What imaging is recommended for perianal abscess and fistula?

From the Guidelines

Magnetic Resonance Imaging (MRI) is the recommended imaging modality for perianal abscesses and fistulas due to its superior soft tissue resolution and ability to accurately delineate the anatomy of the anal sphincter complex.

Key Points to Consider

• Endoanal ultrasound (EUS) is an acceptable alternative when MRI is contraindicated or unavailable 1.
• For initial evaluation, a pelvic MRI with and without contrast using T1 and T2-weighted sequences should be performed, with particular attention to T2-weighted fat-suppressed sequences which highlight inflammatory changes 1.
• Gadolinium contrast enhancement helps distinguish between active inflammation and fibrosis 1.
• CT scanning is generally less useful but may be appropriate in emergency situations when MRI is unavailable or when there is concern for extensive disease 1.

Imaging Techniques

• The imaging should be performed prior to surgical intervention when possible, as it provides crucial information about the fistula tract's course, identifies secondary tracts or abscesses, and determines the relationship to the sphincter muscles 1.
• This information is essential for surgical planning and helps reduce recurrence rates by ensuring complete treatment of all diseased tissue 1.
• For follow-up assessment after treatment, MRI can evaluate healing and detect residual disease before clinical symptoms recur 1.

Clinical Considerations

• The choice of imaging modality should take into account the patient's past medical history, clinical presentation, local availability of resources, and skills 1.
• In cases of complex fistulas or suspected Crohn's disease, MRI is the preferred imaging modality due to its high sensitivity and specificity 1.

From the Research

Imaging Modalities for Perianal Abscess and Fistula

• Magnetic Resonance Imaging (MRI) is highly accurate for depicting the primary tract of fistula and abscesses in patients with perianal disease 2, 3, 4.
• MRI can be used to evaluate the activity of fistulas, which is a significant factor for determining the therapeutic strategy 2.
• Computed Tomography (CT) is an effective diagnostic imaging tool for evaluation of acute perianal abscesses and infected fistulae, especially in the emergency room setting 5.
• Endoanal ultrasound is an accurate imaging modality for delineating anatomy of perianal fistulae and abscesses, and can be used to avoid missing tracts during surgery 6.

Advantages and Disadvantages of Each Modality

• MRI:
  • Advantages: highly accurate, can evaluate fistula activity, and classify fistulas 2, 3, 4.
  • Disadvantages: may not be immediately available in the emergency room setting 5.
• CT:
  • Advantages: effective, readily available, and can guide clinical management in the emergency room setting 5.
  • Disadvantages: may not be as accurate as MRI for detecting fistulous tracts, especially complex ones 5.
• Endoanal ultrasound:
  • Advantages: accurate, low cost, and can be performed in an outpatient setting 6.
  • Disadvantages: may not be as sensitive as MRI for detecting fistula tracts or abscesses located above the puborectal muscle 6.

Recommendations

• MRI is the recommended imaging modality for evaluating perianal fistulas and abscesses, especially for complex cases or when classification is necessary 2, 3, 4.
• CT can be used in the emergency room setting when MRI is not immediately available 5.
• Endoanal ultrasound can be used as a complementary imaging modality to avoid missing tracts during surgery, especially in cases of recurrent cryptoglandular fistula 6.