X-ray is the Next Investigation
For an elderly male with a well-demarcated, red, painful lesion on the right thigh, plain X-ray in two orthogonal planes should be performed first to exclude underlying bone or deep tissue pathology before any biopsy is attempted. 1, 2
Rationale for X-ray First
Plain radiographs in two planes must always be the first investigation for any suspected bone or deep tissue lesion presenting with pain, as they rapidly identify bone destruction, periosteal reaction, soft tissue calcification, or gas formation. 1, 2
The presence of pain, especially persistent pain, mandates radiological assessment to exclude bone pathology such as osteomyelitis, bone tumor, or metastatic disease—all of which can present with overlying red, painful skin changes. 1
In elderly patients, a destructive bone lesion is more likely to represent metastasis or myeloma rather than primary bone sarcoma, making imaging even more critical in this age group. 1
Critical Pitfall: Never Biopsy Before Imaging
Punch biopsy should not be performed before adequate imaging because it can contaminate tissue planes and compromise future surgical management if malignancy is present. 3, 1, 2
Never assume a superficial presentation means superficial disease—a red, painful lesion could represent overlying cellulitis from underlying osteomyelitis or a bone tumor breaking through the cortex. 1
The biopsy tract is considered contaminated with tumor if malignancy is found, potentially requiring more extensive resection than would otherwise be necessary. 1
Algorithm After X-ray
If X-ray Shows Normal Findings:
- Proceed to ultrasound as the next step to evaluate superficial soft tissue structures, which has 94.1% sensitivity and 99.7% specificity for characterizing superficial masses. 4
- Ultrasound can differentiate solid from cystic lesions and identify fluid collections requiring drainage. 4
If X-ray Shows Suspicious Bone Lesion:
- Obtain MRI of the entire bone compartment with adjacent joints for staging before any biopsy. 1, 2
- Immediate referral to a bone sarcoma reference center is mandatory before biopsy, as the biopsy must be performed by the surgeon who will carry out definitive tumor resection. 1, 2
If X-ray and Ultrasound Are Both Normal but Symptoms Persist:
Why Not the Other Options?
Punch biopsy (Option A) is contraindicated as the first step because imaging must precede tissue sampling to avoid contaminating tissue planes and to guide appropriate biopsy site selection. 1, 4, 2
MRI (Option B) is not first-line because plain X-ray is faster, less expensive, and provides critical initial information about bone involvement; MRI is reserved for cases where X-ray findings are suspicious or inconclusive. 1, 2
Ultrasound (Option D) is appropriate only after X-ray rules out bone pathology, as it evaluates superficial soft tissue but cannot assess bone or deep structures adequately. 4