There is a solitary, unilocular, well-defined lucent lesion centrally located within the proximal humeral metaphysis which extends into the proximal diaphysis, occupying the entire diameter of the bone. The lesion is mildly expansile with mild cortical thinning. No periosteal reaction is evident. There are multiple lucent fracture lines extending through the lesion, with two small comminuted cortical fragments within the lesion , representing the "fallen fragment sign." There is minimal offset and no angulation of the distal humerus.