summary Aneurysmal Bone Cysts are benign, non-neoplastic, reactive bone lesions that most commonly occur in the femur and tibia. The condition typically presents in patients less than 20 years of age with focal pain and swelling. Diagnosis is made with radiographs showing an expansile, eccentric, and lytic lesion with bony septae and a biopsy showing blood-filled spaces without endothelial lining. Treatment is usually nonoperative for lesions associated with a fracture. Aggressive curettage, with adjuvant treatment and bone grafting, is indicated for symptomatic lesions without associated fracture. Epidemiology Demographics 75% of patients are < 20 yrs. Anatomic location 15% in spine >60% in long bones (Femur and tibia being most common) 51% occured in the lower extremities, 22.5% in upper extremities usually in metaphysis metatarsal and calcaneus are the most common locations in the foot posterior elements of pelvis may be found in similar location as telangiectatic osteosarcomas Etiology Pathophysiology primary and secondary forms login to view 5 more bullets Associated conditions associated with other tumors 30% of time login to view 5 more bullets Presentation Symptoms pain and swelling may present with pathologic fracture Physical exam neurologic deficits possible with spine lesions Imaging Radiographs expansile, eccentric and lytic lesion with bony septae ("bubbly appearance") usually in metaphyseal classic cases have thin rim of periosteal new bone surrounding lesion no matrix mineralization MRI or CT scan will show multiple fluid lines lesion can expand into soft tissue Studies Histology Characteristic findings login to view 2 more bullets cavity lining login to view 3 more bullets Differential Radiographic differential includes UBC telangiectatic osteosarcoma Histologic differential includes telangiectatic osteosarcoma giant cell tumor Differential of Aneurysmal Bone Cyst "Bubbly" lytic lesion on xray "Lakes of Blood" on histology Treatment is curettage and bone grafting Aneurysmal Bone cyst o o o UBC o NOF o Giant Cell Tumor o Chondroblastoma o Chondromyoid fibroma o Osteoblastoma o Telangiectatic osteosarcoma o Treatment Nonoperative nonoperative fracture management login to view 3 more bullets Operative aggressive curettage (+/- adjuvant) and bone grafting login to view 9 more bullets