Introduction A benign chondrogenic lesion derived from aberrant cartilage the most common benign bone tumor true incidence is unknown as many are asymptomatic Age & locations occur on the surface of the bone and often at sites of tendon insertion knee (proximal tibia, distal femur), proximal femur, and proximal humerus are common locations Genetics mutation in EXT gene affects prehypertrophic chondrocytes of growth plate Malignant transformation risk of malignant transformation is <1% with solitary osteochondroma ~5-10% with MHE most common location of secondary chondrosarcoma is the pelvis (usually occur as low-grade chondrosarcomas) Multiple hereditary exostosis (MHE) common disorder characterized by multiple osteochondromas autosomal dominant condition caused by mutations in EXT1, EXT2, and EXT3 genes 10% malignant transformation to chondrosarcoma in patients with MHE Presentation Osteochondroma symptoms usually present with painless mass may have mechanical symptoms or symptoms of neurovascular compression physical exam palpable mass may have mechanical symptoms secondary to mass Multiple hereditary exostosis (MHE) symptoms often presents with limb deformities (short stature, deformed joints, decrease ROM) most common sites of deformity include the knee, forearm, and ankle physical exam extremity deformity decreased joint range of motion. Imaging Radiograph sessile (broad base) or pedunculated (narrow stalk) lesions found on the surface of bones cortex of the lesion is continous with the cortex of the bone cavity of the lesion is continous with the medullary cavity of the bone Bone scan can be warm Histology Characteristic histology is similar to a normal physis with cartilage cap consists of hyaline cartilage well defined perichondrium around the cartilage cap normal primary trabeculae linear clusters of active chondrocytes may have thin cartilage cap covers lesion only 2-3 mm thick thick cartilage caps imply growth but are not a reliable indicator of malignant degeneration in children if cartilage cap becomes thicker as an adult, need to be concerned for chondrosarcoma transformation Treatment Osteochondromas nonoperative observation alone indicated in asymptomatic cases operative marginal resection including cartilage cap indicated if patient is symptomatic try to delay surgery until skeletal maturity Multiple hereditary exostosis (MHE) nonoperative most patients do not require intervention prior to reaching skeletal maturity operative surgical excision of the osteochondroma indications dislocated radial heads loss of forearm rotation outcomes simple excision of the osteochondroma optimizes chance of improved motion Differentials & Groups Surface lesions May have similar chondrogenic histology Treatment is Observation Osteochondroma / MHE • • • Periosteal chondroma • • Perosteal osteosarcoma • Periosteal osteosarcoma • Enchondroma / Olliers / Marfuccis • Chondrosarcoma • Paget's Disease • Enchondroma • NOF • Fibrous dysplasia • Eosinophillic granuloma • IBank Location Xray Xray CT B. Scan MRI MRI Histo(1) Case A prox. fibula Case B femur Case C prox. femur Case D tibia Case E fibula Case G humerus Case H distal femur (1) - histology does not always correspond to case