Snapshot A 12-year-old boy develops mild pain in his right leg. The pain is worse at night and improves with aspirin. A radiograph of the right leg is shown demonstrating a small mass with a radiolucent nidus surrounded by reactive bone. The patient is subsequently diagnosed with an osteoid osteoma. Osteoma Definition benign bone tumor (osteogenic) derived from osteoblasts Presentation location skull mandible symptoms painless mass associated conditions Gardner syndrome Associated findings histology proliferating osteoblasts with active intramembranous ossification radiography radiodense and smooth bony mass Osteoid Osteoma Definition benign bone tumor (osteogenic) derived from osteoblasts small (< 2 cm) Presentation location proximal femur (most common) tibial diaphysis vertebrae symptoms focal pain that resolves with NSAIDs if arising in the spine, may cause painful scoliosis Associated findings histology nidus of osteoid and immature osteoblasts surrounded by a rim of reactive bone formation radiography radiolucent nidus (< 2 cm) surrounded by reactive bone Osteoblastoma Definition benign but locally aggressive bone tumor (osteogenic) derived from osteoblasts larger than an osteoid osteoma (> 2 cm) Presentation location vertebrae (most common) long bone diaphyses symptoms focal pain that is not relieved by NSAIDs if arising in the spine, may cause neurologic symptoms Associated findings histology nidus of osteoid and immature osteoblasts surrounded by a rim of reactive bone formation radiography radiolucent nidus (> 2 cm) surrounded by reactive bone large lesions may extend into soft tissues Giant Cell Tumor (Osteoclastoma) Definition benign but locally aggressive tumor derived from stromal cells with accompanying giant cells stromal cells resemble interstitial fibroblasts and are neoplastic cells giant cells are derived from monocyte/macrophage lineage and have similar characteristics to osteoclasts Presentation location metaphyseal regions of long bones distal femur (most common) proximal tibia distal radius symptoms focal pain may be referred to nearby joint Associated findings histology 3 cells types may be seen stromal cells resembling fibroblasts neoplastic cells monocyte/macrophage cells recruited from peripheral blood precursors to giant cells giant cells multiple nuclei similar to osteoclasts resorb bone radiography an eccentric lytic metaphyseal lesion that may extend into the distal epiphysis characteristic "double bubble" or "soap bubble" appearance increased activity of osteoclasts results in a cavitary lesion Osteochondroma (Exostosis) Definition benign cartilage-derived tumor (chondrogenic) containing bone and a cartilage cap arises as a lateral projection of the growth plate most common cartilage-derived tumor two forms solitary osteochondroma may be caused by Salter-Harris fracture, surgery, or radiation therapy syndromatic osteochondromas multiple hereditary exostosis (MHE) Presentation location metaphyseal regions of long bones distal femur proximal tibia proximal humerus symptoms painless mass Associated findings histology normal bony trabeculae with a thin cartilaginous cap radiography sessile (broad base) or pedunculated (narrow stalk) lesions found on the surface of bones Enchondroma Definition benign cartilage-derived (chondrogenic) tumor arises when chondroblasts and epiphyseal cartilage escape from the physis, enter the metaphysis, and proliferate second most common cartilage-derived tumor two forms solitary enchondroma syndromatic enchondromas Ollier disease Maffucci syndrome Presentation location medullary cavity in the metaphyseal or diaphyseal regions hand (most common) feet distal femur symptoms most often asymptomatic pathologic fracture Associated findings histology bland mature hyaline cartilage radiography well-defined lucent medullary lesion