<prompt> A 45 yrs male presented with an expansile lesion in the centre of femoral metaphysis. The lesion shows endosteal scalloping punctuate calcifications. Most likely diagnosis is -OsteosarcomaChondrosarcomaSimple bone cystFibrous Dysplasia  <response>: CHONDROSARCOMA TYPES Primary chondrosarcoma Secondary chondrosarcoma Periosteal chondrosarcoma Dedifferentiated chonrosarcoma Clear cell chondrosarcoma Mesnchymal chondrosarcoma Primary chondrosarcoma Malignant cailage tumour arising in previously normal bone aka central or conventional chondrosarcoma 90 of all chondrosarcoma Age group- 40 to 60 yrs Male: female 3:2 Differenciating encondroma from chondrosrcoma Enchondroma and low grade chondrosarcoma may appear radiologically similar Similarity- both located in metaphysis with stippled calcification and endosteal scalloping Histology-- similar in enchondroma and low grade chondrosarcoma ref : maheswari 9th ed 