What is the appropriate diagnosis and management for an adult patient with a subcutaneous mass and no significant past medical history?

Evaluation and Management of Subcutaneous Mass in Adults

For an adult with a subcutaneous mass and no significant past medical history, perform core needle biopsy under image guidance to establish histological diagnosis, preceded by MRI imaging if the mass is suspicious for sarcoma based on size, depth, or clinical features. 1

Initial Risk Stratification

The location and characteristics of the subcutaneous mass determine the diagnostic approach:

For Neck Masses

Identify high-risk features that warrant immediate workup rather than observation:

History red flags: 1, 2

• Mass present ≥2 weeks without significant fluctuation
• No history of infectious etiology
• Age >40 years
• Tobacco or alcohol use
• Prior head and neck cancer or radiation

Physical examination red flags: 1, 2

• Fixation to adjacent tissues
• Firm consistency
• Size >1.5 cm
• Ulceration of overlying skin
• Nontender mass

Critical pitfall: Do not prescribe empiric antibiotics unless clear signs of bacterial infection are present, as this delays diagnosis of malignancy. 1, 2

For Trunk/Extremity Subcutaneous Masses

Consider soft tissue sarcoma if the mass has concerning features:

Suspicious characteristics requiring biopsy: 1

• Deep location (subfascial or intramuscular)
• Size >2 cm
• Firm consistency
• Rapid growth
• Fixed to underlying structures

Small superficial masses (<2 cm): A planned excision biopsy may be appropriate, as these usually prove benign, with re-excision of the surgical bed if sarcoma is identified. 1

Diagnostic Workup Algorithm

Step 1: Imaging

For suspected sarcoma (trunk/extremity): 1

• MRI is the primary imaging modality
• Provides assessment of size, depth, relationship to fascia and neurovascular structures
• Helps distinguish lipoma from atypical lipomatous tumor

For high-risk neck masses: 1, 2

• CT neck with contrast (or MRI with contrast) is mandatory
• Includes targeted physical examination with visualization of larynx, base of tongue, and pharynx

Step 2: Tissue Diagnosis

Core needle biopsy is the standard approach: 1

• Multiple cores should be taken under image guidance
• Biopsy tract should be planned for removal at definitive surgery
• Risk of tract seeding is very small

For neck masses: Fine-needle aspiration (FNA) is preferred over open biopsy when diagnosis remains uncertain after imaging. 1, 2

Critical pitfall: Never perform open biopsy before completing imaging, attempting FNA, and examining the upper aerodigestive tract under anesthesia (for neck masses). 1, 2

Step 3: Staging (if sarcoma confirmed)

Most patients with confirmed soft tissue sarcoma require: 1

• CT chest to exclude pulmonary metastases
• CT abdomen/pelvis for high-grade sarcomas of lower extremities, myxoid liposarcoma, or leiomyosarcoma

Exception: Atypical lipomatous tumors of extremities without dedifferentiation have extremely low metastatic risk; chest X-ray may be adequate. 1

Special Considerations by Location

Skin/Superficial Subcutaneous Sarcomas

Dermatofibrosarcoma protuberans (DFSP): 1

• Treatment is wide surgical excision
• If inadvertently enucleated without macroscopic residual disease, wide excision with primary closure is appropriate
• Mohs surgery may be appropriate at critical anatomical sites

Atypical fibroxanthoma/pleomorphic dermal sarcoma: 1

• Usually cured by surgical excision
• Tumors with adverse features (deep subcutis invasion, necrosis, lymphovascular invasion) are regarded as pleomorphic dermal sarcomas with higher metastatic rates
• Preoperative core/punch biopsy is favored over excision biopsy

Cystic Masses

For neck masses deemed high-risk: Continue evaluation of cystic masses until diagnosis is obtained; do not assume benign. 1, 2

Management Based on Diagnosis

If Low-Risk Features Present

Observation with structured follow-up is appropriate: 1, 2

• Educate patient on warning signs requiring re-evaluation
• Document specific follow-up plan
• Advise criteria that trigger additional evaluation

If High-Risk Features Present

Proceed immediately with: 2

• Targeted physical examination
• Imaging (CT or MRI with contrast)
• Tissue diagnosis (core biopsy or FNA)
• Urgent specialist referral

Patient education requirements: 1, 2

• Explain significance of increased malignancy risk
• Explain rationale for recommended diagnostic tests
• Provide expected timeline for specialist consultation

Rare Differential Diagnoses to Consider

While establishing tissue diagnosis, be aware of uncommon presentations that may mimic benign masses: 3, 4, 5, 6

• Parasitic infections (sparganosis) in patients with history of raw frog/snake consumption
• Endometriosis in cesarean section scars (reproductive-age women with cyclic pain)
• Accessory breast tissue malignancy along milk lines
• Lymphoma presenting as subcutaneous mass without skin changes