What is the preferred imaging modality to detect external anal sphincter (EAS) damage after vaginal delivery?

From the Guidelines

Magnetic Resonance Imaging (MRI) with an external phased-array coil is the recommended imaging modality to detect external sphincter damage for post vaginal delivery. This recommendation is based on the most recent evidence from the Journal of the American College of Radiology, which suggests that high-resolution images achievable with external phased-array coils are preferred over endoanal MRI due to its invasive nature and potential to decrease patient acceptance and compliance 1. The use of MRI provides superior soft tissue contrast, allowing for clear differentiation between the internal and external sphincter components, identification of tears, scarring, and muscle thinning. Some of the key benefits of using MRI include:

• Superior soft tissue contrast
• Ability to identify tears, scarring, and muscle thinning
• Non-invasive procedure
• No special preparation required beyond removing metal objects While endoanal MRI may provide detailed assessment of sphincter integrity, its use is not routinely performed at most centers due to its invasive nature and potential drawbacks, such as distortion of pelvic tissues and temporary prevention of prolapse during functional assessment 1. Early detection of sphincter damage using MRI allows for timely intervention, which may include pelvic floor physical therapy or surgical repair in severe cases, potentially preventing long-term complications like chronic fecal incontinence.

From the Research

Imaging Modalities for Detecting External Sphincter Damage

• Endoanal ultrasound (EAUS) is a commonly used imaging modality for detecting external sphincter damage after vaginal delivery 2, 3, 4, 5
• Three-dimensional endoanal ultrasound (3D EAUS) can provide detailed images of the anal sphincter and surrounding structures 3, 6, 4
• External phased array magnetic resonance imaging (MRI) is also a viable option for detecting obstetric anal sphincter injuries, with moderate interrater reliability and intraclass correlation compared to 3D EAUS 4
• Transperineal three-dimensional ultrasound (3DTUS) is another imaging modality that can be used to evaluate the anal sphincter after vaginal delivery 6

Advantages and Limitations of Each Modality

• EAUS:
  • Advantages: widely available, relatively low cost, and can be performed at the bedside 2
  • Limitations: may not provide detailed images of the external sphincter, and operator dependence can affect results 2
• 3D EAUS:
  • Advantages: provides detailed images of the anal sphincter and surrounding structures, and can detect occult sphincter damage 3, 6
  • Limitations: may require specialized equipment and training, and can be time-consuming 3, 6
• External phased array MRI:
  • Advantages: can provide detailed images of the anal sphincter and surrounding structures, and can detect obstetric anal sphincter injuries 4
  • Limitations: may not be widely available, and can be more expensive than EAUS or 3D EAUS 4
• 3DTUS:
  • Advantages: can provide detailed images of the anal sphincter and surrounding structures, and can detect occult sphincter damage 6
  • Limitations: may require specialized equipment and training, and can be time-consuming 6

Clinical Applications and Future Directions

• EAUS and 3D EAUS can be used to detect external sphincter damage after vaginal delivery, and to guide surgical repair 2, 3, 6
• External phased array MRI and 3DTUS can be used to evaluate the anal sphincter after vaginal delivery, and to detect obstetric anal sphincter injuries 6, 4
• Further studies are needed to compare the effectiveness of different imaging modalities in detecting external sphincter damage, and to evaluate their clinical applications and limitations 2, 3, 6, 4, 5