Chondroblastoma

Chondroblastomas of bone are rare benign bone tumours, arising at the cartilaginous growth plate, representing approximately 1-2% of all bone tumors. The most common sites are the proximal humerus and the proximal tibia, but the third most common site is the proximal femur. Histologically, the tumour consists predominantly of well-defined polygonal chondroblast-type cells similar to epiphyseal chondrocytes, with large nucleoli and benign-looking nuclei that have a tendency to be multilobulate and have a continuous dense band of substance along the inner nuclear membrane, intra-cytoplasmic inclusions of glycogen and lipids, numerous mitochondria and superficial secretion vesicles arising from a well developed rough endoplasmic reticulum. There are multi-nucleated giant cells, foci of chondroid matrix, with focal calcification that may acquire a "chicken wire" appearance. Aneurysmal bone cysts are associated with chondroblastoma in 14% of cases.