A cystic, bubbly, expansile, well-defined lesion involving the right acetabulum and inferior pubic ramus is identified. It has a narrow zone of transition with benign features. There is endosteal scalloping. There is no intralesional or soft tissue calcification. There is cortical thinning however no pathological fracture or cortical break is present. The right femoral head is uninvolved. The bony pelvis is otherwise unremarkable.