Next Investigation: X-ray First
For a well-demarcated, red, painful lesion on the thigh in a male patient, plain X-ray in two planes should be the first investigation before any biopsy is performed. 1
Why X-ray Takes Priority
Plain radiographs must always be the first investigation for any suspected bone or deep tissue lesion because they rapidly identify critical underlying pathology including bone destruction, periosteal reaction, soft tissue calcification, or gas formation. 1 This is essential because:
A superficial-appearing red, painful lesion could represent overlying cellulitis from underlying osteomyelitis or a bone tumor breaking through the cortex. 1 Never assume a superficial presentation means superficial disease. 1
The presence of persistent pain, especially night pain, warrants radiological assessment to exclude bone pathology before any tissue sampling. 1
X-rays are rapid, inexpensive, and provide critical information about whether deeper structures are involved. 1
Critical Pitfall: Never Biopsy Before Imaging
Punch biopsy should not be performed before adequate imaging, as it can contaminate tissue planes and compromise future surgical management if malignancy is present. 1 This fundamental principle prevents tissue contamination and allows proper surgical planning if malignancy is discovered. 1, 2
The biopsy tract must be considered contaminated with tumor if malignancy is found and must be removed together with the resection specimen to avoid local recurrences. 2 Improper biopsy technique performed outside specialized centers can compromise limb-salvage surgery. 3
Algorithmic Approach After X-ray
If X-ray Shows Normal Findings with Persistent Symptoms:
- Proceed to ultrasound as the next step for superficial soft tissue characterization, which has 94.1% sensitivity and 99.7% specificity for common superficial masses. 4
- Ultrasound differentiates solid from cystic lesions, identifies fluid collections requiring drainage, and characterizes the lesion's relationship to adjacent structures without radiation exposure. 4
- If ultrasound findings are atypical or inconclusive, proceed to MRI for further characterization. 4
If X-ray Shows Suspicious Bone Lesion:
- MRI of the whole bone with adjacent joints for staging is indicated when malignancy cannot be excluded with certainty on plain radiographs. 1, 2
- Immediate referral to a bone sarcoma reference center or specialized bone sarcoma network before biopsy is mandatory, as bone sarcomas are frequently difficult to recognize as malignant. 2, 3
- The biopsy must be performed at the reference center by the surgeon who will carry out definitive tumor resection or by a radiologist member of that team. 3, 2
Age-Related Differential Considerations
The most likely diagnosis relates to patient age: 2
- After 40 years of age, a destructive bone lesion tends to be metastasis or myeloma rather than primary bone sarcoma. 2, 3
- Between 5-40 years, primary bone sarcoma becomes more likely. 2
Answer: C. X-ray is the correct next investigation, as it must precede any biopsy to avoid tissue contamination and identify underlying bone pathology that could explain the superficial presentation.