Focal reactive periostitis ossificans in a long bone: radiologic and pathologic findings

Florid reactive periostitis ossificans (FRPO) is a benign juxta-cortical lesion of unknown etiology which most commonly occurs in the hands and feet. We report the radiographic, CT, and MR features of a pathologically confirmed FRPO in the distal femur, a location in which only a handful of cases has been reported. A 26-year-old male who presented with distal thigh pain initially underwent radiograph and CT, which illustrated a well-circumscribed, ossified lesion associated with the cortex of the femur without contiguity with the medullary canal. A subsequent MRI demonstrated heterogeneous signal intensity corresponding to the ossified portion of the lesion with a T2 hyperintense cartilaginous cap and surrounding edema. The lesion was surgically excised and pathologic diagnosis of FRPO, a mixture of osteoid, mature bone, cartilage and fibrous tissue, with associated inflammatory cells, was confirmed. Follow up four months after surgery revealed significant improvement in the patient's pain.