Bone, Non-ossifying fibroma

Non-ossifying fibromas are the most common benign tumor of bone in children with a predilection of appearing in boys rather than girls. The neoplasm is made of fibrous tissue and often occurs in the lower femur or upper tibia. Sections show fragments composed primarily of a spindle cell lesion without cytologic atypia. These are arranged in a storiform and whorling pattern. Osteoclast-like giant cells are scattered with variable density throughout. Some areas are hemorrhagic. There is focal hemosiderin deposition. There is no cytologic malignancy and no atypical mitoses are identified. Some fragments of normal or reactive adjacent bone have also been sampled.