What are the treatment options for a growing arm cyst?

Treatment of Growing Arm Cyst

A growing arm cyst requires surgical excision, as increasing size indicates the lesion is not resolving spontaneously and warrants definitive treatment to prevent further growth, rule out malignancy, and provide symptomatic relief. 1, 2

Initial Diagnostic Approach

The first step is determining the cyst type through imaging:

• Ultrasound is the initial imaging modality of choice to confirm the cystic nature of the lesion and assess for any solid components that would suggest a more concerning diagnosis 3
• MRI should be obtained if ultrasound shows atypical features, including wall thickening, internal complexity, nodules, thick septa, or any solid components, as these findings raise concern for a solid mass masquerading as a cyst 4
• If contrast-enhanced MRI demonstrates any internal enhancement, a solid lesion (potentially malignant) must be suspected and managed accordingly 4

Common Arm Cyst Types and Their Natural History

Ganglion cysts are the most common cystic masses in the extremities:

• Approximately 50% resolve spontaneously without intervention 2
• However, a cyst that is increasing in size has declared itself as non-resolving and warrants active treatment 2

Epidermal inclusion cysts can occur in the arm and may grow to substantial size over years:

• These are benign but will not spontaneously resolve 1
• Large epidermal cysts (>5 cm) have been reported in the upper extremity and require surgical excision 1

Treatment Algorithm for Growing Arm Cysts

For Confirmed Simple Cysts (No Solid Components on Imaging):

Surgical excision is the definitive treatment for a growing arm cyst:

• Surgery provides lower recurrence rates compared to aspiration/injection 2
• Complete excision including the cyst wall and any pedicle connection to adjacent structures is necessary to minimize recurrence 2
• Histopathological examination after excision confirms the diagnosis and rules out unexpected pathology 1, 5

Aspiration is NOT Recommended for Growing Cysts:

• Aspiration/injection has a high recurrence rate and is suboptimal for definitive management 2
• This approach may be considered only for patients who refuse surgery or have significant surgical contraindications 2

For Cysts with Atypical Features:

If imaging reveals any of the following, biopsy or excision with wider margins may be necessary:

• Wall thickening or internal complexity 4
• Heterogeneous signal on MRI 4
• Internal nodules or thick septa 4
• Any enhancement on contrast-enhanced imaging 4

These features suggest a solid mass (potentially sarcoma) rather than a true cyst, and tissue diagnosis is mandatory before definitive treatment 4

Critical Pitfalls to Avoid

• Do not assume all cystic-appearing masses are benign cysts – solid malignancies including myxofibrosarcomas, synovial sarcomas, and undifferentiated pleomorphic sarcomas can appear cystic on imaging 4
• Do not rely on aspiration for growing cysts – the high recurrence rate makes this approach inappropriate for definitive management 2
• Do not delay imaging evaluation – MRI is essential when ultrasound shows any atypical features to avoid missing a malignant diagnosis 3, 4
• Ensure complete surgical excision including the cyst wall and any connection to adjacent joints or structures to minimize recurrence 2, 5

Preoperative Considerations

MRI provides precise anatomic localization of the cyst and its relationship to neurovascular structures, which is valuable for surgical planning 3, 5

The surgical approach should be tailored to the specific location (e.g., anterolateral approach for elbow region cysts) to ensure complete excision while protecting adjacent structures 5