Aneurysmal bone cyst of the pelvis and extremities: Contemporary management Aneurysmal bone cysts are tumors of bone occurring predominantly in the metaphyses of long bones and posterior elements of spine in adolescents and young adults. Radiographically, on x-rays they appear as eccentric metaphyseal expansile lytic lesions containing “fluid-fluid” levels. Computed tomographic scan and magnetic resonance imaging clearly define the cysts and fluid-fluid levels; the former delineates cortical expansion and the latter the fibrovascular component clearly. Magnetic resonance imaging is particularly useful in differentiating aneurysmal bone cysts from malignant lesions. Histologically, these cysts are characterized by fibrovascular tissue, multinucleated giant cells, inflammatory cells, fiber-osteoid, “blue bone,” and blood filled lacunae. Chromosomal translocation has been found, implying a neoplastic basis for the development of aneurysmal bone cysts. Malignant transformation has been reported where radiation therapy was used, and in cysts associated with sarcomas. A high ratio of cellular component as compared with osteoid, and a high mitotic index have been reported to be associated with higher recurrence after treatment. Management is aimed at addressing patients’ symptoms and preventing/treating fracture, and can broadly be divided into nonoperative management (drug and radiation therapy), minimally invasive strategies (angiographic embolization, percutaneous injections), and operative management (curettage and bone grafting, en bloc excision). To reduce chances of recurrence, adjuvants such as electrocautery, high speed burr, phenol, cryotherapy, and argon beam laser have been used with variable degrees of success. With contemporary management, a cure rate of 70%–90% is expected.