What is the best imaging modality for diagnosing a rectovaginal fistula?

From the Guidelines

The best imaging modality for diagnosing a rectovaginal fistula is MRI pelvis without and with IV contrast or CT pelvis with IV contrast, as these procedures are equivalent alternatives and usually appropriate as the initial imaging for suspected rectovaginal fistula. When considering the diagnosis of a rectovaginal fistula, it is crucial to prioritize imaging modalities that offer high sensitivity and specificity for detecting the fistula and its complications. According to the American College of Radiology Appropriateness Criteria 1, MRI pelvis without and with IV contrast or CT pelvis with IV contrast are recommended as the initial imaging modalities for suspected rectovaginal fistula.

Key Considerations

• The choice between MRI and CT pelvis should be based on the availability of expertise, patient factors, and the suspected complexity of the fistula.
• MRI provides superior soft tissue contrast, which can be beneficial in characterizing complex or recurrent fistulas, especially when combined with T2-weighted sequences and contrast enhancement.
• CT pelvis with IV contrast is an equivalent alternative to MRI and can provide detailed information about the fistula and its relationship to surrounding structures.

Additional Imaging Modalities

• Endoanal ultrasound is another imaging modality that can be used to diagnose rectovaginal fistulas, particularly for simple fistulas, with reported sensitivity and specificity of 92% and 100%, respectively 1.
• However, endoanal ultrasound may have limitations in visualizing complex or extrasphincteric fistulas, and its accuracy may be lower compared to MRI or CT pelvis.

Clinical Decision-Making

• The choice of imaging modality should be individualized based on the patient's clinical presentation, suspected location of the fistula, and available expertise.
• Direct visualization through examination under anesthesia remains the gold standard for definitive diagnosis, often combined with imaging for preoperative planning.
• The goal of imaging is to provide accurate diagnosis and characterization of the fistula, which is essential for guiding treatment and improving patient outcomes.

From the Research

Imaging Modalities for Diagnosing Rectovaginal Fistula

• MRI is often considered the imaging modality of choice for evaluation of fistulae owing to its superior soft-tissue contrast and ability to provide surgeons with the highest quality information derived from just one study, including anatomic location of fistulae and associated pelvic pathology 2.
• Endoanal ultrasound is not useful in imaging rectovaginal fistulas and cannot be recommended as a diagnostic or screening tool for the identification of a rectovaginal fistula, but it can be used preoperatively to identify and map occult sphincter defects 3.
• Vaginography is a sensitive and informative investigation for identification and delineation of vaginal fistulas, with a sensitivity of 79 percent, and is recommended as the initial investigation of choice in patients with clinically suspected vaginal fistulas 4.
• MRI with rectal administration of perflubron is a superior modality for imaging of fistulae, compared with conventional methods, since it allows a noninvasive means of demonstrating the presence of a fistula as well as offers improved qualitative assessment of fistulous disease 5.

Factors Influencing Outcome in Rectovaginal Fistula Repair

• Anal sphincter integrity and function influences outcome in rectovaginal fistula repair, and patients with clinical or anatomic sphincter defects should be treated by sphincteroplasty with levatoroplasty 6.
• Preoperative evaluation for occult sphincter defects by endoanal ultrasound or anal manometry is recommended for all patients with rectovaginal fistula 6.