Chondroblastoma most commonly arises in which bone region?

• A. Diaphysis
• B. Epiphysis
• C. Metaphysis
• D. Periosteum

Answer: (B)

Chondroblastoma is a benign cartilage-forming tumor that characteristically arises in the epiphysis of long bones in adolescents. This end portion near the joint—often around the knee (distal femur or proximal tibia) or nearby joints—reflects its cartilaginous origin and growth plate–related biology. On imaging it typically presents as a well-defined lytic lesion within the epiphysis, sometimes with chondroid-type calcifications, which helps distinguish it from lesions that favor other bone regions. Lesions in the diaphysis point more toward entities like Ewing sarcoma or osteomyelitis, while those in the metaphysis are classic for other processes; the periosteum is a covering, not a primary site of this tumor’s origin.