Characteristics of Axillary Cysts
Axillary cysts are typically benign lesions that present as solid or cystic masses on ultrasound, with specific imaging features that help distinguish them from malignant pathology. 1
Imaging Characteristics
Ultrasound Features
- Cystic lesions appear as anechoic or hypoechoic masses with well-defined borders and posterior acoustic enhancement, which helps differentiate them from solid masses 1
- Epidermal inclusion cysts demonstrate characteristic features including oval-shaped hypoechoic subcutaneous appearance with dermal attachment, intralesional echogenic reflectors, filiform anechoic areas, and absence of internal vascularity 2
- Ultrasound can reliably determine whether an axillary mass is solid or cystic, which is the primary step in management decisions 1
Size and Location
- Most benign cysts are typically less than 4 cm in size, though giant variants can occasionally occur in the axilla 2
- Cysts can arise from various structures including skin appendages (epidermal inclusion cysts), joints (ganglion cysts from the glenohumeral joint), or bursal structures 3, 4
Differential Diagnosis Considerations
Benign Cystic Lesions
- Epidermal inclusion cysts are the most common benign cystic lesions in hair-bearing areas of the axilla 2, 5
- Ganglion cysts arising from the glenohumeral joint are extremely rare but can present as axillary masses 3
- Bursal cysts occasionally occur in the axilla, though they more commonly arise from other joints 4
- Lymphangiomas represent another benign cystic entity that can develop in the axillary space 5
Important Distinctions
- Lipomas require no further evaluation once identified on ultrasound, as they are benign and have characteristic imaging features 1
- Accessory breast tissue can present as axillary masses and may contain both benign and malignant lesions 1, 5
Clinical Management Approach
Initial Evaluation
- Ultrasound of the axilla is the primary imaging modality for characterizing any palpable axillary mass, including cysts 1, 6
- Diagnostic mammography and/or digital breast tomosynthesis should complement axillary ultrasound to evaluate for underlying breast pathology, particularly when there is any suspicion of malignancy 1, 6
When to Biopsy
- Simple cysts with classic benign ultrasound features (anechoic, well-defined, posterior enhancement) typically require no biopsy 1
- Complex cystic lesions or those with solid components warrant ultrasound-guided biopsy for definitive diagnosis 1
- Any cyst with atypical features, rapid growth, or associated lymphadenopathy should undergo tissue sampling 6, 2
Critical Pitfalls to Avoid
- Do not assume all axillary masses are benign cysts without proper imaging characterization, as malignancies (including ectopic breast carcinoma) can occasionally masquerade as simple cysts 7
- Avoid relying solely on clinical examination, as physical findings alone cannot reliably distinguish benign from malignant lesions 6
- Do not delay imaging workup in patients with personal or family history of breast cancer, as the differential diagnosis broadens significantly in these populations 1