Snapshot A 31-year-old man presents to his primary care provider with left knee pain. He noted a bulge on his left knee 6 months ago that has gradually grown in size. A radiograph of the left knee is shown demonstrating a large lytic tumor in the fibular head. The patient is diagnosed with a giant cell tumor. 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 Treatment surgical resection for symptomatic masses 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 Treatment observation and NSAIDs Osteoblastoma 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 and epiphysiseal regions of long bones login to view 3 more bullets symptoms focal pain login to view 1 more bullet Associated findings histology 3 cells types may be seen login to view 8 more bullets radiography eccentric lytic metaphyseal lesion that may extend into the distal epiphysis characteristic "double bubble" or "soap bubble" appearance login to view 1 more bullet Treatment curettage or marginal excision with bone grafting 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 login to view 1 more bullet syndromatic osteochondromas login to view 1 more bullet Presentation location metaphyseal regions of long bones login to view 3 more bullets 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 Treatment medical bisphosphonates denosumab surgical curettage and reconstruction 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 login to view 2 more bullets Presentation location medullary cavity in the metaphyseal or diaphyseal regions login to view 3 more bullets symptoms most often asymptomatic pathologic fracture Associated findings histology bland mature hyaline cartilage radiography well-defined lucent medullary lesion Treatment observation