What is the appropriate diagnostic and treatment approach for a adult patient with a right upper arm mass and no significant past medical history?

Diagnostic and Treatment Approach for Right Upper Arm Mass

Begin with plain radiographs of the right upper arm as the initial imaging study, followed by ultrasound for superficial masses or MRI without and with contrast for deep-seated or indeterminate lesions, then proceed to core needle biopsy for any suspicious features before definitive surgical management. 1, 2

Initial Clinical Assessment

Evaluate for specific clinical features that raise concern for malignancy:

• Mass size >5 cm in diameter 1, 3
• Deep location (beneath the deep fascia) 1, 3
• Rapid growth or recent size increase 1, 3
• Pain or tenderness (though most sarcomas present as painless masses) 1
• Fixed or immobile character 1

Critical pitfall: Physical examination alone correctly identifies only 85% of soft tissue tumors—imaging is mandatory regardless of clinical impression. 2, 3

Step 1: Plain Radiographs (First-Line Imaging)

Obtain two-view radiographs of the right upper arm to assess for: 1, 2

• Calcification (present in 27% of soft tissue masses) 1, 2
• Bone involvement or cortical erosion (present in 22% of cases) 1, 2
• Intrinsic fat content (present in 11% of cases) 1, 2
• Characteristic patterns such as phleboliths (hemangioma) or peripheral ossification (myositis ossificans) 1, 2

Radiographs demonstrate positive findings in 62% of soft tissue masses and may be diagnostic in specific entities. 1, 2

Step 2: Ultrasound or MRI Based on Mass Location

For Superficial Masses (Above Deep Fascia):

Proceed with ultrasound examination with Doppler assessment: 1, 2

• Sensitivity 94.1% and specificity 99.7% for superficial masses 1, 2
• Assess echogenicity, margins, vascularity, and relationship to neurovascular structures 1, 2
• Can differentiate solid from cystic lesions and confirm ganglion cysts 1, 2

Red flags on ultrasound requiring advanced imaging: 3

• Heterogeneous echotexture
• Increased vascularity on Doppler
• Irregular or infiltrative margins
• Size >5 cm
• Deep location

For Deep or Indeterminate Masses:

Proceed directly to MRI without and with IV contrast: 1, 3

• Superior soft tissue characterization and spatial orientation 3
• Essential for preoperative planning and local staging 1, 2
• Can differentiate benign lipomas from atypical lipomatous tumors in 69% of cases 3
• Provides assessment of neurovascular involvement and compartmental anatomy 1

Important caveat: Ultrasound accuracy drops precipitously for deep masses—MRI is mandatory in this setting. 1, 3

Step 3: Tissue Diagnosis

Core Needle Biopsy (Standard Approach):

For any mass with suspicious features, perform image-guided core needle biopsy before definitive surgery: 1, 3

• Multiple cores should be taken to maximize diagnostic yield 1, 3
• Image guidance (ultrasound or CT) is preferred over palpation-guided biopsy 3
• Plan biopsy tract so it can be excised during definitive surgery 1
• Risk of tract seeding is very small and should not prevent obtaining pre-treatment diagnosis 1

Never perform fine needle aspiration as primary diagnostic modality—it is inferior to core biopsy for sensitivity, specificity, and histological grading. 1, 3

Excisional Biopsy Exception:

Consider planned excision biopsy only for: 1

• Small subcutaneous lesions <2 cm that are indeterminate on imaging 1
• Most prove benign; if sarcoma identified, perform wide re-excision of surgical bed 1

Critical error to avoid: Inappropriate excisional biopsy of a high-grade sarcoma with positive margins dramatically increases local failure risk and may necessitate amputation if major complications occur. 4

Step 4: Staging for Confirmed Sarcoma

If biopsy confirms soft tissue sarcoma, obtain: 1

• CT chest to exclude pulmonary metastases (mandatory for intermediate and high-grade tumors) 1
• Consider CT abdomen/pelvis for high-grade sarcomas of upper extremity, especially for myxoid liposarcoma or leiomyosarcoma 1
• Regional lymph node assessment (ultrasound or cross-sectional imaging) for synovial sarcoma, clear cell sarcoma, angiosarcoma, or epithelioid sarcoma due to higher nodal involvement risk 1

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

Step 5: Definitive Management

For Benign or Low-Risk Lesions:

• Observation with clinical follow-up at 6-12 months for small, asymptomatic masses with typical benign features 3
• Surgical excision if symptomatic, rapidly growing, or causing patient anxiety 3

For Confirmed or Suspected Sarcoma:

Refer to specialist sarcoma multidisciplinary team before performing biopsy if your institution lacks definitive treatment capability. 1, 3

Treatment involves: 1, 2

• Wide excision with 1-2 cm margins for most extremity sarcomas 1
• Adjuvant radiation therapy for high-grade tumors or positive margins 1, 2
• Multidisciplinary tumor board discussion for treatment planning 1

Common Pitfalls Summary

1. Do not skip radiographs—they remain the fundamental first imaging study despite being "unrewarding" in some cases 1, 2
2. Do not rely on ultrasound for deep masses—accuracy is considerably lower than for superficial lesions 1, 3
3. Do not perform excisional biopsy without tissue diagnosis—this is the major treatment error in soft tissue tumor management 4
4. Do not delay referral to sarcoma center—soft tissue sarcomas have high mortality rates despite being rare (<1% of malignancies) 3
5. Do not assume all upper arm masses are benign—high-grade myxofibrosarcoma can present as large upper arm masses with unpredictable behavior 5