Presentation
Trauma to the right ankle. The x-rays (not available) showed lytic lesions of the tarsal bones and the absence of a pathological fracture.
Patient Data
Multiple, well-defined, lobulated bony lesions involving the calcaneus, talus, lateral cuneiform, and lateral malleolus. These lesions elicit a low signal on T1, and T2 and a high signal on PD fat sat except for the talar lesion which elicits a high signal on T2 (cystic component). The postcontrast sequences show moderate heterogeneous enhancement. There is no periosteal reaction or soft tissue component.
The MRI exam was extended to the leg and showed other similar bony lesions of the fibula (proximal, middle and distal) and distal femur (lateral condyle, metaphysis).
Case Discussion
MRI features of multiple. well-defined. lobulated. bony lesions, biopsy-proven fibrous dysplasia (polyostotic form).
Fibrous dysplasia (FD) is a benign bony neoplasm (according to the WHO classification of tumors of bone, 5th edition) characterized by the failure to form mature lamellar bone and arrest as woven bone that can be multifocal.
There are two forms:
monostotic: more common, 70-80% of cases
polyostotic: less common, 20-30% of cases, often unilateral and monomelic (one limb), as in this case
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