Diffusion tensor-based fiber tracking of the male urethral sphincter complex in patients undergoing radical prostatectomy: a feasibility study

Ana S C Verde,Eunice Carrasquinha,Celso Matos,Ana Gaivao,Nuno Loucao,Joao Santinha,Jorge Fonseca,Nikolaos Papanikolaou

doi:10.1186/s13244-020-00927-x

Abstract

ObjectivesTo study the diffusion tensor-based fiber tracking feasibility to access the male urethral sphincter complex of patients with prostate cancer undergoing Retzius-sparing robot-assisted laparoscopic radical prostatectomy (RS-RARP).MethodsTwenty-eight patients (median age of 64.5 years old) underwent 3 T multiparametric-MRI of the prostate, including an additional echo-planar diffusion tensor imaging (DTI) sequence, using 15 diffusion-encoding directions and a b value = 600 s/mm2. Acquisition parameters, together with patient motion and eddy currents corrections, were evaluated. The proximal and distal sphincters, and membranous urethra were reconstructed using the deterministic fiber assignment by continuous tracking (FACT) algorithm, optimizing fiber tracking parameters. Tract length and density, fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) were computed. Regional differences between structures were accessed by ANOVA, or nonparametric Kruskal–Wallis test, and post-hoc tests were employed, respectively, TukeyHSD or Dunn’s.ResultsThe structures of the male urethral sphincter complex were clearly depicted by fiber tractography using optimized acquisition and fiber tracking parameters. The use of eddy currents and subject motion corrections did not yield statistically significant differences on the reported DTI metrics. Regional differences were found between all structures studied among patients, suggesting a quantitative differentiation on the structures based on DTI metrics.ConclusionsThe current study demonstrates the technical feasibility of the proposed methodology, to study in a preoperative setting the male urethral sphincter complex of prostate cancer patients candidates for surgical treatment. These findings may play a role on a more accurate prediction of the RS-RARP post-surgical urinary continence recovery rate.

Highlights

The male urethral sphincter complex is responsible for the maintenance of continence in rest and stress conditions and is comprised of two structural components, the proximal lissosphincter and the distal rhabdosphincter [1]
A novel robotic surgical technique for radical prostatectomy, the Retzius-Sparing Robot-Assisted Laparoscopic Radical Prostatectomy (RS-RARP) was recently proposed by Galfano in order to preserve most of the structures related to urinary incontinence and to reduce postoperative incontinence [2]
RSRARP spares the retropubic space by passing through the Douglas pouch and avoids bladder mobilization and preserves the endopelvic fascia, the Santorini’s plexus and the puboprostatic ligaments; structures that are damaged in the conventional retropubic robotic radical prostatectomy

Summary

Introduction

The male urethral sphincter complex is responsible for the maintenance of continence in rest and stress conditions and is comprised of two structural components, the proximal lissosphincter and the distal rhabdosphincter [1]. RSRARP spares the retropubic space by passing through the Douglas pouch and avoids bladder mobilization and preserves the endopelvic fascia, the Santorini’s plexus and the puboprostatic ligaments; structures that are damaged in the conventional retropubic robotic radical prostatectomy. Despite the latter, post-surgical urinary incontinence is still a common and incompletely understood long-term limiting side effect that severely impacts a patients’ quality of life [3]. DTI of the prostate and adjacent structures has been focused on differentiating between benign and malignant prostate tissue [12], investigating age-related differences of the prostate [13], studying the periprostatic neurovascular fibers and its relation with post-surgical erectile dysfunction [14], and more recently, exploring the male urethral sphincter complex microstructure in eleven healthy young subjects [15]

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