What investigations are recommended for evaluating fibrous dysplasia?

Investigations for Fibrous Dysplasia

Plain radiographs (X-rays) are the essential first-line investigation for fibrous dysplasia, showing the characteristic ground-glass appearance with cortical thinning, and CT scan is the gold standard for confirming diagnosis and assessing extent of disease 1, 2.

Imaging Algorithm

Initial Evaluation

• Plain radiographs should be obtained first, demonstrating:
  • Ground-glass or hazy radiolucent pattern (pathognomonic feature)
  • Geographic osteolytic lesions
  • Cortical thinning and scalloping
  • Bone deformities and enlargement
  • Concave margins 1, 3

Confirmatory and Staging Studies

• CT scan is essential for:

  • Definitive diagnosis when radiographic findings are unclear 4
  • Detailed assessment of bone architecture
  • Surgical planning, particularly for craniofacial involvement
  • Distinguishing FD from other bone tumors 4
  • Evaluating complications like neural compression 1

• MRI should be added for:

  • Assessing concavity of margins
  • Detecting cystic areas within lesions
  • Evaluating soft tissue involvement (particularly in Mazabraud syndrome with myomas)
  • Ruling out malignant transformation 1
  • Assessing compressive complications 4

Extent of Disease Assessment

• Bone scintigraphy is indicated for:
  • Determining monostotic versus polyostotic distribution 2
  • Identifying all skeletal sites of involvement
  • Used selectively, not routinely 4

Tissue Diagnosis

Bone biopsy with GNAS gene mutation analysis should be performed when:

• Radiological findings are atypical or unclear 2, 5
• Differentiation from malignancy is needed 4, 5
• Monostotic forms present diagnostic uncertainty 2

Critical pitfall: Decalcification artifacts can make microscopic diagnosis challenging; multi-disciplinary review may be necessary 5.

Syndrome-Specific Investigations

For suspected McCune-Albright syndrome (polyostotic FD with endocrine abnormalities):

• Endocrine function testing for affected tissues
• Phosphate metabolism assessment (phosphate diabetes screening)
• Evaluation for precocious puberty
• Skin examination for café-au-lait macules 2, 3

Malignant Transformation Surveillance

While rare (<1% of cases), monitor for:

• Development of osteosarcoma, fibrosarcoma, or chondrosarcoma
• Aneurysmal bone cyst-like changes
• Serial imaging if clinical suspicion arises 1

The 2019 international guidelines provide the framework for systematic diagnosis and management 2, emphasizing that imaging alone suffices for typical monostotic cases, while polyostotic forms require comprehensive staging and endocrine evaluation.