Three-Dimensional Endoanal Ultrasound Features of the Anal Sphincter in Asian Primigravidae

Anal Sphincter Length as Determined by 3-Dimensional Endoanal Ultrasound and Anal Manometry: A Study in Healthy Nulliparous Women

OBJECTIVES

The normal female external anal sphincter (EAS) is shorter anteriorly than laterally and posteriorly. Furthermore, the thickness of the very proximal part of the circular EAS is thinner than 50% of the lateral and posterior EAS thickness. The extent of these features is not fully explored. The aim of this prospective study was to assess the normal anal sphincter with 3-dimensional (3D) endoanal ultrasound (EAUS) and to relate 3D EAUS length measurements to sphincter length determined by anal manometry.

METHODS

Healthy premenopausal nulliparous women underwent anal manometry and 3D EAUS examinations. Two experienced colorectal surgeons independently assessed all scans, blinded to any patient data.

RESULTS

A total of 43 women were included. Four scans were incomplete and excluded from the analysis. Interobserver agreement was fair to very good for the various length measurements. The mean length from the distal border of the puborectal muscle to the very proximal border of the anterior EAS (the anterior gap) was 4.4 (95% confidence interval, 3.9-4.9) mm, whereas the length to the level where the anterior EAS thickness was at least 50% of the lateral and posterior EAS thickness was 7.2 (95% confidence interval, 6.5-7.9) mm. Manometric sphincter length at rest did not correlate with any 3D EAUS length measurements.

CONCLUSIONS

In the normal anterior female anal canal, the EAS is not present or appears with less than 50% of the thickness of the lateral and posterior EAS for the first 7.2 mm below the distal border of the puborectal muscle.

Value of three-dimensional endoanal ultrasound scan (3D-EAUS) in preoperative assessment of fistula-in-ano

Objective

The aim of this study was to determine the accuracy of three-dimensional endoanal ultrasound scan (3D-EAUS) in the pre-operative assessment of fistula-in-ano in identifying the fistula tract and comparing with findings at surgery in a South Asian cohort. A retrospective analysis of 87 patients with suspected fistula-in-ano who underwent pre-operative 3D-EAUS between January 2009 and January 2016 was carried out. All patients subsequently had surgical exploration under anaesthesia (EUA), irrespective of 3D-EAUS findings. The 3D-EAUS results were compared with the surgical findings to determine the accuracy of 3D-EAUS.

Results

A total of 86 (98.9%) patients (male = 75) were subsequently shown to have a fistula at surgical exploration and of them, 3D-EAUS detected a fistula in 79 (92%) patients. In this cohort, 3D-EAUS correctly predicted the surgical findings in (n = 61, 70.9%) patients with the highest accuracy being for transphincteric fistulae (87.1%). However, the overall concordance in our study was low with a kappa coefficient of 0.318. Additional findings such as sphincter defects were detected by the 3D-EAUS in 37 patients (internal sphincter defects-21, external sphincter defects-7, both-9) which were not evident at EUA. Therefore, 3D-EAUS had a good accuracy in selected types of fistulae and particularly useful in identifying sphincter defects before surgery.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4098-2) contains supplementary material, which is available to authorized users.