EP1095 - Topographic MAPLe electromyography and 3D endoanal ultrasound for co-localization of anal fistula tracts with anal sphincter dysfunction: a pilot study

Purpose/Background: Anal fistulas remain a complex entity in colorectal surgery due to their variable anatomy and potential sphincter involvement. This pilot study explores the feasibility of combining MAPLe electromyography and 3D endoanal ultrasound to achieve anatomical and functional co-localization of fistula tracts with external anal sphincter dysfunction.


Aim: To explore the feasibility of using high-resolution topographic electromyography with the Multiple Array Probe Leiden (MAPLe) system to identify external anal sphincter activity patterns during both peak and sustained voluntary contractions, and to anatomically correlate sectors of reduced activity with the tract location in patients with anal fistula.

Methods/Interventions: A prospective descriptive pilot study including two patients with cryptoglandular anal fistula was conducted. Each patient underwent high-resolution topographic electromyography using the MAPLe system and 3D endoanal ultrasound (BK Specto) with volumetric reconstruction.

The primary outcome was anatomical co-localization between the fistulous tract and MAPLe quadrants showing reduced electromyographic activity. Data were reported descriptively as feasibility observations.

Results/Outcomes: In the first case (Patient 1, Fig. 1-2), three-dimensional endoanal ultrasound (BK Specto) in transverse and sagittal planes demonstrated a transsphincteric fistula with a high intersphincteric component and posterior horseshoe extension, partially involving the external anal sphincter. The corresponding topographic surface electromyography (MAPLe) recordings during five consecutive voluntary contractions revealed a localized reduction of external sphincter activitythat coincided anatomically with the posterior fistulous tract identified on ultrasound.

In the second case (Patient 2, Fig. 3-4), 3D endoanal ultrasound in transverse and sagittal planes revealed a high posterior transsphincteric fistula slightly lateralized to the right, associated with extensive fibrosis throughout the posterior anal canal and partial compromise of the external anal sphincter and upper intersphincteric plane. MAPLe electromyography showed spatial overlap between the fibrotic posterior region and sectors of decreased sphincter contractility, demonstrating consistent anatomical and functional co-localization across both imaging modalities.

Together, these pilot observations confirm the technical feasibility and spatial correspondence between 3D endoanal ultrasound and MAPLe topography, suggesting that this combined anatomical-functional approach may enhance the characterization of sphincteric involvement in complex anal fistulas.

Conclusion/Discussion: In this pilot exploration, high-resolution MAPLe electromyography could be successfully performed in both cases and demonstrated compelling spatial concordance with 3D endoanal ultrasound in mapping anal fistula tracts relative to external sphincter dysfunction. The observed co-localization suggests that sectors of reduced sphincter contractility correspond anatomically to the fistula path as imaged by ultrasound. Although limited by sample size, these results support the technical feasibility and provide a rationale for future studies integrating functional and anatomic assessment. Future larger prospective studies are warranted to validate MAPLe as a complementary tool to imaging in surgical planning and risk stratification.

Figure 1 and 2. 3D endoanal ultrasound (A) and topographic MAPLe electromyography (B) in Patient 1 with complex anal fistula
1) Three-dimensional endoanal ultrasound (BK Specto) in transverse and sagittal planes, demonstrating a transsphincteric fistula with a high intersphincteric component and posterior horseshoe extension, partially involving the external anal sphincter.

2) Topographic surface electromyography (MAPLe) maps obtained during five consecutive voluntary contractions. A clear anatomical and functional co-localization is observed between the posterior fistulous tract and the region of decreased muscle activity in Patient 1.


Figure 3 and 4. 3D endoanal ultrasound (A) and topographic MAPLe electromyography (B) in Patient 2 with complex anal fistula.
3) Three-dimensional endoanal ultrasound (BK Specto) in transverse and sagittal planes, showing a high transsphincteric posterior fistula slightly lateralized to the right, with extensive fibrosis throughout the posterior anal canal. The fistulous tract crosses the sphincter complex, involving the external anal sphincter and the upper intersphincteric plane.

4) Topographic surface electromyography (MAPLe) maps obtained during five consecutive voluntary contractions demonstrate anatomical and functional co-localization between the posterior fistulous tract and the sectors of reduced external anal sphincter activity in Patient 2.