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

Next Investigation: X-ray of the Thigh

Plain radiographs in two planes should always be the first investigation for a male patient with a well-demarcated, red, painful lesion on the thigh. 1

Rationale for X-ray as Initial Investigation

The presence of pain, particularly in a well-demarcated lesion, mandates radiological assessment to exclude underlying bone pathology before any tissue sampling is performed. 2, 1 This approach is critical because:

• X-ray rapidly identifies bone involvement including destruction, periosteal reaction, soft tissue calcification, or gas formation that would fundamentally change management. 1
• X-ray is inexpensive, rapid, and provides essential information about whether deeper structures are involved, which cannot be determined by clinical examination alone. 1
• A superficial presentation does not guarantee superficial disease—a red, painful lesion could represent overlying cellulitis from underlying osteomyelitis or a bone tumor breaking through the cortex. 1

Critical Pitfall: Never Biopsy Before Imaging

Punch biopsy must not be performed before adequate imaging is obtained. 1 This is a fundamental principle because:

• Biopsy before imaging contaminates tissue planes and compromises future surgical management if malignancy is discovered. 1
• The biopsy tract is considered contaminated with tumor if malignancy is found, potentially converting a limb-salvage procedure into an amputation. 3
• Bone sarcomas are frequently difficult to recognize as malignant, and improper biopsy technique outside specialized centers leads to worse outcomes. 3

Algorithmic Approach After X-ray

If X-ray Shows Normal Findings

• Proceed to ultrasound examination with high-frequency transducer (≥10 MHz) to characterize the superficial soft tissue lesion, differentiate solid from cystic components, and identify fluid collections. 4
• Ultrasound has 94.1% sensitivity and 99.7% specificity for characterizing common superficial masses. 4
• If ultrasound findings are atypical or inconclusive, proceed to MRI for detailed soft tissue characterization. 4

If X-ray Shows Suspicious Bone Lesion

• Immediate referral to a bone sarcoma reference center before any biopsy is mandatory. 3
• Obtain MRI of the whole bone with adjacent joints for local staging at the specialized center. 2, 1
• Biopsy must be performed by the surgeon who will perform definitive resection or by a radiologist member of that specialized team. 3

Age-Specific Considerations

The patient's age influences the differential diagnosis:

• After age 40: A destructive bone lesion is more likely metastasis or myeloma than primary bone sarcoma. 1
• Between ages 5-40: Primary bone sarcoma becomes more likely. 1

Why Other Options Are Incorrect

• Punch biopsy (Option A): Contraindicated before imaging as it contaminates tissue planes and prevents proper surgical planning. 1, 3
• MRI (Option B): Only indicated after X-ray shows abnormality or when malignancy cannot be excluded with certainty on plain films. 2, 1
• Ultrasound (Option D): Appropriate for superficial soft tissue characterization but only after X-ray excludes bone involvement. 4

Answer: C. X-ray