal ultrasonography is somewhat limited in its utility to adequately appreciate the longitudinal extent of normal anal structures and that of perianal pathology (1). The linear extent of disease is of considerable importance in perirectal sepsis where it may adequately define the relationship of some complex fistulous tracks to the main sphincter muscle mass. In fecal incontinence, there is some evidence that less than satisfactory functional results following overlapping external anal sphincteroplasty can result from an incomplete repair of the full extent of the external anal sphincter (EAS) muscle defect itself (2,3). Here, there is a fine balance between excessive mobilization of the EAS for adequate repair and devascularization/denervation of the muscle that results in a less-thanoptimal outcome, providing some potential advantages in a preoperative imaging modality that accurately defines the rostral extent of the EAS defect. This view would be reinforced by the available results of techniques that provide high-resolution coronal images of the anal canal [most notably, endoanal magnetic resonance imaging (MRI)] and that appear to correlate anatomically with conventional endoanal ultrasonographic images and with operative findings at sphincteroplasty (4–10). Three-dimensional (3D) endoanal ultrasound represents a novel method of reconstruction from close-stepped axial endosonographic images of the anal canal using computerized software with data interpolation to create 3D images of the anal canal (11). Although not widely available and still somewhat experimental, the potential advantages of this modality will be to define constitutive gender and age differences in the normal anal canal and to validate this technique for clinical preoperative use in decision making of complex and recurrent high transand suprasphincteric fistulain-ano where there tends to be poor coupling of conventional endoanal probes against the puborectalis, and consequently a relative inability with traditional technology in adequate definition of the translevator extent of disease. In theory, 3D endoanal reconstructed images also may assist in