Snapshot A 12-year-old boy presents to his pediatrician for a bony mass on his left leg. He denies any trauma to the area and it is not associated with pain. Physical examination demonstrates a palpable painless mass close to the knee joint. A radiograph of the knee demonstrates a bony outgrowth with clear, regular margins. Introduction Overview a benign chondrogenic bone tumor (osteocartilaginous exostosis) when there are 2 or more exotoses, it is termed hereditary multiple osteochondromas (HME) Epidemiology Incidence most common benign bone tumor Demographics children and adolescents more common in males Location typically affects long bones in the legs pelvis shoulder blade ETIOLOGY Pathophysiology occurs in bone that is undergoing endochondral ossiffication and results in an outgrowth of the growth plate the cartilaginous cap serves as the source of growth over the bony spur Genetics mutation EXT1 (on chromosome 8) or EXT2 (on chromosome 11) 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 Hereditary multiple exostosis symptoms often presents with limb deformities (short stature, deformed joints, and decreased range of motion) most common sites of deformity include the knee, forearm, and ankle physical exam extremity deformity decreased joint range of motion Imaging Radiograph indication initial imaging study findings 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 Differential Osteosarcoma differentiating factors painful enlarging mass or fracture Codman triangle or sunburst pattern on radiography of the bone Treatment Lifestyle observation indication asymptomatic cases Surgical excision indication in symptomatic cases Complications Tendon, soft tissue, vascular, and nerve compression Bone deformities Fracture Growth impairment Chondrosarcoma Prognosis Associated with normal life expectancy Rare transformation to chondrosarcoma