summary Periosteal Osteosarcomas are rare, malignant, intermediate-grade, surface osteosarcomas that occur most commonly on the diaphysis of the femur and tibia. Patients typically present between the ages of 15 to 25 years with regional pain and swelling. Diagnosis is made with radiographs showing a lesion that has a classic "sunburst or "hair on end" periosteal reaction with biospy showing cellular atypia with areas of osteoid and chondroblastic matrix. Treatment is usually neo-adjuvant chemotherapy, limb salvage surgical resection, followed by adjuvant chemotherapy. Epidemiology Incidence extremely rare intermediate grade surface osteosarcoma Demographics usually occurs in patients 15 to 25 years of age more common in females than males Anatomic location occurs most commonly in the diaphysis of long bones femur and tibia are most common Etiology Genetics germ-line mutation of p53 found in 15-20% of cases Presentation Symptoms pain is the most common presenting symptom 25% present with pathologic fracture Physical exam regional swelling and tenderness Imaging Radiographs lesion has a classic "sunburst" or "hair on end" periosteal reaction often sunburst periosteal reaction occurs in a saucerized cortical depression typically there is no involvement of the medullary canal Chest CT scan required for staging evaluates for the presence of pulmonary metastasis Bone scan required for staging usually very hot Histology Classically grossly tumor appears lobular and cartilaginous while tumor produces osteoid, histology reveals areas of chondroblastic matrix if histology shows no osteoid production, tumor would be classified as a chondrosarcoma Treatment Operative (same as intramedullary osteosarcoma) multi-agent chemotherapy and limb salvage resection indications standard of care in most patients chemotherapy preoperative chemotherapy given for 8-12 weeks followed by maintenance chemotherapy for 6-12 months after surgical resection surgical resection trend towards limb salvage whenever possible Prognosis 20-35% chance of pulmonary metastasis Intermediate prognosis between parosteal and intramedullary osteosarcoma 90-98% necrosis with neoadjuvant chemotherapy is good prognostic sign Expression of multi-drug resistance (MDR) gene portends very poor prognosis cells can pump chemotherapy out of cell present in 25% of primary lesions and 50% of metastatic lesions