Primary aggressive chondroblastoma of the humerus: an unusual imaging presentation.

Chondroblastoma is an uncommon primary benign cartilage-producing neoplasm representing only 1% of all primary bone neoplasia, with male preponderance. It has a predilection to present in any bone ossified in the endochondral pattern. Epiphyseal location, small size, geographic margins, and cartilaginous matrix are virtually pathognomonic radiologic features of this tumor. The tumor rarely transgresses the parent bone to invade adjacent structures. We describe a histologically proven case of chondroblastoma, invading the adjacent glenohumeral joint in a 15-year-old female presented with shoulder pain, in which radiological features belied the nature of the tumor.