A, Radiolucent aneurysmal bone cyst of left proximal tibial metaphysis in 10-year-old boy. B and C, Coronal and axial MR images show multiloculated lesion with multiple fluid-fluid levels consistent with aneurysmal bone cyst. D, CT shows thin rim of remaining cortex over lesion. Biopsy confirmed diagnosis. E, Intraoperative photograph of multiloculated blood-filled cavity. F, After removal of cyst lining with large curets, tumor cavity is enlarged with power bur. G, Tumor cavity is treated with argon beam coagulation. Cavity was packed with freeze-dried cancellous bone chips and demineralized bone matrix. H, Postoperative anteroposterior radiograph. I, Radiograph 1 year later shows complete remodeling with no evidence of recurrence.