What testing should be ordered to assess a lump on the forearm?

Diagnostic Approach for a Forearm Lump

For a patient with a lump on the forearm, an urgent ultrasound should be performed as the initial diagnostic test, followed by MRI if the ultrasound findings are suspicious or uncertain. 1

Initial Assessment

Risk Factors for Malignancy

• Size > 1.5 cm
• Firm consistency
• Fixation to adjacent tissues
• Ulceration of overlying skin
• Duration ≥ 2 weeks without fluctuation
• Absence of infectious etiology
• Uncertain duration of the mass

Diagnostic Algorithm

Step 1: Ultrasound Examination

• Ultrasound provides an effective initial triage tool for soft tissue masses 1
• Helps differentiate benign from malignant soft tissue masses
• Can identify common benign masses like lipomas
• Should be performed urgently (within 2 weeks) for any unexplained lump that is increasing in size 1

Step 2: Management Based on Ultrasound Findings

• If ultrasound suggests benign lipoma and no concerning features:

  • Consider local management
  • Document plan for follow-up

• If ultrasound findings are suggestive of soft tissue sarcoma OR findings are uncertain with persistent clinical concern:

  • Proceed to MRI 1

Step 3: MRI Examination

• MRI with contrast is the preferred imaging modality for soft tissue tumors affecting extremities 1
• Provides the most accurate information for diagnosis and treatment planning
• Should be performed for any mass with suspicious ultrasound findings

Step 4: Additional Testing

• Fine-needle aspiration (FNA) should be performed instead of open biopsy for masses deemed at increased risk for malignancy 1
• For cystic masses, continue evaluation until a diagnosis is obtained (do not assume benignity) 1
• Plain X-ray may be used to identify bone involvement, risk of fracture, or calcification 1

Important Considerations

When to Refer to a Specialist

• Masses with any suspicious features on imaging
• Size > 5 cm (significantly associated with malignancy) 2
• Deep location (beneath deep fascia)
• Pain (associated with malignancy) 2
• Progressive growth

Avoid Common Pitfalls

• Do not routinely prescribe antibiotics unless there are clear signs of bacterial infection 1
• Do not perform open biopsy before complete evaluation with imaging and FNA 1
• Do not assume a cystic mass is benign without definitive diagnosis 1
• Do not rely solely on clinical examination for diagnosis, as benign and malignant tumors can have considerable overlap in presentation 3

Special Considerations

• Atypical lipomatous tumors tend to be larger, deep-seated, and in the lower limb 1
• Unusual presentations may require additional specialized testing
• Consider CT chest for staging if malignancy is suspected, especially for intermediate and high-grade tumors 1

By following this systematic approach to evaluating a forearm lump, clinicians can ensure appropriate diagnosis while minimizing unnecessary procedures and avoiding delayed diagnosis of potential malignancies.