Fibrous Dysplasia – Radiology Board Review
- Clinical: Affects children and young adults; no sex predilection; usually asymptomatic or presents with localized pain or swelling; ribs are common site of monostotic fibrous dysplasia; etiology from abnormal bone maturation
- Etiology/Pathophys: Noninherited disorder with abnormal differentiation of osteoblasts causing replacement of normal bone and marrow by immature woven bone and fibrous stroma
- Radiograph: Lesions display ground-glass matrix, well-defined borders, cortical thinning with maintained smooth outer cortex, expansile remodeling of rib, possible bubbly or cystic lucency, no periosteal reaction unless fracture present
- CT: Intramedullary expansile lesion with ground-glass opacity, cortical thinning or endosteal scalloping, well-defined margins, no soft-tissue mass, may show expansion and possible fusiform rib enlargement
- MRI: Typically low to intermediate T1 signal, intermediate to high T2 signal, heterogeneous enhancement post-gadolinium; low T2 signal may help differentiate from other lesions in ribs
- Nuc Med: Increased nonspecific radiotracer uptake on bone scan reflecting active bone remodeling
- Signs: Ground-glass sign: homogenous hazy bone matrix; Rind sign: thick sclerotic margin in some lesions, especially in long bones but less common in ribs
- Frameworks: Classification into monostotic (single bone) versus polyostotic forms; associated syndromes include McCune-Albright and Mazabraud syndromes
- DDx: Enchondroma (chondroid calcifications), aneurysmal bone cyst (fluid levels), metastasis (aggressive features, soft-tissue mass), osteofibrous dysplasia (typically tibia), rib hemangioma (vascular channels)
- Tx: Observation if asymptomatic; surgical curettage or resection for symptomatic lesions or fracture risk; bisphosphonates may reduce bone pain and turnover
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