AP radiograph of the hip (upper left) shows a metaphyseal lesion that is expansile and lytic in appearance with a narrow zone of transition and no periosteal reaction. There is a transversely oriented linear density within it representing a fallen fragment sign. Coronal CT without contrast of the hip (upper right) better shows the cystic nature of the lesion and the fallen fragment. Coronal (left lower) T2 MRI without contrast of the hip shows the cystic nature of the lesion and axial T2 MRI (right lower) shows fluid / fluid levels within the lesion due to hemorrhage.
Pediatric Imaging 