Exploration of male urethral sphincter complex using diffusion tensor imaging (DTI)-based fiber-tracking

Area of Science:

• Radiology and Imaging Science
• Anatomy and Physiology
• Urology

Background:

• Urinary incontinence is a significant clinical issue, often linked to age-related sphincter muscle degeneration.
• The detailed anatomy of normal male sphincter muscles remains incompletely understood.
• Diffusion tensor imaging (DTI) presents a novel method to investigate muscle microstructure and fiber architecture.

Purpose of the Study:

• To characterize the anatomy of urethral sphincter muscles relevant to urinary continence using diffusion tensor magnetic resonance imaging (DT-MRI).

Main Methods:

• A prospective cohort study involving eleven healthy adult males.
• Diffusion tensor imaging (DTI) was performed using a 3T MRI scanner with a diffusion-weighted spin echo planar sequence.
• Analysis included diffusion tensor (DT) parameters (FA, eigenvalues, ADC, radial diffusivity) and fiber tracking, with statistical comparison between muscle regions.

Main Results:

• Two distinct sphincter muscles were identified: a proximal lisso-sphincter and a distal rhabdo-sphincter, surrounding a central urethral muscle fiber bundle.
• Higher fractional anisotropy (FA) and lower tertiary eigenvalue (λ₃) were observed in the proximal sphincter compared to the central urethral muscle and distal sphincter (P < 0.05).
• DTI parameter reproducibility showed an average coefficient of variation ranging from 5-12%.

Conclusions:

• Observed differences in DTI indices between urethral complex muscles suggest variations in tissue microarchitecture.
• These microarchitectural differences are likely related to the specific functional roles of the sphincter and other urethral muscles.
• DTI provides valuable insights into the microstructural anatomy of the male urethral sphincter complex, aiding in understanding continence mechanisms.