What are the potential causes and treatment options for a soft swelling in the axilla?

Soft Axillary Swelling: Diagnostic Approach and Management

For a soft swelling in the axilla, begin with axillary ultrasound as the primary imaging modality to characterize the mass and determine if it is solid, cystic, or represents lymphadenopathy, followed by diagnostic mammography in women ≥30 years to evaluate for occult breast lesions. 1

Initial Diagnostic Workup

Imaging Strategy

• Axillary ultrasound is the first-line imaging test to evaluate node morphology, assess whether masses are solid or cystic, and examine cortical thickness, uniformity, size, shape, and vascularity patterns 1, 2
• Add diagnostic mammography and/or digital breast tomosynthesis for patients ≥30 years to screen for underlying breast lesions that may present with axillary manifestations 1, 3
• For patients <30 years, ultrasound alone is sufficient unless clinical suspicion warrants additional imaging 3

When to Proceed with Tissue Diagnosis

• Perform ultrasound-guided core needle biopsy or fine-needle aspiration for any palpable axillary mass appearing suspicious on imaging, as this achieves 98-100% specificity 2, 4
• Do not rely on physical examination alone, as both sensitivity and specificity are limited for distinguishing benign from malignant causes 2

Differential Diagnosis by Clinical Context

Benign/Physiologic Causes

• Accessory breast tissue (present in 2-6% of women) can cause soft axillary swelling that mimics lymphadenopathy, particularly during hormonal changes or pregnancy 3, 4
• Reactive lymphadenopathy from infection is the most common benign etiology and may present bilaterally in autoimmune conditions 2
• Fibroadenoma in accessory breast tissue is rare but presents as a firm, well-defined, mobile mass that can be mistaken for lymphadenopathy 4

Post-Surgical/Treatment-Related Causes

• Lymphedema occurs in 3-5% after axillary clearance alone, up to 25% following axillary lymph node dissection, and below 10% after sentinel lymph node biopsy 1, 3
• The combination of axillary surgery and radiotherapy increases lymphedema risk to 40% 1, 3, 5
• Axillary web syndrome causes painful scar tissue formation and contracture extending from the axilla down the medial arm, limiting shoulder mobility 6
• COVID-19 vaccination can cause transient axillary lymph node swelling that mimics metastatic disease 7

Malignant Causes

• Breast cancer metastases are the most common malignant cause of axillary adenopathy in women with known or occult breast cancer 1
• Non-Hodgkin's lymphoma frequently presents with bilateral nodal involvement and requires tissue diagnosis 2, 8

Risk Stratification for Lymphedema

If the patient has undergone breast cancer surgery, assess these specific risk factors:

• Radiotherapy to the axilla significantly increases lymphedema risk 3, 5
• Body mass index >26 kg/m² is an independent risk factor 3, 5
• Smoking increases lymphedema risk 5
• Dissection of >18 axillary lymph nodes significantly elevates risk 5

Management Algorithm

For Suspected Lymphedema

• Immediately refer to a lymphedema specialist for patients with clinical symptoms or suggestive swelling 3
• Initiate compression bandaging, manual lymphatic drainage, and graduated compression garments 3
• Prescribe supervised progressive resistance training, which is safe and effective for reducing lymphedema 3
• Treat any infections immediately with antibiotics to prevent worsening 3
• Do not use diuretics, as they are generally ineffective for lymphedema management 3

For Suspected Accessory Breast Tissue or Benign Mass

• If imaging confirms benign features and biopsy shows fibroadenoma or normal breast tissue, reassure the patient 4
• Surgical excision is indicated only if symptomatic or if the patient desires removal 4

For Suspicious or Malignant Features

• Do not delay biopsy of suspicious nodes, as early diagnosis significantly impacts treatment planning and prognosis 2
• If breast cancer is confirmed, complete breast imaging workup with MRI identifies occult primary lesions in approximately 70% of cases 2
• Sentinel lymph node biopsy has replaced axillary lymph node dissection as standard for clinically node-negative patients 1, 2
• For patients with 1-2 positive sentinel nodes meeting ACOSOG Z0011 criteria (T1-T2, clinically node-negative, undergoing breast-conserving surgery with tangential radiotherapy and systemic therapy), sentinel lymph node biopsy alone is non-inferior to complete axillary dissection 1, 2

Critical Pitfalls to Avoid

• Never assume benign etiology without tissue diagnosis when imaging shows suspicious features, even though reactive changes are common 2
• Do not advise patients to avoid all physical activity with the affected arm; supervised progressive resistance training is safe and beneficial for lymphedema prevention 3
• Do not assume FDG uptake on PET/CT confirms malignancy, as multiple benign causes exist including infection, silicone adenitis, and post-vaccination changes 2, 7
• Consider the timing of recent COVID-19 vaccination, as axillary lymph node swelling can occur and typically resolves within one month 7
• Delaying treatment for lymphedema leads to progression and increased complication risk 3