What is the initial imaging workup for a patient with a recurring abscess?

Initial Imaging Workup for Recurring Abscesses

For patients with recurring abscesses, MRI is the preferred initial imaging modality due to its superior soft tissue resolution and higher detection rates, particularly for complex or recurrent cases. 1

Imaging Selection Algorithm

• Clinical examination first: Most typical anorectal abscesses can be diagnosed through clinical examination alone, including digital rectal examination (DRE), without the need for imaging 2, 1
• MRI pelvis without and with IV contrast: First-line imaging choice for recurring abscesses, suspected fistulas, or when detailed anatomical information is needed 2, 1
• CT with IV contrast: Alternative when MRI is unavailable, contraindicated, or when emergency assessment is needed 2
• Endoanal ultrasound: Useful for perianal abscesses but highly operator-dependent 2

Specific Imaging Recommendations by Abscess Location

Anorectal Abscesses

• MRI pelvis: Provides superior soft tissue resolution with reported accuracy rates significantly higher than CT for detecting fistulous tracts and complex abscesses 2, 1
• CT scan: Has lower sensitivity (approximately 77%) for perirectal abscesses compared to MRI, with further reduced sensitivity in immunocompromised patients 2
• Transperineal ultrasound: Emerging as a point-of-care option for diagnosing perianal and perirectal abscesses, but results are highly operator-dependent 2

Abdominal/Pelvic Abscesses

• CT abdomen/pelvis with IV contrast: Often used in acute settings for suspected intraabdominal abscesses 2
• Ultrasound: First-line for suspected gynecological or urological sources of infection, particularly valuable in patients of childbearing age 2
• WBC scans: May be considered when initial cross-sectional imaging is inconclusive in determining the origin of recurrent sepsis 2

Special Considerations for Recurring Abscesses

• Fistula evaluation: Recurring abscesses often indicate an underlying fistula that requires identification; MRI is superior for this purpose with correct classification rates of up to 82% compared to only 24% with CT 2, 1
• Inflammatory bowel disease: Consider colonoscopy in addition to MRI when there is concern for inflammatory bowel disease, which is associated with complex and recurrent perianal abscesses 2, 1
• Post-treatment imaging: Routine imaging after incision and drainage is not required, but follow-up imaging is recommended for recurrent cases 2

Clinical Pitfalls to Avoid

• Relying solely on CT: While more readily available, CT has limited soft tissue resolution in the pelvis and may miss small abscesses or fistulous tracts 2
• Inadequate assessment of extent: Recurring abscesses often have complex anatomy with potential horseshoe extensions or multiple loculations that require detailed imaging for complete drainage 2
• Missing underlying conditions: Recurrent abscesses may indicate underlying conditions such as inflammatory bowel disease, immunodeficiency, or anatomical abnormalities that require specific imaging protocols 2, 1
• Overlooking pulmonary arteriovenous malformations: In patients with recurrent brain abscesses of unknown cause, CT pulmonary angiogram should be considered 2

Practical Approach to Recurring Abscesses

1. Complete clinical examination including thorough history focusing on previous episodes, underlying conditions, and digital rectal examination when appropriate 1
2. MRI pelvis without and with IV contrast as the primary imaging modality for recurring abscesses 2, 1
3. Additional targeted imaging based on suspected source (e.g., CT thorax-abdomen-pelvis for unclear source of infection) 2
4. Consider specialist consultation (ENT, maxillofacial) for suspected sources in those areas 2
5. Follow-up imaging at regular intervals (e.g., every 2 weeks) after treatment until clinical cure is evident 2