<s>[INST] context: ENCHONDROMA * Rarely an enchondroma may extend through the coex and demonstrate a exophytic growth pattern. This is known as an enchondroma protuberans, and may either be seen sporadically or as pa of Oilier disease. * Almost all enchondromas are located in the medullary cavity of tubular bones. D/ds: * bone infarct , chondrosarcoma, intraosseous * other benign Ivtic bone lesions, * metastases * granulomatous disease : sarcoidosis, tuberculosis * X-ray & CT Typically enchondromas are small 1 - 2cm lytic lesions with non-aggressive features. narrow zone of transition sharply defined scalloped margins : may have mild endosteal scalloping expansion of the overlying coex may be present but there should not be coical breakthrough unless fractured Chondroid calcifications may be present : rings and arcs calcification-STIPPLED/PUNCTATE/POPCORN no periosteal reaction * The majority of enchondromas more frequ the metaphyseal region entirely arise in A cailaginous lesion in an epiphysis is more likely to be a chondrosarcoma . Refer Apleys 9th/e p 197 [/INST] question: Enchondroma commonly arises from | options: A: Ribs B: Veretebre C: Tibia D: Phalanges | answer: D </s>