What is the next step in evaluating a patient-reported mass in the left axilla (armpit)?

Diagnostic Approach to Axillary Mass in the Left Armpit

Ultrasound of the axilla should be the first-line imaging modality for evaluating a patient-reported mass in the left axilla. 1

Initial Diagnostic Algorithm

1. Axillary Ultrasound

   • Gold standard first-line imaging for axillary masses 2, 1
   • Evaluates nodal characteristics:
     • Size (suspicious if short-axis diameter >1 cm)
     • Cortical thickness (suspicious if >0.3 cm)
     • Hilar morphology (absence of fatty hilum suggests malignancy) 1
   • Can identify accessory breast tissue and other benign etiologies 2
   • Allows for image-guided biopsy if suspicious features are present

2. Additional Imaging Based on Age and Clinical Suspicion

   • For patients ≥30 years: Add diagnostic mammography or digital breast tomosynthesis (DBT) 1
   • For patients <30 years: Ultrasound alone is sufficient initially 1
   • If chest wall involvement is suspected: Consider CT chest 2

3. Tissue Sampling (if suspicious features on imaging)

   • Core needle biopsy is preferred over fine needle aspiration (FNA)
   • Higher sensitivity (88% vs 74%) with equal specificity (100%) 1
   • Should be ultrasound-guided for accuracy 1

Clinical Context and Considerations

Differential Diagnosis

• Benign etiologies (most common):

  • Reactive lymphadenopathy (infection, inflammation)
  • Accessory breast tissue
  • Lipoma 3
  • Nerve sheath tumors 2
  • Inflammatory/autoimmune conditions 2

• Malignant etiologies:

  • Metastatic breast cancer (most common malignant cause) 1
  • Lymphoma
  • Other metastatic malignancies 1

Important Caveats and Pitfalls

• Low malignancy rate: Only 7% of biopsied abnormal nodes detected on axillary US were found to be malignant in women with no personal history of breast cancer 2

• Avoid these common errors:

  • Failure to perform appropriate breast imaging in patients ≥30 years
  • Over-reliance on mammography alone
  • Missing non-breast etiologies such as systemic diseases or lymphoma 1

• Special scenarios:

  • If biopsy confirms metastatic disease of breast origin but breast imaging is negative: Proceed to breast MRI 1
  • If systemic disease is suspected: Consider appropriate laboratory testing (CBC, CRP, ESR, etc.) 1

Follow-up Recommendations

• If ultrasound shows benign features: Clinical follow-up in 3-6 months if symptoms persist 1
• If ultrasound shows suspicious features but biopsy is benign: Follow-up imaging every 6 months for 1-2 years 1
• If biopsy confirms malignancy: Management based on specific diagnosis and staging

Axillary ultrasound provides the best initial approach for evaluating axillary masses with high diagnostic accuracy, minimal invasiveness, and the ability to guide further management decisions based on imaging findings.