Simple bone cyst appears in x-ray as Expansile lucent lesion that is sharply demarcated from adjacent normal bone. May contain thin septa (scalloping of underlying cortex) that produce a multiloculated appearance. Tends to have an oval configuration with its long axis parallel to that of the host bone.
Simple bone cyst is a True fluid-filled cyst with a wall of fibrous tissue. Begins adjacent to the epiphyseal plate and appears to migrate down the shaft (in reality, the epiphysis has migrated away from the cyst). Bone cysts arise in children and adolescents and most commonly involve the proximal humerus and femur. Often presents as a pathologic fracture that may show the fallen fragment sign (fragments of cortical bone are free to fall to the dependent portion of the fluid-filled cyst, unlike a bone tumor that has a firm tissue consistency).