There is a large expansile lytic lesion involving the left acetabulum, supra- acetabular iliac bone, extending into the ischial tuberosity and inferior ramus of the pubic bone. The cortex of the involved bone appears thin with areas of breakthrough. There is inward migration of the femoral head inside the pelvis. There is remodeling of the femoral head due to extrinsic pressure caused by the anterior column of the acetabulum.