Multifocal fibrous Dysplasia with enchondroma-like areas: Fibrocartilaginous Dysplasia

摘要

Fibrocartilaginous dysplasia is a variant of fibrous dysplasia showing extensive cartilaginous differentiation (enchondroma-like areas). The amount of cartilage varies from case to case. This has been reported more commonly in polyostotic disease. We present a 19 year old boy who presented with multifocal osteolytic lesions involving right femoral neck and lower end of left fibula. Curettage of the lesions showed translucent cartilaginous fragments. Microscopy revealed a cartilaginous (70%) and fibro-osseous (30%) component; the former showed focally increased cellularity while the latter showed features of fibrous dysplasia. Introduction Fibrous dysplasia (FD) is an unusual developmental defect of lamellar bone formation characterized by fibro-osseous metaplasia. Monostotic form is six times more common than polyostotic FD 1. Genetic studies have shown that FD is a potentially crippling disease caused by postzygotic, activating missense mutations of GNAS1 gene, which encodes a subunit of the stimulatory G protein 2,3 .The tumor commonly occurs in 1st and 2nd decades of life. Long bones, ribs and skull are more commonly affected; however any bone can be involved. Histologically it is characterized by irregular shaped immature bony trabeculae without osteoblastic rimming arising from the surrounding spindle cell fibrous stroma. Radiologically, FD shows characteristic groundglass appearance with a rim of host bone sclerosis. Rarely, nodules of hyaline cartilage can be seen in monostotic and polyostotic cases. Some authors have used the term ‘fibrocartilaginous dysplasia' (FCD) to describe FD with extensive cartilaginous differentiation 3,4,5. FCD more commonly occurs in lower extremity, especially proximal portion of femur. Radiologically ground glass opacity with ring-like calcifications typical of cartilage, are seen 4. Sometimes the cartilaginous component is so extensive that it simulates a primary benign or malignant cartilaginous lesion. Thus differentiating FCD from other primary cartilaginous tumors is of significance in the management of these tumors. Case Report A 19 year old boy presented with the complaints of pain in the lower part of right leg of 3 months duration. Examination revealed a hyperpigmented patch over the right side of face. Local examination showed no bony tenderness. Serum alkaline phosphatase was raised (309 u/l). Other laboratory parameters were within normal limits. Radiological examination revealed lucent expansile medullary lesion having ground glass appearance in the distal end of the right fibula with ring like calcifications. Another bony expansion with subtle lucency was seen in the mid diaphyseal region of the same bone (Figure 1).