Fibrocartilaginous dysplasia (fibrous dysplasia with extensive cartilaginous differentiation).

Fibrocartilaginous dysplasia is a variant of fibrous dysplasia in which extensive cartilaginous differentiation is identified. The amount of cartilage varies from case to case, however, no percentage has been proposed to consider this diagnosis. We present a 6-year-old girl with a two-year history of hip pain. Initial imaging studies of the right femur revealed a lucent lesion of the proximal shaft that extended into the femoral neck with ill-defined borders but well maintained cortex. Computed tomography scan demonstrated increased density of the medullary cavity but the cortex appeared intact. Curettage of the lesion was performed and fragments with cartilaginous appearance were obtained, weighing 45 g in total. Microscopically, the tumor revealed a cartilaginous (60%) and a fibro-osseous (40%) component; the former had increased cellularity and some chondrocytes displayed moderate atypia and binucleation, while the latter showed features of fibrous dysplasia. Areas of endochondral ossification and calcification were also identified. After five years of surgery this child is well and without evidence of recurrence. We discuss the differential diagnosis of this variant of fibrous dysplasia in the pediatric group.