What is the recommended initial imaging for an axillary abscess?

Recommended Imaging for Axillary Abscess

Ultrasound of the axilla is the recommended initial imaging modality for evaluation of an axillary abscess. 1, 2

Rationale for Ultrasound as First-Line Imaging

Ultrasound offers several advantages for axillary abscess evaluation:

• Allows direct visualization of the abscess cavity
• Evaluates nodal characteristics (size, cortical thickness, hilar morphology)
• Distinguishes between fluid collections and solid masses
• Guides subsequent interventions (aspiration or drainage)
• No radiation exposure
• Cost-effective and widely available

The American College of Radiology explicitly recommends ultrasound as the modality of choice for imaging of the axilla, giving it the highest appropriateness rating (9/9) for evaluation of axillary masses 1.

Diagnostic Features on Ultrasound

When evaluating an axillary abscess with ultrasound, look for:

• Hypoechoic or anechoic fluid collection
• Internal debris or septations
• Surrounding hyperemia on Doppler imaging
• Thickened surrounding tissue indicating inflammation
• Potential foreign bodies or underlying cause

Additional Imaging Considerations

For Patients ≥30 Years:

• Consider diagnostic mammography or digital breast tomosynthesis (DBT) in conjunction with axillary ultrasound to evaluate for potential breast malignancy 2
• Mammography alone is not optimal for evaluating the axilla and has a high false-negative rate for axillary lymphadenopathy 1

For Patients <30 Years:

• Ultrasound of the breast only (no mammography) is recommended 2

For Suspected Chest Wall Involvement:

• Consider CT chest for better visualization of deeper structures 2

Ultrasound-Guided Intervention

Ultrasound guidance significantly improves outcomes for abscess drainage:

• Decreases clinical failure rates compared to drainage without ultrasound (4.4% vs 15.6%) 3
• Confirms the presence of a drainable collection
• Allows visualization of surrounding vascular structures to avoid injury
• Ensures complete drainage

Management Algorithm

1. Initial Presentation: Patient with axillary swelling, pain, erythema

   • Perform ultrasound of the axilla

2. If Ultrasound Confirms Abscess:

   • Proceed with ultrasound-guided incision and drainage
   • Note: Ultrasound-guided needle aspiration alone is insufficient therapy for skin abscesses, with only 26% success rate compared to 80% for incision and drainage 4

3. If Diagnosis Uncertain or Complex Features Present:

   • For patients ≥30 years: Add diagnostic mammography
   • If chest wall involvement suspected: Consider CT
   • If breast malignancy suspected but breast imaging negative: Perform breast MRI 2

4. After Drainage:

   • Culture the purulent material
   • Consider follow-up ultrasound to confirm resolution

Important Considerations

• The presence of MRSA decreases the success of drainage procedures (61% success with I&D vs 89% for non-MRSA infections) 4
• Recurrent axillary abscesses may indicate hidradenitis suppurativa, which often involves anaerobic bacteria 5
• Non-healing axillary abscesses despite appropriate drainage warrant further investigation, as they may rarely represent malignancy such as primary breast lymphoma 6

Pitfalls to Avoid

• Relying solely on mammography for axillary evaluation
• Failing to perform breast imaging in patients with suspicious axillary findings
• Missing non-breast etiologies such as systemic diseases, lymphoma, and other malignancies 2
• Using needle aspiration alone without incision and drainage 4

By following this evidence-based approach with ultrasound as the initial imaging modality, clinicians can optimize diagnosis and management of axillary abscesses, leading to improved patient outcomes.