What is the next investigation for a well-demarcated, red, painful lesion on the thigh?

Next Investigation: Plain Radiographs in Two Planes

For an elderly male with a well-demarcated, red, painful lesion on the right thigh, conventional radiographs in two planes should always be the first investigation. 1

Rationale for Radiographic Evaluation First

The European Society for Medical Oncology (ESMO) establishes that plain radiographs must be the initial imaging study for any persistent painful extremity lesion, regardless of clinical appearance. 2, 1 This approach serves multiple critical diagnostic purposes:

• Excludes underlying bone pathology including osteomyelitis, primary bone tumors, or metastatic disease that may present with overlying soft tissue changes 1
• Detects soft tissue calcification which can narrow the differential diagnosis to include myositis ossificans, calcified hematomas, or certain soft tissue tumors 1
• Rules out occult fracture even without trauma history, as elderly patients may not recall minor injuries 1
• Guides subsequent imaging decisions by determining whether MRI, CT, or tissue sampling is needed next 2, 1

Why Not the Other Options Initially

Punch Biopsy (Option A) - Contraindicated Before Imaging

Never perform biopsy before obtaining radiographs. 2, 1 ESMO guidelines explicitly state that biopsy before imaging can compromise definitive surgical management if malignancy is present, as it contaminates tissue planes and complicates limb-salvage surgery. 2, 1 The biopsy tract itself becomes contaminated and must be excised with the resection specimen if the lesion proves malignant. 2

MRI (Option B) - Premature Without Radiographs

While MRI is the best modality for local staging of soft tissue lesions, it should only be obtained after radiographs are reviewed. 2, 1 If radiographs are negative or equivocal, MRI becomes the appropriate next step to evaluate soft tissue extent and characterize the lesion. 1 Ordering MRI first wastes resources and delays diagnosis if bone pathology is present that radiographs would immediately reveal. 2

Ultrasound (Option C) - Limited Utility

Ultrasound has no established role in the initial evaluation of painful extremity lesions according to ESMO guidelines. 2 While ultrasound can guide core needle biopsy once imaging is complete, it cannot adequately assess bone involvement or provide the comprehensive evaluation needed for initial workup. 2

Critical Clinical Pitfalls to Avoid

• Do not assume this is simple cellulitis or abscess based on the red, well-demarcated appearance; deeper pathology including bone involvement or soft tissue sarcoma must be excluded radiographically first 1
• Do not delay imaging for empirical antibiotic treatment; persistent non-mechanical pain warrants immediate radiographic investigation 1
• Do not let the "well-demarcated" appearance provide false reassurance; both benign and malignant lesions can appear well-circumscribed clinically 2

Algorithmic Next Steps After Radiographs

If radiographs show bone destruction, aggressive periosteal reaction, or concerning features:

• Refer immediately to a specialized bone and soft tissue tumor center before any biopsy 2, 1, 3
• The biopsy must be performed at the reference center by the surgeon who will perform definitive resection 2, 3

If radiographs are negative or equivocal:

• Proceed to MRI without IV contrast to evaluate soft tissue extent, characterize the lesion, and assess for bone marrow involvement 2, 1
• MRI should image the entire thigh with adjacent joints for complete local staging 2

If radiographs show classic osteomyelitis changes:

• Consider bone biopsy (percutaneous or operative) for culture and histology if the diagnosis remains uncertain or if the etiologic agent needs identification 2