Polymorphic fibro-osseous lesions of bone: an almost site-specific diagnostic problem of the proximal femur.

Atypical fibro-osseous lesions, usually in the proximal femur, are a common consultative diagnostic problem. This is due to the fact that they contain a variety of patterns individually reminiscent of fibrous dysplasia, fibroxanthoma (non-ossifying fibroma), myxofibroma, lipoma, cyst, bone infarct, Paget's disease, and, occasionally, chondroma. The variety of patterns in a single lesion precludes a simple designation. A diagnosis based on the predominant pattern would ignore this histologic complexity, which can be predicted by location in the proximal femur and a distinctive radiographic configuration. Personal experience with 95 heterogeneous lesions indicates they are usually incidental findings. They have a broad adult age range, but quite likely have their inception in childhood and slowly alter their appearance over a lifetime. In the majority of instances asymptomatic discovery, lack of distortion of bone outline, and sclerotic borders are indications of stability over many years. Other lesions gradually enlarge, predisposing to pathologic fracture. In parallel with some enchondromas and bone infarcts, a minority of lesions undergo malignant transformation.